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B M MOD M71 







Abraham livinston, O.D, 










Ophthalmic Dictionary 


Pronunciation, Derivation and Definition 


Optometry and Ophthalmology 

Together with a complete descrip- 
tion of the light wave theory, 
Anatomy of the Eye, functions, 
blood and nerve supply of the dif- 
ferent parts, lietinoscope, Oph- 
thalmoscope, Trial Case and how 
to use them. Rules, Transposi- 
tion, Toric and other lenses. 
State board questions. 


rrofessor of Optometry in the Nortluru Illinois Col- 
lege of Ophthalmology and Otology, Chicago. 

Revised and Enlarged Illustrated 

Copyright, 1908, 1910, 1913, 1916, J. J. LEWIS 



To the Profession: 

This edition has been compiled with a great 
deal of care. Realizing that perfection in its 
full sense has never been attained by mortal man, 
the author invites the unbiased and conscientious 
criticism of the readers and users of this Dictionary 
and hereby earnestly solicits the same to the end 
that the future editions may profit by the honest 
convictions of studious oculists, physicians and 

I cannot conclude without expressing my deep 
sense of obligation to the profession for their kind 
reception of this work. Feeling the responsibility 
incurred by those who attempt to teach others, I 
have spared no amount of labor or cost to render 
this volume clear, practical and useful. 
Very respectfully, 





THE very favorable reception accorded (he 
fourth edition of this work has encourajjed 
the author to still further revise it, incorporating 
in its pages a considerable number of new defini- 
tions, as well as giving an accurate and complete 
derivation of all the technical terms used in 
Optical nomenclature, making the book of the 
highest value to the practitioner and student 

In presenting this fifth edition of the Lewis 
Dictionary and Encyclopedia, I wish to express 
my appreciation for the invaluable assistance 
extended by 

J. B. McFATRICH. M. S.. M. D., 

Professor of the Principles of Ophthalmology and Oto'ogv. 


Professor of Clinical and Didactic Ophthalmology and 



Professor of Anatomy and Physiology of the Eye aiil 



Professor of Dioptrics. 

J. 3. L. 


Abbreviations and Optical Signs 

Ace Accommodation. 

Aet Age. 

Am Ametropia. 

An Anisometropia. 

As Astigmatism, 

Asth Asthenopia. 

Ax Axis. 

Cc. or — ( minus ) Concave. 

Ce Centigrade. 

Cm Centimeter. 

Cx. or + (plus) Convex. 

Cyl Cylinder. 

D. Dioptry, 

D. Cc Double concave. 

D. Cx Double convex. 

D. T Distance test. 

E. or Em Emmetropia. 

e. g For example. 

H. or Hy Hypermetropia. 

In Inches. 

L. or J.. E Left eye. 

M. or My Myopia. 

Mm Millimeter. 

N Nasal. 

Nv Naked vision. 

O. D. (Oculus Dexter) .... Right eye. 
O. S. (Oculus Sinister) . . . Left eye. 

O. U. (Oculi Unati) Both eyes. 

P. or Pb Presbyopia. 

P. Cc Periscopic concavC: 

P. Cx '. Periscopic convex. 

ADDrevialions ana uptical ;!)igns — L.on. 

P. D Inter-Pupillary distance. 

PI : Piano. 

p. p. (Punctum 

Proximum) Near point. 

p. r. (Punctum 

Remotum) Far point. 

Pr Prism. 

R. or R. E Right eye. 

R. T Reading test. 

Rx Prescription. 

Sb Strabismus. 

S. or Sph Spherical. 

T Temporal. 

Ty Type. 

V Vision. 

Ya Visual acuteness. 

W. P Working point. 

-r Plus convex. 

— Minus — concave. 

C • Combined with. 

° Degree. 

A Prism Dioptry. 

= Equal to. 

x Infinity, 20 ft. or farther. 

" Line, 12th part of inch. 

± Plus or (and) minus. 

V Centrad. 

X Multiplied by; times. 

-^ Divided by. 

> Is (or are) greater than. 

< Is (or are) less than. 

Lewis Ophthalmic Dictionary 

/iL (Gr. alpha, privative.) A prefix convejing a 
negative meaning; as without, away, not, from. 

Abaxial (ab-aks'-e-al). Not situated in the line of 
the axis. 

Abbe, Prof. Ernst. A German professor and in- 
ventor of an apparatus for measuring the in- 
dices of refraction. 1845-1905. 

Abducens (ab-du'-senz). (L. ab. = from + ducere 
= to draw.) The external rectus muscle, whose 
action it is to rotate the eye outward. It arises 
by two heads, one from the lower margin of the 
sphenoidal fissure; the other from the outer 
margin of the optic foramen. Its tendon is in- 
serted into the sclera 8 mm. from the outer 
margin of the cornea. Under normal conditions 
these muscles should overcome about 8 degrees 
of prism, base in. It is controlled by the sixth 
pair of cranial nerves (abducens). 

Abducent (ab-du'-sent). Abducting; drawing from 
the center. 

Abduct (ab = away, ducere = to lead). To draw 
away from the median line. 

Abduction (ab-duc'-shun). The act of turning the 
eye outward from its position of rest. For test- 
ing the power of the abductors or external recti 
muscles, use the strongest prism, base in, with 
which the eyes can overcome diplopia, looking 
20 feet away, and deduct any imbalance. 


Abductor (ab-duc'-tor). Any muscle that abducts. 
For instance, abductor oculi. the external rectus 

Aberration (ab-er-a'-shun). (L. ab = away, errare 
= to wander.) Wandering from normal. When 
applied to lenses would mean, unable to obtain 
a perfect focus. It is due to the greater refrac- 
tive power of the edge over the center of convex 
lenses, thus causing the image to be somewhat 
blurred. In the eye the iris shuts off the edge of 
the lens, and in this way prevents spherical 
aberration. Chromatic Aberration, dispersion of 
colors. Owing to the colored rays having differ- 
ent degrees of refractibility they are not focused 
at the same distance. 

Ablatio-retinae (ab-la'-she-o-ret'-in-e). (L. ab = 
away -f latum = to take.) Detachment of the 

Ablepharia (ah-blef-ar'-e-ah). (Gr. a = not + 
blepharon = eyelid.) That condition in which 
the eyelids are absent. Also, Ablepharous. 

Ablepsia (ah-blep'-se-ah). (Gr. a = not + blepo ^ 
I see.) Blindness — want of sight. 

Abnormal (L. ab = away + normal = ?ule). Away 
from normal. Relating to vision would mean, 
any defect of sight. (Ametropia.) An eye 
wherein parallel rays of light do not focus on 
the retina with the muscles of accommodation 
at rest. 

Abrasio-cornea (ab-ra'-si-o-cor'-ne-ah). (L. ab - 
away + radere = to scrape.) The rubbing off of 
the outer layer of the cornea. 

Abscess (ab'-ses). (L. ab — away + cedere = to 


depart.) A collection of pus in any cavity 
formed by the separation of tissue. 

Abscissa (ab-sis'-a). (L. cut off.) A certain line 
used in determining the position of a point in a 

Absorption (ab-sorp'-shun). (L. ab, and sorbere = 
to suck in.) A term applied in the operation for 
cataract where the lens capsule is needled, 
allowing the aqueous humor to absorb the lens. 

Absorptive. Anything that has the power of ab- 

Abstract (ab'-strakt). (L. abstractus = drawn 
away.) An abstract number is a number not 
designated as referring to any particular class 
of objects. 

Acceleration. An increase in rapidity; opposed to 

Accommodation (ak-kom'-mo-da'-shun). (L. ac- 
commodare = to depart.) The act of adjusting 
the eye to see within its far point of vision. 
Optical adjustment. It takes place by contract- 
ing the ciliary muscles which encircle the crys- 
talline lens and draws forward the inner layer 
of the choroid and hyaloid membrane, the sus- 
.pensory ligaments becoming relaxed, and the 
lens (by its own elasticity) allowed to assume 
a greater convexity, especially its anterior sur- 
face, thus increasing its refraction. It is never 
used unless the light attempts to focus behind 
the retina. Amplitude of Accommodation is the 
difference in the dioptric power of the eye when 
in a state of complete relaxation and when the 
full amount of accommodation is in use; or. in 
other words, the amount of accommodation an 


eye possesses. Amplitude of Accommodation at 
different ages (from Landolt) as follows: 

Age in Amplitude 

Years (dioptrics) 

10 14 

15 12 

20 10 

25 8.5 

30 7.0 

35 5.5 

40 4.5 

45 3.5 

50 2.0 

55 1.75 

60 1.0 

65 0.75 

70 0.0 

This is approximately correct, but individuals 
differ in the amount of accommodation they 
possess at the same age. Accommodation is 
spoken of as binocular, absolute, and relative. 

Binocular Accommodation is the full amount 
of accommodation which both eyes can use 
together while converging. 

Absolute Accommodation is the total amount 
of accommodation of one eye only, the other 
being covered. 

Relative Accommodation is the amount of 
accommodation that can be used without chang- 
ing the convergence; that is, by lenses or other 

Spasm of Accommodation, the inability on 
the part of the patient to relax his accommoda- 
tion without drugs. 


Center of Accommodation is situated beneath 
the floor of the aqueduct of Silvius. 

Paralysis of Accommodation is the loss of 
power of movement in the ciliary muscles 
through injury, disease, or a drug affecting the 
nerve supply. 

Negative Accommodation would mean that 
the eye possesses the ability to decrease its 
dioptric power from that which it possesses in 
a state of rest. By so doing would lengthen its 
principal focus. 

Accommodation is interfered with by harden- 
ing of the lens, weakness of the ciliary muscles, 
paralysis of the third nerve, loss of the crystal- 
line lens, or use of drugs, such as Atropine. 

Achloropsia (Gr. a = without -{- chloros = green 
-f- opsis = vision). Green-blindness, color blind- 
ness as regards green. 

Achroma (ak-ro'-mah). (Gr. a = not + chroma = 
color.) Without color. 

Achromatic Lens (ah-kro-mat'-ik). (See Lens.) 

Achromatism (ah-kro'-ma-tism). Absence of chro- 
matic aberration. 

Achromatistous (ah-kro-mat-is'-tus). Deficient in 
coloring matter or pigment. 

Achromatopsia (ah-kro-mat-op'-se-ah). (Gr. a = 
kicking, chroma = color, eye.) Total color- 

Achromatosis (ah-kro-mat-o'-sis). Any disease 
marked by lack of pigmentation. 

Acorea (ah-ko'-re-ah). (Gr. a - not -}- kore - pu- 
pil.) When the pupil is absent. 

12 1J:\\ IS I« 'CKKT 

Acquired. Not born with, but dfV<*Ioped aft«T 

Acuity (ak u'-it-o). ( L. acuere to sharpt'ii.i 
Sharpn»'ss. like a iieodlo. The sharpiK'Hs of 
vision; thi' keenness of the visual powers. The 
acuteness of vision niran.s the vision the patient 
has with his full correction. The faculty of the 
retina to perceive forms depends on many con 

1. rriniarily, on the sensibility of the retina. 

2. On the adaptation of the retina. 

3. On the general illumination. 

4. On the sharpness of the retinal inumf. 

5. On the intensity of the illumination. 

It is known that the acuteness of vision varies 
with the general illumination up to a certain 
degree of intensity, as that of a clear, sunny 
day; the two then vary in a direct proportion, 
but when the illumination passes a certain limit 
of intensity, the acuteness of vision diminishes 
instead of Increases. 

Adaptation (ad apta'shun ). iL adaptare to 
adapt.) Adjustment of th«« pupil lo light. 

Addition ladish'-on). ( L. addrre to increase. > 
The uniting of two or more nimibnrs in one 

Adducens ( ad du'-sens ). (L. ad - towards, du 
cere to lead.) When this term is applied to 
the eye it means the ijiternal rectus muscle, tho 
muscle which turns the eyeball inward toward 
the nose, supplied by the third cranial or motor 
ocull nerve. The power of adduction of the eye 
ranges from I'O up to ."io degrees. For testing 
the power of th«' adducens or internal rectus 


muscle, use the strongest prism, base out, with 
which the eyes can overcome diplopia. 

Adduct (L. adducere = to bring toward). To draw 
inward toward a center. 

Adduction. Movement of the eyeball inward from 
its position of rest. The adducens means the 
internal rectus muscle by which we turn the 
eyes inward. The test for the power of the 
adducens is made by first correcting any error 
of refraction and have the patient look at a 
light 20 feet away, placing the base out of the 
strongest prism, with which the eyes can over- 
come diplopia. We figure from their position of 
rest and this prism registers the adduction. 

Adenectomy (ad-en-ek'-to"-me). (Gr. aden = giant! 
+ ektome = excision.) Removal of a gland by 

Adenemphraxis (Gr. aden = gland + emphraxis = 
stoppage). That condition in which the duct or 
gland is obstructed. 

Adenoid (ad'-en-oid). (Gr. aden = gland + edois 
= appearance.) Resembling a gland. 

Adenclogaditis (ad'-en-o-log-ad-i-tis'). Inflammation 
of the glands of the eyes and conjunctiva. Oph- 
thalmia neonatorum. 

Adenophthalmia (ad-en-off-thal'-me-ah). (Gr. ad^n 
^^ gland 4- ophthalmos = eye.) Inflammation of 
the meibomian glands. 

Aditus (ad'-i-tis). (L. "a passage.") The entrance 
to a canal or duct. Aditus Orbitae, the opening 
of the orbit, covered by the eyelids. 

Advancement. The cutting away of a muscle of 
the eye and attaching it to an advanced point. 

This operation is performed on the weak muscle 
in cases of strabismus. 

Adventitious (ad-ven-tish'-us). Acquired — not nor- 

Afferent (L. ad = to vf ferre =^ to bear). Convey- 
ing from the surface to the center, as a nerve 
or vein. 

Albinism (al'-bin-ism). (L. albus == white.) Ab- 
normal deficiency of pigment in the iris and 

Albugo (al-bu'-go). White opacity of the cornea 

of the eye. Leukoma. 
Alexia (a-lex'-ia). (Gr. a = lacking, lexia = word.) 

Unable to read, due to a central lesion. 

Amaurosis Tam-aw-ro'-sis). (Gr. amaurotin = to 
render obscure.) A disease of the optic nerve 
or retina, which causes blindness. 

Ambiopia Cam-be-o'-pe-ah). (Gr. ambo = both, 
opia ^ eye.) Vision with both eyes. 

Amblyopia (am-ble-o'-pe-ah). (Gr. amblys = blunt 
+ opsis = sight.) A dimness of vision from de- 
fective sensibility of the retina. A condition in 
which there is a possibility of restoring the 
former vision; for instance, when a person has 
an error of refraction in one eye, the other eye 
being emmetropic, he will learn to ignore the 
eye with the error, and use the one with the 
best vision. In this way the sight will become 
dim from want of use, and is an acquired state, 
which by testing with ihe pinhole disc will show 
no improvement. Under these conditions, the 
error must be corrected with the retinoscope. 
and if the eyes are not more than two dioptrics 


apart, instruct your patient always to wear his 
correction and cover the good eye two or three 
times a day, for a period of ten minutes at a 
time, and try to use the amblyopic eye. In this 
w^ay you will notice an improvement of vision 
each week. When the pinhole disc fails to im- 
prove vision, the eye is either amblyopic or in 
a diseased state. Toxic Amblyopia is a dimness 
of vision from the poisonous effect of drugs, 
such as quinine, upon the nervous system; ex- 
cessive use of tobacco or alcoholic stimulants 
produce the same effect. The treatment for this 
form of Amblyopia does not consist of glasses,- 
but the patient must quit the use of the drug 
causing the trouble, and if not too far advanced 
there is a possibility of recovering the former 
vision. A., Postmar'ital, that due to sexual ex- 
cess. A., Crossed, on one-half of retina. 

Amblyopia ex Anopsia. Amblyopia resulting from 
one eye having been excluded for some time 
from binocular vision. 

Ametrometer (a-met-rom'-e-ter). (Gr. a = lacking 
+ metron = measure.) An instrument used for 
measuring ametropia. 

Ametropia (a-met-ro'-pe-ah). (Gr. a = lacking, 
metron := measure, ops = eye.) Any error of 
refraction, such as hyperopia, myopia, or astig- 
matism. Axial Ametropia. Ametropia that is 
caused by the length of the eyeball on the optic 
axis. The opposite of Emmetropia. 

Amphice'lous (Gr. amphi = on both sides -|- koi- 
los = hollow). Concave on both sides or ends. 

Amphodiplopia (am-fo-dip-lo'-pe-ah). (Gr. ampho 

= both + diploos = double.) That condition 
where both eyes have double vision. 

Amplifier (am'-ple-fi-er). An apparatus for in- 
creasing the magnifying power of a microscope. 

Amplitude (am'-pli-tud). State of being ample. 
(Physics) The extent of a movement measured 
from the starting point or position of rest. 
(Math.) An angle upon which the value of some 
function depends. 

Amplitude of Convergence. (See Convergence.) 

Amyosta'sia (Gr. a = not + mys = muscle + sta- 
sis = standing). Nervous tremor of the muscles. 

Amyosthe'nia (Gr. a = not -f- mys = muscle -f sthe- 
nos = strength). Failure of muscular strength. 

Anacamptom'eter. An instrument for measuring 
the reflexes. 

Anaclasis (an-ak'-las-is). (Gr. bending back, re- 
flection.) When this term is applied to light, it 
refers to the rays traveling obliquely from a 
rarer to a denser medium, being bent backward 
toward the perpendicular (refraction). 

Anaesthesia (an-es-the'-ze-ah). (Gr, an = not -|- 
aisthesis = sensation. ) Lacking sensitiveness, 
where the retina is amblyopic. 

Anaesthetic (an-es-thet'-ik). The name given to 
that which produces insensibility to pain, as 
chloroform, cocaine, and ether. 

Analysis fa-nal'-i-sis). (Gr. "a releasing.") A reso- 
lution of a whole into its parts; a form of 
reasoning from a whole to its parts. 

Anaphoria (an-a-phor'-ia). (Gr. ana = up + phoria 
= tending.) That condition in which the eyes 
turn upward when the e?^trinsic muscles are in 


a state of rest. Stevens gives 33 degrees for 
the maximum elevation. 

Anastomosis (a-nas-to-mo'-sis). (Gr. anastomoo = 
"througti a mouth.") The junction of vessels; 
the joining of blood-vessels with one another 
by means of branches, whereby, if the fluid be 
arrested in its course through one vessel, it 
will proceed through others. The term is some- 
times applied to the junction of nerve filaments 
with each other. 

Anerythrop'sia. Red-blindness. 

Antecedent (an-te-se'-dent). (L. antecedere = to 
go before.) The first of two terms of a ratio. 

Anatomy (a-nat'-o-me). (Gr. anatome = dissec- 
tion; ana =: up, tome = a cutting.) (Eye.) Re- 
lates to the description of the structures of the 
eye and its parts. The eyeball is nearly sphe- 
rical in shape and measures about 24 mm. in 
diameter. The cornea represents a segment of 
a small sphere projecting from its anterior sur- 
face. The first tunic of the eyeball is the scle- 
rotic and cornea. The posterior five-sixths is 
the sclerotic, which is white and opaque, and 
serves tcT give shape to the eye and protects its 
more delicate interior. Near the posterior pole, 
on the nasal side, is a sieve-like disc known as 
the lamina cribrosa, through which the optic 
nerve fibers enter the eye. The sclerotic is 
thickest at its posterior portion and gradually 
becomes thinner as it approaches the equator, 
and again thickens as it approaches the cornea. 
The anterior one-sixth is the cornea. It is trans- 
parent and of a greater curvature than the scle- 
rotic. The cornea is set in the sclerotic as a 



Nvatch crystal is placed in its frame, and is com- 
posed of five layers, from without inward as 
follows: Conjunctiva Epithelium, Bowman's 
Membrane. Cornea Proper, Membrane of Desce- 
met. and the Endothelium. At the inner angle 
(angle of filtration) between the iris and cor- 
nea, there are a number of comb-like openings 
which are in the trabecular tissue or pectinate 

ligament which runs from the periphery ot thr 
cornea to the base of the iris. These openings 
are called the spaces of Fontana. through which 
the aqueous humor passes into the canal of 
Schlemm, a circular canal extending around the 
periphery of the cornea at the sclero corneal 

on I'm A!. Mir du^pionaijv 


junction. From this canal the humor passes into 
the anterior ciliary veins. The socoiui (uiiic of 
the oyo is comi)()so(l o[' (he choroid. ciliar>' btxly. 
and the iris. It lines tlie iiuuM- side of the scle 
rotic. and is ixM'forated to aHow llu' optic nerve 
to entiT, and has a circular opening in front, 


I'ul .sluiwiufv .Sci'Oiul Tunic. 

which is known as (he pupil. Through (his (unie 
the eye obtains i(s principal blood and nerve 
supply. This is the tunic in which (he pignuMU 
is deposited for the purpose of absorbing ligh(. 
The choroid is said to nourish (he reiina and 
the vitreous. The ciliary muscles are within (he 
ciliary body, and are used for acc()mnu)(la(ing. 
The iris is the most anterior por(ion of (he 
second tunic. It is located in front of the crys- 
talline lens, and separales the an(erior and pos 
terior chambers; it gives tlie t\ve i(s coloi-, 
regulates the amount of light which enters, and 
prevents sphori(!a.l ab(Mration of the lens. The 
(liird (unic is (lie r(>(ina. 1( is a very delicate, 
transparent membrane, made up of t(^n layers, 
one of which is (he layer of optic nerve libers. 
These libers pass tlirough (h<' lamina cribrosa 
at the op(ic disc, and lla((en ou( more and more 




,4.'^" S^-^.^';.™L-"--- BOX>; 


1 , A n fr 1 o 


as they approach the front of the eye. The 
retina is attached in two places, at the optic 
disc and at its anterior border, the ora serrata. 
It is not attached to the choroid, but simply lies 
on it. In examining the retina with the ophthal- 
moscope you will notice the optic disc on the 
nasal side, which marl^s the entrance of the 
optic nerve into the globe. The macula lutea, 
w^hich is the most sensitive spot of the retina 
(sometimes called the yellow spot, as it is said 
to turn yellow after death), is situated slightly 
on the temple side. The function of the retina 
is to receive the impressions of the waves of 
light and transmit them through the optic nerve 
to the brain. The space between the iris and 
cornea is known as the anterior chamber of the 
eye, and that between the iris and the lens, as 
the posterior chamber. Both of these chambers 
are filled with a transparent, watery fluid known 
as the aqueous humor. The large chamber back 
of the crystalline lens is known as the vitreous 
chamber, and contains the vitreous humor, 
which occupies a little more than three-fourths 
of the eyeball. It is a perfectly transparent sub- 
stance, about the consistency of the white of an 
egg, and is enclosed in a thin transparent sac 
known as the hyaloid membrane. This mem- 
brane divides at the ciliary body and forms 
what is known as the anterior and posterior 
suspensory ligaments, which are attached to the 
lens capsule, thus forming what is known as 
Petit's Canal and the Zonule of Zinn. Within 
the lens capsule the crystalline ' lens is to 
be found. In shape the lens resembles a bi- 
convexed lens, except that it is less curved in 


front than behind; in youth it is highly elastic, 
moderately firm, yet a perfectly transparent 
body, as clear as a crystal, and as we grow 
older it becomes harder and sometimes of a 
slightly straw tint. The crystalline lens is made 
up of layers closely resembling those of an 
onion, which accounts for its elasticity. The 
eyeball is imbedded in the fatty substance of 
the orbit, and is surrounded by a thin mem- 
branous sac, which isolates it and at the same 
time allows free movement. This sac is named 
the Capsule of Tenon. It is a very delicate 
membrane, consisting of two layers which in- 
vest the posterior part of the globe from the 
margin of the cornea backward to the entrance 
of the optic nerve, and is connected to it by a 
very delicate connective tissue. Both layers are 
lined on the inner surface by endothelial cells. 
The cavity between them is continuous with 
the space between the two layers of the sheath 
of the optic nerve, w^hich is known as the sub- 
arachnoid space. The inner layer is known as 
the pia mater, and the outer as the dura mater, 
and between them empty the lymphatic vessels 
of the sclerotic. This capsule is penetrated by 
the (tendon) muscles of the eyeball near their 
insertion, which spread out fan shape and are 
attached to the sclerotic. 

Anatomist <a-nat'-o-mist), A person who is skilled 
in anatomy. 

Anatomy of Orbits. See Orbit. 

Anatro'pia (Gr. ana = up + trope = a turning). 
That condition in which the eyes turn up. 

Angle. A figure formed by two straight lines ex- 
tending out from one point in different direc- 


tions. Acute Angle is an angle less than a right 
angle, or less than 90 degrees. Adjacent or 
Contiguous angles are such as have one leg 
common to both angles. Angle Alpha is the 
angle formed by the optic and visual axis. 
Angular Aperture is the angle formed at the 
focal point of a microscope by the most diver* 
gent rays which enter the objective lens. Angle 
of Convergence is the. angle which the two 
visual axes form in turning from their position 
of rest to a point less remote. The angle formed 
by the eyes turning from parallelism until the 
visual axes are directed to a point one meter 
distant on the median line, is called a meter 
angle of convergence and is the unit of the 
angle of convergence. When the visual axes 
meet on the median line, at a half meter dis- 
tance, it is called a two-meter angle of con- 
vergence, and when looking at a third meter 
distance it is called a three-meter angle of con- 
vergence. Critical Angle is the angle beyond 
which a ray of light passing from a higher to 
a less refractive medium cannot emerge. Angle 
of Deviation is the angle formed between the 
direction of the incident and emergent rays, 
and shows the total deflection. Angle of Gamma 
is the angle formed at the center of rotation of 
the eye by the optic axis and a line drawn from 
the point on the object looked at. It varies with 
the refraction of the eye, and in emmetropia is 
about 5°; it increases in hyperopia and 
decreases in myopia. Angle of Incidence is the 
angle formed by the incident ray with the per- 
pendicular at the surface. Angle of Iris is the 
angle between the iris and the cornea at the 

periphery of the anterior chamber of the eye. 
Meter Angle (for description, see under Meter 
Angle). Minute Angle is an angle formed by 
two straight lines that have traveled twenty 
feet distant from a point and separated the 
sixtieth part of a degree. Oblique Angle is an 
angle acute or obtuse, in opposition to a right 
angle. Obtuse Angle is an angle greater than a 
right angle or more than 90 degrees. Optic 
Angle is the angle included between the optic 
axes of the two eyes when directed to the same 
point. Angle of Prism is the angle formed by 
the surfaces of the prism which incline to each 
other. Angle of Reflection is an angle formed 
by the reflected ray with a line perpendicular 
to the reflecting surface, and is always equal to 
the Angle of Incidence. Angle of Refraction is 
the angle formed by the refracted ray with the 
perpendicular. Right Angle is an angle formed 
by a right line falling on another perpendicu- 
larly, or an angle of 90 degrees. Angle of Stra- 
bismus is the angle formed by the deviating eye 
with that of its fellow. Visual Angle is the 
angle formed between straight lines drawn from 
the boundaries of the object looked at and 
crossing the optical center of the eye. 

Anian'thlnopsy (Gr. an — not -f ianthinos = violet 
colored + opsis = vision). Inability to distin- 
guish violet shades. 

Aniridia (an-ir-id'-e-ah). (Gr. an = not + iris.) 
Congenital absence of the iris. 

Anisocoria fan-is-o-ko'-re-ah). (Gr. anisos = un- 
equal -f koro =^ pupil. ) That condition where 
the two pupils are unequal. 


Anisometropia (an-is-o-me-tro'-pe-ah). (Gr. an = 
not, iso ^ equal, metron = measure, ops =- eye.) 
A difference of refraction in the two eyes. The 
defect is usually congenital, but it can be ac- 
quired, as in Aphakia, or operations of any 
kind. One eye may be emmetropic, the other 
hypermetropic, or myopic, or one more hyper- 
metropic, myopic, or astigmatic than the other. 
When one eye is hypermetropic or emmetropic, 
and the other myopic, the hypermetropic or 
emmetropic eye is used for distance, and the 
myopic eye for near-vision. 

Anisopia (an-is-o'-pe-ah). (Gr. an = not, iso = 
equal, ops ^= eye.) An inability of both eyes to 
receive equal impressions, not due to an un- 
equal refractive state. 

Anisosthenic (an-i-sos-then'-ik). (Gr. anisos = un- 
equal + sthenos = strength.) Of an unequal 
strength, as when the muscles of the eyes are 
unequal in power. 

Anisotropous, anisotropal, anisotropic (Gr. anison 
^= unequal + tropos =^ a turning). Producing 
double refraction of a transmitted ray of light. 

Ankyloblepharon (ang-kil-o-blef'-ar-on). Adhesions 
of the edges of the eyelids. 

An'nular Muscle. A ring-shaped muscle (as the 
sphincter muscle of the iris). 

Annulus (an'-nu-lus). A ring-shaped organ. A. 
ci Maris, boundary between iris and choroid. 

Anomaly (a-nom'-a-ly). (Gr, anomalia = irregu- 
larity.) Deviation from normal standard. 

Anoopsia (an-o-op'-se-ah). Where the eye has 
turned upward. (Strabismus.) 


Anophthalmia (an-off-thal'-me-ah). (Gr. an = not 
+ ophthalmos = eye.) Absence of the eyes. 

Anopia (ano'pia). (Gr. an = without + ops = 
eye). Congenital absence of the eye, or eyes. 

Anopsia (an-op'-se-ah). (Gr. an = not + opsis = 
sight.) Disuse of the eye from certain defects, 
such as cataract, amblyopia, and high refractive 

Anorthopia (an-or-tho'-pe-ah). (Gr. an = not + 
orthos = straight + ops =^ eye.) A defective 
state of vision which is unable to distinguish a 
want of parallelism. 

Anterior (front part). Referring to the eye, the 
cornea would be the most anterior point. 

Antimetropia (an-ti-me-tro'-pe-ah). (Gr. anti = 
opposite, metron = measure.) Where one eye 
is myopic and the other hypermetropic. 

Antiseptic (an-ti-sep'-tik). (Gr. anti = against + 
septic = putrid.) A substance which is destruc- 
tive to poisonous germs. 

Aorta (a-or'-ta). (Gr. aeiro = to lift, raise.) The 
great main trunk of the arterial system, pro- 
ceeding from the left ventricle of the heart, 
giving origin to all the arteries except the pul- 
monary (lungs). 

Apex (a'-pex). (L., summit or tip.) The thin edge 
of a prism. 

Aphacia. See Aphakia, 

Aphakia (ah-fa'-ke-ah). (Gr. a = lacking, phakos 
= lens.) Absence of the crystalline lens. 

Aphose (ah-foz'). (Gr. a = without + phos = 
light.) Any visual sensation due to absence or 
interruption of light. 


Apical (a'-pik-al). Pertaining to the apex, 

Aplanatic (ah-plan-at'-ik). (Gr. a = not + plane- 
tos = wandering.) Tliat condition where there 
is neither spherical nor chromatic aberration, 
and the lines are also straight. (See Lens.) 

Aponeurosis (ap-on-u-ro'-sis). (Gr. apo = from + 
neuron = sinew.) A fibrous band investing mus- 
cles and connecting them with tendons. It is 
white, fibrous, and destitute of nerves, and has 
very little blood. 

Apparent Position. The position apparently occu- 
pied by an object seen through a refracting 
medium, as distinguished from its real position. 

Appendages of the Eye are the orbits, the eye- 
brows, the eyelids, the conjunctiva, the lach- 
rymal apparatus, the muscles, the aponeurosis, 
and vessels and nerves of the orbit. 

Applanatio-corneae (ap-lan-a'-she-o-kor'-ne-e). A 
condition in which the cornea becomes flat- 

Applana'tion (L. ad = to + planare = to flatten). 
Flattening of a normally convex surface. 

Approximation (a-prok-si-ma'-shon). (L. ad = to 
-f proximare = to come near.) A continual ap- 
proach to a true result. A result so near the 
truth as to be sufficient for a given purpose. 

Aqueous Humor (a'-que-us hu'-mor). (L. aqua = 
water, humor = moist.) A transparent, watery 
fluid which fills the anterior and posterior 
chambers of the eye, the iris becoming the 
boundary line between the two chambers. 
Weight, 5 grains. Composed of water, albumen, 
and salts. The aqueous is a secretion formed by 


the epithelial cells lining the apices of the cil- 
iary processes, passing through the pupii and 
leaving the eye through Schlemms Canal to pass 
into the anterior ciliary vein. If this humor is 
allowed to escape it will re-form again. Its 
index of refraction is 1.33. 

Aquocapsulitis (,a'-kwo-caps-ii-li'-tis). Serous in- 
flammation of the iris. 

Arachnoid (ar-ak*-noyd). (Gr. arachne = cobweb, 
eidos = resemblance.) Resembling a spiders 

Arachnoid Membrane is a name given to 
several membranes which, by their extreme 
fineness, resemble spider webs. The delicate 
membrane between the dura mater and pia 
maier of the optic nerve and capsule of tenon. 

Subarachnoid Space is located between the 
arachnoid membrane and the pia mater. It 
contains the greater part of the cerebrospinal 

Subdural Space is located between the dura 
mater and the arachnoid membrane, and con- 
tains a small amount of subdui'al fluid. 

The use of the subarachnoid or cerebro-spinal 
fluid is to mechanically protect the nerve cen- 
ters from shock, and to fill tip space, as fat does 
in other parts of the body. Its amount is esti- 
mated at less than two ounces. 

Arc (ark). (L. arciis = bow.) A portion of a 
curved line or segment of a circle. 

Arcus senilis (ar'-kus sen'-il-es). (L. arcus — bow. 
senilis ^- old.) White circle in cornea near 
sclerotic. The arcus is first noticed as two 
small white opaque crescents, one above and the 


other below within the margin of the cornea, 
gradually extending until the ends join, form- 
ing a ring. The arcus will increase in opacity 
more than in width, and the cornea remains 
perfectly transparent within its circle and vision 
is not Impaired by it. Cause, fatty degenera- 
tion. Condition in aged. 

Area of Critical Definition. That portion of an 
optical image within which the detail is clearly 

Argambiyopia (ar-gam-ble-o'-pe-ah). Amblyopia 

from non-use of eye. 

Argyll-Robertson Pupil. A pupil that will not re- 
spond to light, but contracts in accomm.odation. 
Can be seen in locomotor-ataxia. 

Arithmetic fa-rith'-me-tik). (Gr. arithmos = num- 
ber. ) The theory of numbers, the art of com- 
putation, and the applications of numbers to 
science and business. 

Artery (ar'-tery). (Gr. tube.) The vessel which 
carries the purified blood from the heart to the 
different cells of the body. The ophthalmic ar- 
tery supplies the eye with blood and it arises 
from the internal carotid artery at the anterior 
clinoid process and is about one-twelfth of an 
inch in diameter. It enters the orbit through 
the optic foramen below and on the temple side 
of the optic nerve. It then passes over the 
nerve to the inner wall of the orbit and runs 
forward to the inner angle of the eye, where it 
divides into the frontal and nasal branches, 
which may be divided into an orbital group. It 
gives off the lachrymal, supra-orbital, anterior 
and posterior ethmoidal, palpebral, frontal and 

the nasal, muscular anterior, short and long 
ciliary, and the central artery of the retina. 

The short ciliary arteries (six to ten in num- 
ber) enter the eye through the sclerotic around 
the optic nerve to supply the choroid and ciliary 

The long ciliary arteries (two in number) 
pierce the sclerotic, one on each side of the eye, 
and^run forward between the choroid and the 
sclerotic to the ciliary muscles, which they sup- 
ply, and they join the anterior ciliary arteries. 

Th-e anterior ciliary arteries (five to eight in 
number) are derived from the muscular and 
lachrymal branches of the ophthalmic. They 
penetrate the sclerotic about a sixteenth of an 
inch from the corneal margin, and finally join 
the long posterior ciliary arteries to form the 
circulus arteriosus iridis major. 

The arteria centralis retinae is the first and 
one of the smallest branches of the ophthalmic 
artery. It pierces the optic nerve about half an 
inch behind the eye ball and runs forward to 
the retina, in its centre, entering the eye 
through an opening in the lamina cribrosa. 
known as the porus opticus, where it divides 
into four branches. 

Artificial Eye. A thin glass plate which resembles 
the sclerotic, cornea and iris. Artificial eyes 
are made in different sizes and colors, and are 
always fitted to match the sound eye. Before 
inserting the artificial eye it should be put into 
salt and water for a few minutes, then draw the 
upper lid out and down, and slip the eye up 
under; then draw the lower lid out and down, 
and in this way allow the eye to fall into posi- 




tion. As a rule, an artificial eye will last about 
a year, when it begins to lose its smoothness 
and a new one is required. 

Artificial Pupil. One made by an operation 

Asep'sis. Free from septic matter, or free from 

Asthenopia fas-then-o'-pi-ah). (Gr. a = lacking, 
sthenos == strength, ops = eye.) Weak, tired 
and painful vision; the result of straining some 
part of the mechanism of the eye. Vision may 
be normal. It is subdivided into three kinds: 
retinal, muscular, and accommodative. 

Retinal. Where the eye cannot stand light 

without pain; intolerance of light; photophobia. 

IVIuscular. A condition of the eyes in which 

the muscles controlling their movement suffer 

from speedy fatigue, causing pain. 

Accommodative. Fatigue of the ciliary mus- 
cles by hypermetropia, presbyopia, or overwork 
in emmetropia. 

Astigmagraph (as-tig'-ma-graf). An instrument 
used to demonstrate the state or condition of 
astigmatism of the eye. 

Astigmatism (as-tig'-mat-ism). (Gr. a = not + 
stigma = a point.) Astigmatism is a term ap- 
plied to an eye whose refraction is not the 
same in all its parts, causing the eye to focus 
the light at different points. It is subdivided 
into two kinds, regular and irregular. Irregular 
astigmatism is where there is a difference of 
refraction in one and the same meridian, and 
according to some authors, is subdivided into 
normar ana abnormal. Normal irregular astig- 


matism is due in a great measure to irregulari- 
ties in the refracting power of the different 
sectors of the lens, and causes a luminous point 
to appear stellate, or star shape. The abnormal 
variety is usually caused by ulcers, conical cor- 
nea, or injury of the cornea, but the same con- 
dition may be congenital. This kind of astig- 
matism cannot be corrected with lenses. Regu- 
lar astigmatism is where we have the meridians 
of greatest and least curvature at right angles 
to each other, and are known as the principal 
meridians. This variety can be corrected with 
cylindrical lenses. It has five subdivisions, 
which merely serve to show the location of the 
foci, which are as follows: 

No. 1. Compound Hyperopia Astigmatism is 
that condition in which the foci of the two prin- 
cipal meridians are back of the retina at differ- 
ent places when the eye is at rest and looking 
at infinity. 

No. 1. Compound Hyperopic Astigmatism. 

No. 2. Simple Hyperopic Astigmatism is that 
condition in which parallel rays enter the eye. 
and one of the principal meridians focuses on 
the retina, the other behind the retina, when 
the eye is at rest. 



No. 2 Simple Hyperopic Astign^iatism. 

No. 3. Compound Myopic Astigmatism is 
that condition in which the two principal 
meridians focus in front of the retina at differ- 
ent places when the eye is at rest and looking 
at infinity. 

No. 3. Compound Myopic Astig-malism. 

No. 4. Simple Myopic Astigmatism is that 
condition in which one of the principal merid- 
ians focuses on the retina and the other in 
front with the eye at rest and looking at 

No. 4. Simple Myopic Astigmatism. 


No. 5. Mixed Astigmatism is that condition 
in wliich one of the principal meridians focuses 
in front of the retina and the other behind the 
retina when tlie eye is at rest and loolving at 
infinity. It derives its name, mixed astigmatism, 
from tlie fact that one meridian is hyperopic 
and the other myopic. 

No. 5. Mixed Astigmatism. 

Corneal Astigmatism is caused by irregularity 
of the curvature of the cornea. 

Lenticular Astigmatism is caused by an irregu- 
larity of the curvature of the crystalline lens. 

Astigmatism with the Rule is where the axis 
of a minus cylinder that will correct the astig- 
matism is nearer the 180th meridian than the 
90th, or the axis of a plus cylinder that will cor- 
rect the astigmatism is nearer 90 than 180; 
otherwise, it is against the rule. 

Correcting cases of high astigmatism often 
proves unsatisfactory at the time. When the 
image is formed on the retina of such an eye it 
is much blurred at one of the principal merid- 
ians, and sometimes distorted. However, the 
patient accepts this, as his vision has never 
been better. So much so that when the correct 
lenses form a distinct retinal image, he fails to 
recognize it, and will sometimes say that the 


object looks distorted, as the fibers of his optic 
nerve are somewhat amblyopic, and therefore 
different from those of other people. In such 
cases the brain is in the habit of accepting 
vision from parts of the retina that are most 
distinct, and when wearing their correction for 
the first time, the vision shows very little im- 
provement, if any. It is not uncommon for 
cases of say 4-D., of astigmatism to see very 
little better with their glasses at the time of 
fitting, but if they are worn persistently the 
vision is expected to improve in a few months. 

Astigmom'eter. An instrument for measuring 

Astig'mometry. The study of measurement of 

Astringent (as-trin'-jent). (L. astringere = to 
contract.) An agent that causes contraction 
and arrests discharges. 

Asymmetry (ah-sim'-et-re). (Gr. a = not + syn = 
with + metron = measure.) When the eyes do 
not correspond, or resemble each other in 
appearance, they are said to lack symmetry. 

Atax'ia. (Gr. a = not + taxis = order.) Failure of 
muscles to coordinate. 

Atom (at'-om). (Physics.) An ultimate indi- 
visible particle of matter. 

Atonic (aton'-ic). (Gr. atonia = languor.) Relaxed; 
without normal tone or tension. 

Atrophy. (Gr. a = not -f trope = nourishment.) A 
wasting away of a part from a lack of nutrition. 

Atropine (at'-ro-pin). A poisonous alkaloid ex- 
tracted from atropa-belladonna, or deadly night- 


shade; it temporarily paralyzes the sphincter 
iridis (circular muscles of the iris) and the 
ciliary muscles within the eye, consequently the 
pupil is dilated and accommodation fully re- 
laxed, leaving the eye adjusted for its far point 
of vision in a state of rest. For this reason it 
is known as a mydriatic and a cycloplegic, and 
is used more than any other to suspend accom- 
modation and dilate the pupil. Atropine para- 
lyzes the sphincter muscle of the iris and the 
ciliary muscle, and hence results in dilatation of 
the pupil, and also an inability to see clearly 
near by. The dilatation of the pupil is a maxi- 
mum one. If, in the case of a dilatation of the 
pupil caused by oculomotor paralysis, atropine 
is instilled, the pupil becomes still more dilated. 
This proves that atropine, besides producing 
paralysis of the contracting fibers, causes also 
stimulation of the dilating fibers. The effect of 

. the atropine makes its appearance in from ten 
to fifteen minutes after the instillation, and 
soon reaches its maximum. Commencing with 
the third day it begins to decrease again, but 
does not disappear completely until after the 
lapse of a week. The instillation of atropine, 
therefore, causes the patient a disturbance of 
rather long duration, and hence should be em- 
ployed only when there is good reason for it. 

Atropinism (at'-ro-pin-ism). A condition produced 
by the use of atropine. 

At'ropinize. To put under the influence of 

Atypic Hypermetropia (at-ipMk). Irregular Hyper- 
metropia caused by tumors behind the eye, ex- 
erting such a pressure on the posterior pole 


that the region of the macula is pushed in front 
of the principal focus, the eye thus becoming 
hyperopic. It may be caused by detachment of 
the retina in the region of the macula. 

Atypic Myopia (at-ip'-ik). Progressive Myopia, 
caused by the elongation of the eye. 

Autophthalmoscope (au-tof-thal'-mo-skope). An 
ophthalmoscope planned in such a way that a 
person can examine his own eyes. 

Average (av'-e-raj). Etymology obscure. The re- 
sult of adding several quantities and dividing 
the sum by the number of quantities. 

Avoirdupois (av'-or-du-poiz'). (Fr. aver = goods -f 
de = of = pois = weight.) A system of weight 
in which 1 lb. = 16 oz. = approximately 7,000 
troy grains. 

Axial. Of, or pertaining to, an axis. 

Axial Ametropia. Ametropia that is caused by 
the length of the eyeball on the optic axis. 

Axially. In the direction of the axis. 

Axiom (ak'-si-om). (Gr. axioma ^ a requisite, a 
self-evident principle.) A simple statement, of 
a general nature, so obvious that its truth may 
be taken for granted. 

Axis (aks'-i&). A straight line, real or imaginary, 
passing through the center of a body, on which 
it may revolve. 

Optic A. An imaginary line through all cen- 
ters of the eye from before back; that is, the 
center of the cornea, through the nodal points 
to the inner side of the macula lutea. 

Visual A. A line from the macula lutea 
through the optical center of the eye to the 
point on the object looked at. 


Major A. The longest diameter of the cornea 
or lens. Minor A the shortest. 

Principal A. A line which passes through the 
optical center of a lens at right angles to both 
sides, it is the only ray of light to pass through 

Secondary A. Any line crossing the principal 
axis at the optical center. These rays are re- 
fracted, but emerge in the same direction as 
they entered. 

Axis of a Cylinder. The only meridian of a 
cylindrical lens without focusing power. 

Axis of Mirror. A line which strikes the cen- 
ter of curvature at right angles to the surface 
is called its axis. 

Axis of Refraction. The normal to the surface 
of a refracting medium at the point of incidence 
of a ray of light. 
Axometer (ax-om'-e-ter). An instrument for the 
determination of the axis and focus of spherical, 
cylindrical or sphero-cylindrical lenses. 


ACILLAR LAYER (bas'-il-ar). The layer of 
rods and cones of the retina. 

Barom'-eter. (Gr. baros = weight + metron = 
measure.) An instrument indicating the atmos- 
pheric pressure. 

Basalis Lamina, or membrane of Bruch. The 
membrane which separates the ghoroid from the 
pigmentary layer of the retina. 

Base. (L. bassus = low.) (a) The line or surface 
forming that part of a figure on which it is sup- 


posed to stand, (b) The base of a system of 
logarithms is the number which, raised to the 
power indicated by the logarithm, gives the 
number to which the logarithm belongs, (c) In 
percentage, the number which is multiplied by 
the rate to produce the percentage. The base 
of a prism is its thickest part. 

Base Apex Line. A straight line drawn from the 
thickest to the thinnest part of a prism. 

Base Curve. The meridian of least refraction, on 
the toric side of a lens. 

Basedow's Disease. (See exophthalmic goiter.) 

Beer's Knife. A knife with a triangular blade for 
corneal incision. 

Bi. (L. bis = twice.) Is employed to signify two 
things in one; for instance, bifocal, biconcave, 

Biconcave. Concave on both sides. 

Biconvex. Convex on both sides. 

Bifocal (bi-fo'-.'^al). Having a double focus. A 
lens with two focal lengths, having two parts, 
the upper for distance and the lower for near 
vision. They can be made up in five different 
ways, namely: 



One-piece Bifocal. 



Split or Franklin Bifocal 



Perfection Bifocal. 



Cemented Bifocal. 



Invisible Bifocal. 


The one-piece bifocal is made of glass with 
the same density throughout. Its double focus 
is governed by change of curvature. It can be 
mounted with or without rims. The split or 
Franklin and perfection bifocals must be worn 
in rims, while the cemented and also invisible 
bifocals can be worn without rims. The in- 
visible bifocal lenses are made by fusing under 
intense heat, two pieces of curved glass with 
different densities. A bifocal lens consists of 
two parts of two different foci. In hypermet- 
ropia with presbyopia, or old sight, the upper is 
the weaker for distance, the lower being 
stronger for near objects. In myopia, the upper 
should be the stronger and the lower the weaker 
glass. In this way the patient has good distant 
vision without the extra strain on the accom- 

Canada Balsam is used in cementing bifocal 
lenses in the following manner: First be sure 
that the lenses are perfectly clean. Then 
squeeze a small drop of the balsam on to the 
large lens, and press the scale upon the balsam 
until it spreads out thoroughly between the 
glasses, being careful not to break the lenses. 
Then place the lenses on a piece of metal over 
a small flame, and heat them slowly until all 
the bubbles disappear, and until the balsam is 
nearly hard — just about hard enough to take a 
slight impression of the finger nail. It is impos- 
sible for a novice to accurately judge just how 
much to heat the lenses, but with practice it 
becomes a simple matter. The success depends 
largely on their being heated just long enough. 
If they are not heated enough they will slide 


out of position, and if they are heated too much 
they will chip off very easily. 

Binocular. (L. bis = twice, oculus ^ eye.) Per- 
taining to both" eyes. In vision it refers to the 
ability of both eyes to see the same point of an 
object at the same time. To prove it exists a 
5° prism placed base up or down over one eye 
should make the object looked at appear double. 

Biorbital Angle. The same as the optic angle. 

Birefractive. Doubly refractive. 

Bl-Spherical. A lens with a sphere on both sides. 

Blear-eye. Marginal blepharitis. 

Blennorrhea (blen-or-e'-ah). (Gr. blennos = mu- 
cus + rhoia = a flow.) Excessive mucous dis- 

Blepharadenitis (blef-ar-ad-en-i'-tis). (Gr. bleph- 
aron = eyelid + aden = gland + itis.) Inflam- 
mation of the meibomian glands. 

Blepharal (blef'-ar-al). (Gr. blepharon = eyelid.) 
Pertaining to the eyelids. 

Blepharelosis (blef-ar-el-o'-sis). Ingrowing eye- 
lashes. (See Trichiasis.) 

Blepharism (blef-ar-ism). Where there is an in- 
ability on the part of 4;he patient to refrain from 
winking. (Blinking.) 

Blepharitis (blef-ar-i'-tis). (Gr. blephron = eye- 
lid + itis = inflammation.) Inflammation of the 
eyelids. Ciliaris or marginalis b. That condi- 
tion where the hair follicles of the eyelid are 
inflamed. Squamosa b. A marginal blepharitis 
in which the edges of the lids become scaly. 
Uncerosa b. An ulcerous form of marginal 


Blepharochalasis (blef'-ar-o-kal'-as-is). (Gr. bleph- 
aron = eyelid + chalasis = a slackening.) Re- 
laxation of the skin of the eyelid, due to atrophy 
of the intercellular tissue. A condition in which 
folds of the skin hang down. 

Blepharoclonus (blef-ar-ok-lo-nus). (Gr. bleph- 
aron — eyelid + klonos = a tumult.) Clonic 
spasm of the eyelids. 

Blepharoconjunctivitis. Inflammation of the eye- 
lids and conjunctiva. 

Blepharoncus (blef-ar-ong'-kus). (Gr. blepharon = 
eyelid + onkos = a tumor.) A tumor or swell- 
ing of the eyelid. 

Blepharoplegia (blef-ar-o-ple'-ge-ia). (Gr. bleph- 
aron ^ eyelid + plege = stroke.) That state in 
which the eyelid is paralyzed, causing ptosis. 

Blepharoptosis (blef-ar-op-to'-sis). (Gr. blepharon = 
eyelid + ptosis = a falling.) That condition 
where the upper eyelid droops from paralysis. 

Blepharopyorrhea. (Gr. blepharon =^ eyelid + 
pyon = pus + rhoia = I flow.) A discharge of 
mucus from the eyelids. 

Blepharorrhaphy ( blef-ar-or'-af-e). (Gr, bleph- 
aron = eyelid + rhaphe = seam.) The stitch- 
ing together of a part of the edges of a slit 
between the eyelids. 

Blepharospasm (blef'-ar-o-spasm). A spasmodic 
contraction of the orbicularis palpebrarum mus- 
cle, so that the lids are firmly pressed against 
the globe. Occurs where photophobia is marked. 
It is reflex from the irritation of the fifth nerve, 
and occurs in neuralgia of its branches; in 
inflammation of the conjunctiva or cornea; from 
foreign bodies; errors of refraction, etc. 


Blepharostat (blef-ar'-o-stat). (Gr. blepharon = 
eyelid -f- states = fixed.) An instrument used 
for holding the eyelids apart. 

Blepharostenosis (blef ar-o-ste-no'-sis). Gr. 
blepharon = eyelid + stenosis = a narrowing.) 
A narrowing of the palpebral slit between the 

Blepharosynechia (blef-ar-o-sin-ek'-i-a). (Gr. bleph- 
aron = eyelid + synechia = continuity.) A con- 
dition in which there is a growing together of 
the eyelids. 

Blepharotomy (blef-ar-ot'-o-me). (Gr. blepharon = 
eyelid + tome =^ incision.) A surgical opera- 
tion for the cutting of the eyelid. 

Blind. Loss of sight. Day-blindness is where 
vision is better at night. Night-blindness is de- 
fective vision at night-time. 

Blind Spot. Also known as the optic disc, or 
optic papilla. It marks the entrance of the 
optic nerve on the retina. Not sensitive to light. 

Blinking. That condition in which there is an 
involuntary winking. 

Blood (blud). A red. slightly translucent fluid 
which circulates in the p^i'incipal vascular sys- 
tem of animals, carrying nourishment to all 
parts of the body, and bringing away wa.ste 
products to be excreted. In the veins its color 
is somewhat darker, owing to the loss of oxygen 
while passing through the tissues. 

Blood Vessels. (See veins and arteries.) 

Bonnet's Capsule. The same as Tenon's Capsule. 

Bowman's Membrane. The second anterior layer 
of the cornea. 



Brachymetropia (brach-e-me-tro'-pe-a). (Gr. bracli- 
us =^ short, metron ^^^ measure, ops -= eye.) The 
same as myopia and hypometropia. It is an 
eye where parallel rays of light will focus in 
front of the retina with the muscles of accom- 
modation at rest. 

Brain. The organ of intellect. A nervous mass 
within the skull divided into many parts. 

Brow-Ague. Supra-orbital neuralgia; a superficial 
pain in the region of distribution of the first 
division of the fifth nerve. 

Bruch's Glands. The lymph-follicles of the con- 
juctiva of tlie lower eyelid. 

Bruch's Membrane. The inner layer of the choroid 
coat of the eye. 

Bruch's Muscle. (See Cilfary Muscle.) 

Buphthalmia (buf-thal'-me-ah). (Gr. bous = ox -f- 
ophthalmos ^- eye.) Enlargement of the eye. 

Buphthalmus. (See Buphthalmia.) 

^AMPIMETER (kam-pim'-e-ter). (L. campus = 
field + Gr. metron — ^ measure.) An instrument 
for measuring the field of vision, replaced by 

Canada Balsam. A liquid resin obtained from the 
balsam-fir tree, which grows in Canada. It is 
used for the purpose of cementing lenses to- 
gether. It is easily melted if heated, and readily 
soluble in alcohol. (See bifocal for its use.) 
Index of refraction 1.52. 

Canallc'ulus. A small canal or channel. 


Canal of Cloquet. The name given to Stilling's 
Canal after Jules Germain Cloquet, Parisian 
surgeon, 1790-1883. 

Canal of Petit. The space which surrounds the 
crystalline lens between the suspensory liga- 

Canal of Schlemm. Circular canal surrounding 
the eye at sclerocorneal junction. (See 

Canal of Stilling. The canal which runs through 
the vitreous humor from the entrance of the 
optic nerve to the posterior surface of the lens. 
It is lined by the hyaloid membrane. This 
canal is said to convey the minute artery from 
the central artery of the retina to the back of 
the lens, during development of the eye. The 
artery then disappears, but the canal remains. 
It is also known as the Hyaloid Canal. 

Canals of Fontana. A number of little spaces or 
openings between the iris and cornea, in the 
sclerotic. (See Spaces of Fontana; also see 
Schlemm's Canal.) 

Cancel (kan'-sel). (L. cancelli = a lattice.) Orig- 
inally to draw lines across a calculation. To 
strike out or eliminate as a common factor in 
the terms of a fraction, a common term in the 
two members of an equation, etc. 

Canthectomy (kan-thek'-to-my). (Gr. kanthos. 
canthus + ektome = excision.) An operation in 
which part of the canthus is cut away. 

Ca nth itis (kan-thi'-tis) . Inflammation of the angles 
of the eyelids. 

Cantholysis. (Gr. kanthos, canthus + lysis = 


loosening.) Incision of the canthus to widen the 
slit between the lids. 

Canthoplasty (kan'-tho-plas-te). A surgical opera- 
tion for lessening the pressure and friction of 
the upper lid by cutting the outer canthus. 
Plastic c. operation, an operation for restoring a 
lost part. 

Canthotomy (kan-thot-'o-me). An operation for 
the slitting of either canthus. 

Can'thus. (Gr. "angle of the eye.") The angle 
at the junction of the eyelids, known as the. 
inner and outer canthi. 

Cap'illary (hair like). Any one of the little ves- 
sels which conduct the blood from the arteries 
to the veins. 

Capsule (kap'-sule). (J^. capsula = a box.) A sac 
which encloses an organ for the purpose of 
support, protection and lubrication. The cap- 
sule of the eye lens. 
Capsule of Tenon. (See Tenon's Capsule.) 
Capsulitis (kap-su-li'-tis). Inflammation of the 
capsule of the crystalline lens. 

Capsulotomy (kap-su-lot'-o-my). An operation for 
the cutting of a capsule, as that of the lens. 

Cardinal Points (that on which a thing turns or 
depends). Points which play an important part 
in the course of light through a spherical sur- 
face. There are four in number. The two prin- 
cipal foci and the two nodal points. The first 
principal focus is the point from which light 
rays emanate and pass through a spherical lens 
and emerge parallel to its principal axis. The 
second principal focus is the point where the 


emergent rays cross each other when the inci- 
dent rays have been parallel to the principal 
axis. (See Nodal Point.) 

Carotid (ka-rot'-id). (Gr. karos = deep sleep, 
stupor; so named from the effect of pressing 
on them.) The carotid arteries or carotids are 
the two great arteries of the neck, that convey 
the blood from the aorta to the head, brain and 
eye. The common carotids, one on either side 
of the neck, divide into an external and an 
internal branch, the former supplying the ex- 
terior of the skull. 

Cartilage (kar'-til-aj). (L. Cartilago = gristle.) 
The gristle or white elastic snbstEUice in differ- 
ent parts of the body. (See Tarsus.) 

Cartilaginous (kar-til-aj'-in-us). Relating to or 
consisting of cartilage. 

Caruncula Lachrymalis (kar-un'-ku-.'ah). (L. a 
small fleshy mass. L, lacrima = a tear.) Is the 
small reddish body at the inner canthus of the 

Cast. A cast in the eye would apply to strabismus. 

Cataplioria (kat-a-fo'-re-ah). (Gr. kata = down, 
phoria == "tending.") That condition in which 
one of the eyes, though parallel with its fellow 
when in use, turns downward when the extrin- 
sic muscles are in a state of rest. Esocataphoria 
is the tendency of the visual line inward and 
downward. Exocataphoria is a tendency of the 
visual line outward and downward. 

Cataract (kat'-ar-akt). (Gr. kataraktes — to break 
down.) Any opacity of the crystalline lens or 
lens capsule of the eye. Lenticular c, an 
opacity of the lens proper. Capsular c. an 


opacity of the lens capsule. Senile c, an opacity 
of the lens due to age.. Traumatic c, a catar- 
act due to an injury. Pyramidal c, an opacity 
in the center, yet at the anterior pole, of the 
lens. Secondary c, a cataract appearing after 
the extraction of the lens, caused by that part 
of the lens capsule still attached to the hyaloid 
membrane becoming opaque. Cortical c, that 
condition in which the border or outer layers of 
the lens are losing their transparency. Hard c. 
(See Senile c). Soft c, where the lens is soft 
and milky. Polar c, an opacity confined to the 
anterior or posterior pole of the lens. 

Catacaustic. (See Caustic surface.)^ 

Cat'adioptrical. (Physics.) Pertaining to, pro- 
duced by, or involving, both the reflection and 
refraction of light. 

Catopter (kat-op'-ter). (Gr. kata = down + opto- 
mai = I see.) A reflecting optical glass or in- 
strument; a mirror. 

Catoptric (kat-op'-trik). Relating to that branch 
of optics called catoptrics; pertaining to inci- 
dent and reflected light. The whole doctrine of 
catoptrics is founded on this simple principle 
that the angle of reflection is equal to the angle 
of incidence. 

Catoptric Test (kat-op'-trik). A test for cataract 
by light reflected from the crystalline lens. In 
this test ask the patient to look straight ahead, 
then hold a lighted candfe about twelve inches 
in front of the eye, a little to one side, while 
you stand slightly on the other and look into 
his pupil. If there is no opacity of the lens or 
capsule you will notice three images of the can- 


. die. The first will be on the surface of the 
cornea in an upright position, the second will 
be on the anterior surface of the lens, also up- 
right, while the third will be inverted and much 
smaller on the posterior surface of the lens, but 
when there is a cataract you will fail to find the 
inverted image (known as Pyrkinges Images). 

Catoptry (kat-op'-tre). The unit of reflective 
power of curved mirrors. A mirror that will 
reflect parallel rays of light to a point of focus 
at a distance of one meter. 

Cat's-eye Pupil. Where the pupil of the eye is 
long and narrow (slit-like). 

Caustic Curve (kaus'-tik). A curve to which the 
raj^s of light reflected or refracted by another 
curve are tangent. 

Caustic Surface. A surface to which rays of light 
reflected or refracted by another surface are 
tangents. Caustic curves are called catacaustic 
when formed by reflection and diacaustic when 
formed by refraction. 

Cellulitis (sel-u-li'-tis). Inflammation of the loose 
tissues of the orbit. 

Center (of curvature). If the surface of a lens 
were completed so as to form a circle, its center 
would be the center of curvature. (See Optical 

Centimeter (sen'-tlm-e-ter). One-hundredth part 
of a meter. 

Centrad (sen'-trad). Toward the center; unit of 
measurement for prisms which will produce a 
deviation in a ray of light one-hundredth of a 


iLentric (sen'-trik). Pertaining to a nerve center. 
Centrifugal (sen-trif'-u-gal). Tending, or causing, 

to recede from tlie center. 
Centrifugal Impression. An irnpression sent from 

a nerve center outwards to a muscle or muscles 

by which motion is produced. 
Centrophose. (Gr. kentron = center + phos = 

light.) A subjective sensation of a light spot or 

patch, the cause being located in the optic brain 

Ceratitis (ser-at-i'-tis). (Gr. "horn" + suffix, itis = 

inflammation.) The same as keratitis. 

Ceratonosus (ser-at-on'-o-sus). (Gr. keras = 
horn + nosos = disease.) Any disease of the 

Ceratotome (se-rat'-o-tom). A knife for dividing 
the cornea. 

Chalazion (chal-a'-zi-on). (Gr. "Hail.") A tumor 
on the eyelid. On the under surface of the 
tarsal plate of the upper and lower lid are 

- numerous creases or depressions running at 
right angles to the margin of the lid. There 
are about thirty of them in the upper lid and 
about twenty in the lower? In these depres- 
sions are small tubular glands, called meibomian 
glands, and their ducts open next to the margin 
of the lid. A chalazion is an enlargement of 
one or more of these glands, due to the stop- 
page of their ducts, and is usually chronic in 
character. A chalazion is also called a tarsal 
tumor, tarsal cyst, or meibomian cyst, etc. It is 
not a true retention cyst, but its contents may 
soften so that it will become an encysted 
abscesb. At first its contents are gelatinous, 


but later may become purulent. The tumor is 
firm, round, with the skin moving freely over 
the mass, but it is firmly attached to the tarsal 
plate. It has so much the appearance of a seba- 
ceous cyst that one is liable to be mistaken in 
the diagnosis, unless he is familiar with the 
disease. Usually chalazion tends toward the 
conjunctiva, and, if the lid is everted, the posi- 
tion of the tumor may be located by a bluish 
discoloration, or, if the contents are purulent, 
a yellowish discoloration. The primary cause 
of this trouble is not definitely known, but a 
debilitated condition of the system, eye-strain, 
and blepharitis marginalis seem to be the fac- 
tors in producing chalazion. 

Chamber. (Gr. "vaulted room.") The spaces of 
the eye. A term used in speaking of the eye, 
in which there are three chambers. The an- 
terior c. is the space between the cornea and 
the front surface of the iris; the posterior c, 
the space between the iris and the front sur- 
face of the lens capsule. These two are filled 
with the aqueous humor and communicates 
through the pupil; vitreous c, the space sur- 
rounded by the hyaloid membrane behind the 
lens, occupying four-fifths of the globe of the 

Chemosis (ke-mo'-sis). (Gr. "an aperture" and 
suffix osis, signifying "morbid condition.") A 
swollen condition of the conjunctiva, forming 
an elevated ring around the cornea. 

Chiasm (ki'-asm). (Gr. chiasma = two crossing 
lines.) A crossing; especially the crossing of 
the fibers of the optic nerve (optic commissure). 


Chiastometer (ki-as-tom'-e-ter). An instrument 
for ascertaining the deviation of the optic axis. 

Chlorophane (klo'-ro-fan). (Gr. chloros = green- 
ish yellow + phaino = I show). A green-yellow 
pigment from the retina. 

Chloropsia. (Gr. chloros = yellowish green + 
opsis = eyesight). Green vision. A condition 
in which all objects appear to be colored green. 

Choked Disc. Congested arid inflamed state of 
the optic disc. 

Chondral (kon'-dral). (Gr. chondros = cartilage.) 
Pertaining to cartilage. 

Chorea (ko-re'-ah). (Gr. choreia = choral dance.) 
St. Vitus' dance. A disease of the nervous sys- 
tem, characterized by a succession of irregular, 
clonic involuntary movements, of limited range 
occurring in almost all parts of the body. Con- 
trol of the muscles is not lost, but voluntary 
motions are interfered with by the involuntary 

Chorioid. See Choroid. 

Choroid (ko'-roid). "Skin-like bag with multitude 
of blood vessels." That part of the second tunic 
of the eye extending from the optic nerve en- 
trance to the posterior limit of the ciliary body. 
It is covered by the retina on the inner side. 
It constitutes the posterior two-thirds of this 
tascular tunic. Its thickness gradually dimin- 
ishes toward the ciliary body. The choroid 
consists of a compact mass of connective tissue, 
stroma, which supports the numerous blood 
vessels of varying size; forming three layers. 


1. The layer of stroma containing large blood 

2. The chorio-capillaris. 

3. The membrana vitrea. 

The first layer is the most conspicuous of the 
three, for its large blood vessels emerge into 
four main trunks, the vena vorticosae; these 
pierce the sclerotic at equal distances apart, 
running obliquely backward. The nerves of the 
choroid are derived from branches of the long 
and short ciliary nerves. Its blood supply is 
fi-om the short posterior, long posterior and 
anterior ciliary arteries. The red reflex seen 
in the eye when viewed with the retiiioscope 
and ophthalmoscope is due to the reddish color 
of the blood vessels in the choroid showing 
through the retina. 

Choroidal Fissure. The opening in the choroid 
through which the optic nerve passes to form 
the retina. 

Choroideremia (ko-roi-de-re'-me-ah). Absence of 
the choroid. 

Choroiditis (ko-roi-di'-tis). Inflammation of the 

Choroidocycli'tis. Inflammation of the choroid 
and ciliary processes. 

Choroidoiritis (ko-roi-do-i-ri'-tis). Inflammation of 
the choroid and iris. 

Choroidoretini'tis. Inflammation of the choroid 
and retina. 

Chromatic (kro-mat'-ik). (Gr. chroma = color.) 
Relating to color. 

Chromatic Aberration. See Aberration. 


Chromatodysopia (kro-mat-o-dys-o'-pi-ah). (Gr. 
chroma ^ color + dys ---=^ bad + ops == eye.) Col- 

''/hromatogenous (kro-mat-oj'-en-us). (Gr. chroma 
= color + gennao = I produce.) Producing color. 

Chromatology (kro-mat-ol'-o-gy). The study of 

Chromatom'eter. An instrument for measuring 
color or color perception, 

Chromatophobia (kro-mat-o-fo'-be-ah). (Gr. chro- 
ma = color + phobos = fear.) An abnormal 
fear of color. 

Chromatopsia (kro-mat-op'-se-ah). (Gr. chroma = 
color + opsis = vision.) Abnormal sensation 
of color, due to disorders of the optic centers, 
or to drugs, especially santonin. 

Chromatoptometry (kro-mat-op-tom'-et-ry). Tak- 
ing the measurement of the power of color per- 

Chromometer (kro-mom'-et-er). An instrument for 
measuring coloring matter present. 

Chromoptometer (kro-mop^tom'-et-er). An instru- 
ment to test the color sense. 

Chromoscope. (Gr. chromo = color + skopeo = I 
view.) An apparatus for testing the color sense. 

Cibisitome (sib-is'-it-om). An instrument for in- 
cising the lens capsule. 

Cilia. (L. cilium = eyelash.) The eyelashes. 

Ciliariscope (sil-i-ar'-is-cope). An instrument for 
examining the ciliary region of the eye. 



Ciliary (sil'-i-a-ry). Pertaining to, or like, the eye- 

Ciliary Body. The middle part of the second tunic, 
composed of ciliary processes, ciliary veins, 
ciliary muscles, ciliary nerves and arteries. 

Cut showing Choroid. Ciliary Body. Iris and Xerves. 

Ciliary Processes. The radiating circular folds 
composed of a connective tissue stroma.' which 
pass up over the ciliary body. There are about 
sixty or seventy in number. 

Cillo (cil'-lo) or Cillosis. (Gr. "I move.") A 
trembling or spasmodic twitch of the eyelids. 

Cinerea (sin-e'-re-ah). (L. cinereus = ashy.) The 
gray matter of the nervous system. 

Circle (sir'-kl). (L. circulus, dim of circus. Gr. 
kirkos — a ring.) A plane figure whose periphery 


is everywhere equally distant from a point 
within it, the center. 
Circles of Haller. Venous and arterial circles of 
the eye. 

Circulation fo^r-cu-la'-shun). (L. circulare = to 
encompass.) The passage of blood in going 
from and returning to the heart after having 
made a circuit of the body. 

Circum. (L. around.) A prefix denoting a circu- 
lar movement, or a position surrounding the 
part indicated by the word to which it is joined. 
Circumlental, surrounding the crystalline lens; 
circum ocular, around the eye; circumorbital, 
around the orbit. 

Circumference (ser-kum'-fe-rens). (L. circum = 
around + ferre = to bear.) The line which 
bounds a circle. 

Clonic Spasm. (Gr. commotion.) An intermittent 
involuntary contraction of a muscle, which 
shows itself when the muscle is in use. 

Cobalt. A hard, brittle, and heavy metal whose 
compounds afford pigments. The Cobalt-blue 
test glass being named after the blue pigment. 
Cobalt-Blue Glass contains a great deal of 
red, and allows only the blue and red rays of 
the spectrum to pass through, neutralizing the 
other five colors contained in white light. It 
is used in testing the ametropia when the pa- 
tient is not color blind. 

Cocaine (ko-ka'-in). A local anaesthetic and mydri- 
atic. Cocaine dilates the pupil, and hence would 
seem to call for mention in this place, although, 
strictly speaking, it does not belong to the 
mydriatics proper — that is, the dilatation of the 


pupil by cocaine is not produced, as in their 
case, by its action upon the contracting or the 
dilating fibers of the iris, but by a contraction of 
the blood vessels of the iris. The dilatation of the 
pupil is therefore only a moderate one, and the 
reaction of the pupil to light persists; moreover, 
mydriatics and miotics still produce an effect. 
If cocaine is instilled into an eye the pupil of 
which has been dilated by atropine, the dilata- 
tion increases somewhat in consequence of the 
anaemia of the iris which then ensues; hence 
the mydriasis produced by the simultaneous 
action of atropine and cocaine is the most com- 
plete that can possibly be attained. The ac- 
commodation is not paralyzed by cocaine, but 
only somewhat weakened. 

Cohesion (ko-he'-shun). (L. con = together + 
haereo = to stick.) That form of attraction by 
which the particles of a body are united 
throughout the mass, whether like or unlike. 

Colmascope (cor-ma-scope). An instrument for 
the detection of strains and stresses in lenses, 
either mounted or unmounted, as a result of 
undue tightening of screws or imperfections in 

Collyrium (col-lyr'-i-um). (Gr. kollyrion = an 
eyewater.) Any lotion to be dropped in the eye. 

Coloboma (kol-o-bo'-mah). (Gr. koloboma := an 
imperfection.) A tear or break in the eyeball, 
as in the iris or choroid. 

Color-Blindness (Achromatopsia). Blindness for 
one or more colors. Due to the absence from 
the retina of one or two of the three primary 
substances (according to Hering). The test is 


liiade by presenting the patient with samples of 
different colored yarns — a number of each color, 
but different shades — and the patient is re- 
quested to separate them. Persons having this 
anomaly of vision are generally unaware of it 

Commissure (kom'-mis-ur). (Optic.) (L. com- 
mittere, "to unite.") The x-like crossing of the 
optic nerves. 

Composite Number (kom-poz'-it). (L. com = to- 
gether -f- ponere = to put.) A number which 
can be exactly divided by a number exceeding 

Compound Lens. A lens that contains a sphere 
and 8. cylinder. 

Com us (ko'-mus). A cone. A crescentic patch of 
atrophic choroid tissue near the optic papilla in 

Concave. (L. concavus = hollow.) Hollow and 
curved or rounded. The opposite to convex. 

Concavo-convex. Concave on one side and convex 
on the other. If the convexity exceeds the con- 
cavity it is known as a periscopic convex lens. 
If the concavity exceeds the convexity it is 
known as a periscopic concave lens. 

Concentric (kon-sen'-tric). (L. con == together -f- 
centrum = center.) That which has a common 
center with. something else. 

Concentrlcal (tri-kal). Having a common center, 
as circles of different size, one within another. 

Concomitant (kon-com'-it-ant). (L. concomitare = 
to accompany.) Accompanying. Concomitant 
Squint is a condition where the two eyes devi- 


ate, but accompany one another in their move- 
ment. The object can be seen by either eye, 
but not the two eyes at the same time. 

Cone (kon). (Gr. konos = peg.) The elementary 
form considered in arithmetic is a solid gen- 
erated by the revolution of a right-angled tri- 
angle about one of its sides as an axis. 

Cone Muscle Test. This consists of a cone 
cemented to a ground glass disc, and is used as 
follows: It is inserted into one cell of trial 
frame in front of the correction for the ametro- 
pia, which must be properly centered as to 
pupillary distance, and a solid blank disc is put 
into the cell in front of the other eye. • The 
patient's attention is then directed to a light 
(preferably a candle or small gas light) twenty 
feet away; and the action of the cone is such 
that the light will resolve itself into a circle of 
light. The other eye is then uncovered, and if 
there is no muscular error the light will appear 
in the center of the circle. If there is muscular 
error the light will be either above or below or 
to one side of center, and can be brought to 
center by the proper prism with base in proper 
position. This does away with necessity for 
computations where there is combined prismatic 
error in different angles, and gives at once the 
position of the base of the correcting prism. 
(See Muscular Imbalance.) 

Conical (con'-ic-al). That which is round and 
tapering to a point. 

Conical Cornea. A cone-like protrusion of the 
cornea anteriorly due to increased intraocular 
pressure and weakening of its central portion. 


Many forms of operations have been suggested 
and while some have been of slight benefit, no 
complete cure is known. Vision can usually be 
improved by means of an opaque disc with an 
opening in its center and worn as an eye glass. 
(Same as Keratoconus.) 

Conjugate. (L. con = with -f jugare = to join.) 
Coupled. To yoke together. 

Conjugate Deviation. The deviation of both eyes 
in the same direction. 

Conjugate Foci (kon'-ju-gat). Two points so situ- 
ated in relation to each other that the direction 
of a ray proceeding from either of them, after 
reflection or refraction, passes through the 
other. Secondary c. A conjugate foci formed 
on a secondary axis. 

Conjunctiva (kon-junc-ti'-va). (L, con = with + 
jungere = to join together.) The mucous mem- 
brane of the eye. It covers the anterior sur- 
face of the eye, passing backward about one- 
half inch, where it turns (fornix) to line the 
inner surface of the eyelids, thus forming a 
complete sac when the eyelids are closed. It 
consists of two portions; the ocular portion, 
which covers the sclerotic, and the palpebral 
portion, which lines the inner surface of the 
lids. The ocular portion is loosely connected 
with the sclerotic, but firmly attached to the 
edge (limbus) of the cornea. The palpebral 
portion is thick, opaque, highly vascular, and 
covered with numerous papillae. At the margin 
of the lids, it becomes continuous with the lin- 

• ing membrane of the ducts of the meibomian 
glands. At its outer and upper angle there are 


from seven to ten ducts through which the tears 
pass from the lacrimal glands. It receives its 
blood supply from the palpebral and lacrimal 
arteries. Its vein, the post-tarsal, is tributary to 
the ophthalmic vein. It receives its nerve sup- 
ply from the fifth pair entering at the inner and 
outer angle of the orbit. 

Conjunctivitis (kon-junc-tiv-i'-tis). Inflammation 
of the conjunctiva. 

Convergence (kon-ver'-gence). (L. con = with + 
vergere = to turn.) The act or power of turn- 
ing the eyes from their position of rest. 
When the eyes are emmetropic and ortho- 
phoric, the two functions, accommodation and 
convergence, work together, yet their objects 
are totally different, but their harmonious co- 
operation is none the less essential. The func- 
tion of accommodation is the focusing of the 
rays of light, on the retina of each eye singly, 
which come from objects looked at within 20 
feet from the eye; while the function of con- 
vergence is the turning of the eye so that the 
image of the object looked at will fall on corre- 
sponding parts of the retina in each eye. For a 
pair of normal eyes to view an object at a given 
distance the same amount of accommodation 
and convergence will be required. For in- 
stance, to view an object at 13 inches, it will be 
necessary 'to use three dioptrics of accommo- 
dation and three meter angles of convergence, 
and if the object was brought nearer, the accom- 
modation and convergence would increase an 
equal amount. The same nerve (third or motor 
oculi) supplies the muscles that perform both 
functions. Turning the eyes outward from their 


position of rest is called negative convergence, 
or abduction; turning the eyes inward from 
their position of rest is called positive converg- 
ence, or adduction. The number of degrees of 
convergence that can be used without changing 
the accommodation is called relative converg- 
ence. The total amount one has, the Amplitude. 
Converge. Directed toward the same point. 

Convex. That which has a rounded and elevated 
surface. The surface, if continued at the same 
radius of curvature, would form a complete 
circle, or sphere. 

Convexo-concave. Convex on one side and con- 
cave on the other. If the convexity exceeds the 
concavity it is known as a periscopic convex 
lens. If the concavity exceeds the convexity it 
is known as a periscopic concave lens. 

Copiopia (kop-i-o'-pi-ah). (Gr. kopos = fatigue + 
ops = eye.) A worn-out state of the eye, caused 
by eye-strain. 

Coquille-Plano Lenses (plus 8D. on one side and 
minus 8D. on the other). MiCoquille are plus 
4D. on one side and minus 4D. on the other. 
They are nearly always colored. 

Cored Isis (kor-ek'-lis-is). (Gr. kore = pupil + 
kleisis = closure.) That condition in which the 
pupil of the eye is obliterated. 

Corectasis (kor-ek'-tas-is). Dilatation of the pupil. 

Corectome (kor-ec'-to-me). An instrument used in 
cutting for iridectomy. 

Corectomy (ko-rek'-to-me). (Gr. kore = pupil -f 
ektome = excision.) See Iridectomy. 

Tiorectopia (kor-ec-to'-pi-ah). (Gr. kore = pupil + 


ektopos = out of place.) That condition in 
which the pupil is displaced. 

Coredialysis (kor-e-di-al'-ys-is). An operation in 
which the iris is detached from the ciliary liga- 
ment for a new pupil. 

Corelysis (ko-rel'-is-is). (Gr. kore = pupil + lysis 
= a loosening.) The loosening of adhesions be- 
tween the capsule of the lens and the iris. 

Coremorphosis fkor-e-mor'-pho-sis). (Gr. kore =^ 
pupil -f morphosis = formation.) Creation of an 
artificial pupil. 

Coreometer (kor-e-om'-et-er). (Gr. kore = pupil + 
metron = measure.) A contrivance used for 
measuring the pupil. 

Co re plasty (Gr. kore = pupil + plasso = I form). 
An operation for forming an artificial pupil. 

Cornea (kor'-ne-ah). (L. corneus = horn-like.) 
The anterior one-sixth of the first tunic of the 
eyeball. It is transparent, convex, and fitted 
into the sclerotic like a watch crystal, having a 
radius of 7.8 mm. on its anterior surface and 6.5 
mm. on the posterior surface. It has a vertical 
diameter of about 11 mm. and the horizontal 
diameter is 12 mm. In thickness it is about 1 
mm. at the center, while at the periphery it is 
1.12 mm. The cornea has no blood-vessels ex- 
cept for a narrow space about 1 mm. wide at 
the margin, derived from the anterior ciliary 
arteries. The venous roots become tributaries 
of the anterior ciliary vein. The cornea is well 
supplied with nerves and lymphatics. It serves to 
transmit light into the eye, and next to the layer 
of tears becomes the first refracting medium. It 
is convex in front and concave behind. Its curv- 


atiire varies in different individuals. It is com- 
posed of five layers, arranged as follows, from 
without inward, namely: (1) Conjunctiva epi- 
thelium; (2) Bowman's membrane; (3) Cornea 
proper; (4) Membrane Descemet; (5) Endothe- 
lium. The first layer (conjunctiva epithelium) 
serves to protect the nerves in Bowman's mem- 
brane from cold, wind, and dust, and at the 
same time gives a highly polished surface to the 
cornea. The second layer (Bowman's mem- 
brane) is a layer of sensitive nerves and elastic 
tissue, and protects the cornea proper on the 
anterior side, and at the same time gives the 
cornea an elastic nature. The third layer (cor- 
nea proper) is the foundation layer of the cor- 
nea. It is composed of a horn-like substance 
and is non-sensitive and merely serves to keep 
the cornea in shape. The fourth layer (Mem- 
brane Descemet) is a layer similar to Bowman's 
membrane, and protects the cornea proper from 
any diseased condition from the posterior side. 
The fifth layer (endothelium) is a lining mem- 
brane which separates the aqueous humor from 
the fourth layer, and at the same time forms a 
sort of sac which contains the aqueous humor. 
The cornea has an index of refraction of 1.33. 
Its nerve supply arises from the ciliary nerves. 

Cor'neal. Pertaining to the cornea. 

Corneal Astigmatism. See Astigmatism. 

Corneal Facets (fas'-ets). Small, plain, distinct 
surfaces of the cornea. 

Corneitis (cor-ne-i'-tis). inflammation of the cor- 

Corneo-iritis. Inflammation of the iris and cornea. 

Corneosciera. The cornea and sclera taken to- 
gether, forming the external coaling of the 

Corradiation (kor-ra'-di-a'-shun). A conjunction or 
concentration of rays in one point. 

Correction. Making good an abnormal condition, 
such as correcting an error of refraction. 

Cortical (kor'-tik-al). (L. cortex = bark.) To be 
near the border. Cortical Cataract is that vari- 
ety in which the opacity begins at the border of 
the crystalline lens and gradually spreads 
toward the center, which it sooner or later 

Cosecant (ko-se'-kant). The secant of the comple- 
ment of an arc or angle. 

Cosine (ko'-sin). The sine of the complement of 
an arc or angle. 

Cotangent (ko-tan'-jent). The tangent of the com- 
plement of an arc or angle. 

Couching. That condition in which the lens is 
displaced in cataract. This operation is now 

Coversed Sine (ko-versf sine). The versed sine 
of the complement of an arc or angle. 

Cover Test. A test for muscular imbalance by 
covering one eye and observing its movement 
while uncovering, the point of fixation being 

Cramp. A spasmodic muscular contraction. 

Cribriform (krib'-ri-form). (L. cribrum = sieve -h 
forma = form.) Perforated like a sieve. 

Critical Angle (krit'-ik-al). The least angle of in- 
cidence at which a ray of light traveling in a 


denser medium is totally reflected at the sur- 
face which separates it from a rarer medium; 
also known as limit angle. The limit angle of 
crown glass is 40° 49'; that of flint glass, 37° 36'. 

Crossed Diplopia. See Diplopia. 

Crystalline (Gr. "crystal"). Clear, transparent. 
Resembling or of the nature 'of crystal. 

Crystalline Lens (krys'-tal-lin). The lens of the 
eye, which resembles a crystal. It is a bi- 
convexed, transparent, elastic body having a 
diameter of about 8.5 mm. and its axial thick- 
ness about 3.6 mm. It has a radius of curvature 
on the anterior surface of 10 mm., and that of 
the posterior surface 6 mm,, while the eye is in 
a state of rest. It is located in the hyaloid fossa 
of the vitreous, just behind the pupil, and is 
made up of layers like an onion, which gives it 
an elastic nature. The lens itself is enclosed in 
the lens capsule, which is held in position by 
the suspensory ligaments. Its index of refrac- 
tion is 1.43, and it represents from 16 to 19 diop- 
tries of plus when the eye is at rest. 

Crytometer. See Curtometer. 

Cube (kub). (Gr. kubos =^ a die, a cube.) (a) A 
regular solid with Kix square faces; (b) to raise 
to the third power; (c) the third power of a 

Cube Root. The cube root of a perfect third power 
is one of the three equal factors of that power. 
A number which has not a perfect third power 
has not three equal factors. 

Cuneus (cu'-ne-us). (L. wedge.) The wedge-shaped 
portion of the occipital lobe of the cerebrum, 
situated between the occipital and calcarine 


fissures. The cuneus receives the cortical ter- 
mini of the optic tract. 

Cupped Disc. That condition in which the optic 
disc has become cupped, as seen in glaucoma. 

Curtom'eter. An instrument for measuring curved 

Curvature (curv'-a-ture). The bending of a line 
without forming angles. 

Cutaneous (ku-ta'-ne-us). Pertaining to the skin. 

Cyclitis (cyc-li'-tis). (Gr. kyklos = circle -f itis = 
inflammation.) Inflammation of the ciliary 

Cyclochoroiditis (si-klo-ko-roid-i'-tis). Inflamma- 
tion of the choroid e.nd ciliary body. 

Cycloid (si-kloyd). Like a circle. 

Cyclophoria (cyc-lo-fo'-ri-ah). (Gr. kyklos == circle 


+ phora = movement.) That condition in which 
the vertical axis of the eye inclines to the right 
or left instead of standing vertically, the extrin- 
sic muscles being at rest. 

Cyclopia (si-klo'-pe-ah). (Gr. kyklos = circle -f 
ops = eye.) A single eye in center of forehead. 

Cycloplegia (cy-clo-ple'-gi-ah). (Gr. kyklos = cir- 
cle + plege = stroke.) Paralysis of the ciliary 

Cycloplegic. A drug which produces paralysis of 
the ciliary muscles or muscles of accommoda- 

Cyclot'omy (Gr. kyklos = circle + tome = inci- 
sion). Operation of cutting the ciliary body of 
the eye. 

Cyclotropia (Gr. kyklos = circle -f trope = turn). 
The actual turning of an eye on its optic axis. 

Cylinder (cyl'-in-der). (Gr. kylindros = a roll.) 
See Lens. 

Cylindrical. Relating to or the shape of a cylinder. 

Cyst (sist). (Gr. kystis = bladder.) Any sac con- 
taining a liquid. Dermoid cyst is congenital. 
It is a painless, uninflammed spheroidal mass, 
situated generally at the outer angle of the 
orbit, on a level with the outer end of the eye- 
. brow. 

Cystitome (sis'-tit-om). An instrument used for 
opening the sac of the crystalline lens. 

Cystot'omy (Gr. kystis = bladder -f tome = inci- 
sion). Incision of the capsule of the Crystalline 



• Abbreviation for dioptry, dexter, or dose. 
Dacryadenalgia (dak-ry-ad-en-ar-gi-ah). (Gr. dak- 
ryon = tear + aden = gland + algos = pain.) 
Pain in a lacrimal gland. 

Dacryagogue (dak'-ry-ag-og). (Gr. dakryon = tear 
+ agogos = leader.) A medicine which causes 
a flow of tears. 

Dacryoadenitis (dak-ry-o-ad-en-i'-tis). (Gr. dak- 
ryon = tear + aden = gland + itis.) Inflamma- 
tion of a lacrimal gland. 

Dacryocele (dak'-ry-o-cele). (Gr. dakryon == tear 
+ kele = hernia.) A protrusion of the lacrimal 

Dacryocyst (dak'-ry-o-cyst). (Gr. dakryon = tear 
-f- kystis = sac.) The tear sac. 

Dacryocystalgia (dak-ry-o-cyst-al'-gi-ah). (Gr. dak- 
ryon = tear + kystis ^ sac -f- algos = pain.) 
Pain in the lacrimal sac. 

Dacryocystitis (dak-ry-o-cys-ti'-tis). Inflammation 
of the lacrimal sac. 

Dac'ryoid. Resembling a tear. 

Dacryoma (dak-ry-o'-ma). (Gr. dakryon ^ tear, 
and suffix oma, "morbid state.") A lacrimal 
tumor which causes an obstruction of the lac- 
rimal puncta, so that the tears flow over the 
lids upon the cheek. 

Dacryon (Gr. "a tear"). 

Dacryops (dak'-re-ops). (Gr. dakryon = tear -f 
ops = eye.) A watery eye. Applied to a swell- 
ing of the lacrimal sac or one of its ducts. 

Dacryorrhea (Gr. dakryon = tear + rhoia = flow). 
Excessive or morbid flow of tears. 


Dacryopyorrhea (Gr. dakryon = tear + pyon = 

pus + rhoia = flow). Discharge of pus from the 

lacrimal duct. 
Dacryopyo'sis (Gr. dakryon = tear + pyosis = 

suppuration). A discharge of tears mixed with 

purulent matter. 

Daltonism (dawl'-ton-izm). Color-blindness. 

Day-blindness (day-blind'-ness). Partially blind by 
day, with better vision at night. See Hemera- 

Decameter (dek'-a-me-ter). Ten meters. 

Decentered (de-cen'-terd) Lens. A lens with its 
optical center to one side or above or below the 

Decentered Lenses. 

Decentering of Lenses. Instead of having a prism 
and a lens combined, where you wish to obtain 
the effect of both, it is possible to get the same 
result by simply decentering the optical center 
of the lens. The optical center of a plus lens 
is at the thickest part, and in the minus at its 
thinnest part, while the geometrical center of a 
lens is the point midway between all edges. A 
1-dioptry lens decentered 10 mm. will give the 
effect of a 1° prism, while a 2-D. lens will only 
require to be decentered half this amount, or 
5 mm. ; a 3-D. lens, one-third of this amount, for 
the same effect, and so on according to the 
strength of the lens. To obtain the effect of a 

2° prism these lenses must be decentered twice 
as much — that is to say, a 1-D. lens, 20 mm.; a 
2-D. lens, 10 mm.; a 3-D., 6.3 mm. From this 
table one can easily figure the exact amount 
any lens should be decentered to obtain a given 
prismatic effect. Law of Decentration: Any 
lens is capable of producing as many prism 
dioptrics as the lens possesses dioptrics of re 
fraction, provided it is decentered 1 cm. — Pren- 
tice, Archives of Ophthalmology, Vol. XIX, No. ] 
and No. 2, New York, 1890. 

Decentration (de-cen-tra'-tion). The act of re- 
moving from a center. 

Decimal (desM-mal). (L. decern = ten.) Pertain- 
ing to ten. 

Decimeter (des'-i-me-ter). One-tenth of a meter. 

Decomposition of Light. If parallel rays of sun- 
light pass through a prism it is not only re- 
fracted but it is also decomposed into its vari- 
ous colors. This is due to the unequal refrangi- 
bility of the different colored rays which form 
white light, the violet being refracted the most 
and the red the least, thus forming the spec- 

Decussation (de-ku-sa'-shon). (L. decussare = to 
cross.) The act of crossing or intersecting; the 
crossing of two lines, rays, fibers of nerves, etc. 
Through the decussation of the rays in the 
pupil of the eye the image of the object on the 
retina is inverted. 

Defect (de-fecf). A departure from the normal. 
When speaking of defects of vision we mean 
the visual power of the eye is not normal. 


Defining Power, Definition. The power of a lens 
to give a clear outline. 

Denominator (de-nom'-i-na-tor). (L. denominare = 
to name.) (Arith.) That number placed below 
the line in fractions which shows into how many- 
parts the unit is divided. (Alg.) That part of 
any expression under a fractional form which is 
situated below the horizontal line signifying 

Deor'sumvergens (L. deorsum = downward + ver- 
gere = to incline). Dowmward turning of the 

Depilation (dep-il-a'-shun). (L. de ^= from -|- pilus 
= hair.) The removal or loss of the hair. 

Deplumation (de-plu-ma'-shun). (L. de = from + 
pluma = feather.) Loss of eyelashes by disease. 

Deprimens Oculi (dep'-ri-mens ok'-u-li). (L. depri- 
mere = to depress.) The rectus inferior muscle. 

Descemet's iVIembrane (des-ce-mets' mem'-brane). 
The fourth layer of the cornea. See Cornea. 

Descemetitis (des-em-e-ti'-tis). Inflammation of 
Descemet's Membrane. 

Deviation (de-vi-a'-shun). (L. de = from + via = 
way.) Turning aside, as in strabismus. Conju- 
gate d., deviation of both eyes to the same side. 
IVIinimum d., the smallest deviation of a ray 
that a given prism can produce. 

Dexter, Dextra (dex'-ter, dex'-tra). On right side. 

Dextrad (dex'-trad). (L. dexter = right.) Toward 
the right side. 

Dextrophoria (deks'-tro-phor'-ia). (L. dexter = 
right + Gr. phoria = tending.) That condition 

in which the eyes turn to the right when the 
extrinsic muscles are in a state of rest. 

Diacaustic (di'-a-kas'-tik). A curve formed by the 
consecutive intersections of rays of light re- 
fracted through a lens, and when reflected it is 
called catacaustic. 

Diagonal (di-ag'-o-nal). (Gr. dia = through + 
gonia = comer, angle.) A line through the an- 
gles of a figure, but not lying in its sides or 

Diameter (Gr. diametros; dia = through + metron 
= measure). A straight line joining opposite 
points of a circle, drawn through the center. 

Diaphaneity (di-af-a-ne'-i-ty). Transparency; the 
power of transmitting light. 

Diaphanous (di-af'-a-nous). Having power to trans- 
mit rays of light, as glass. 

Diaphragm (di'-a-fram). (Gr. diaphragma = a 
partition wall.) A term applied to the partition 
with a central aperture in optical instruments 
so that rays of light may be controlled. The iris 
with its pupil constitutes the diaphragm of the 

Diapyesis (di-ap-i-e'-sis). Suppuration. 

Diffraction (dif-frak'-shun). (L. diffractus; diffrin- 
gere = to break up.) Deflection or decomposi- 
tion of light in passing by the edges of opaque 
bodies or through small apertures. 

Diffusion (dif-fu'-shun). n. (Optics) A spreading or 
scattering of rays of light, causing a blurred 
image by imperfect refraction. 

Digit (dij'-it). (L. digitus = finger.) The number 
represented by any one of the ten symbols 0, 1, 


2, 9. The term is more often used to desig- 
nate one of the ten sj^mbols mentioned. 

Dilatant. A medicine that causes dilatation. 
Dilatation (di-la-ta'-shun). (L. dilatare = to ex- 
pand.) The expansion of any orifice or canal. 

Dilator (di-la'-tor). Dilator iris refers to the radiat- 
ing fiber of the iris which dilates the pupil. 

Diopter (di-op'-ter). (Gr. dia = through + opsomai 
= I shall see.) A leveling instrument of ancient 
times, equipped with sights at both ends and a 
water level in its center. The theodolite, by 
Hipparchus, the ancient Greek mathematician. 

Dioptometer (di-op-tom'-e-ter). An instrument for 
testing ocular refraction. 

Dioptometry (di-op-tom'-e-tre). The measurement 
of ocular accommodation and refraction. 

Dioptral, a. Applied to the refractive power of 
ophthalmic lenses numbered according to the 
metric system, and in which the unit of power 
has a focal length of 1 meter. Thus, a 1-dioptry 
lens is specifically a member of the dioptral 
system, whereas a 40-inch telescope lens is a 
member of a dioptric system. 

Dioptric (di-op'-tric). See Dioptry, 

Dioptrical (di-op'-tri-kal). Of or pertaining to 

Dioptrics (di-op'-trics). That branch of optics 
which treats of the refraction of light by any 
transparent media, as air, water, or glass. 

Dioptron (di-op'-tron). (Surg.) A dilating specu- 

Dioptry, n. (di-op'-tri). (Gr. dia = through + opso- 
mai = I shall see.) The unit for expressing the 


refractive power of a lens. The refractive power 
of a lens which will focus parallel rays of light 
at a distance of 1 meter. A lens of 2 dioptries 
f 2 D.) has a focal length of i meter. Synonyms: 
Dioptre, Dioptric. See Focus. 

Diplocoria (dip-lo-ko'-re-ah). (Gr. diplous = dou- 
ble -j- kore = pupil.) Double pupil. 

Diplopia (dip-lo'-pe-ah). (Gr. diplous = double -|- 
opsis = vision.) Double vision; seeing one ob- 
ject as two. The object of convergence is to 
direct the yellow spot (or macula lutea) in each 
eye toward the same point, so as to obtain 
single vision; diplopia, or double vision, at once 
resulting when the image of an object falls on 
parts of the retina which do not exactly corre- 
spond in the two eyes. 

Binocular d., double vision only when the two 
eyes are exposed to view. Heteronymous d., 
where the object seen with the right eye ap- 
pears on the left side, and that of the left eye 
on the right side. Homonymous d., where the 
object of the right eye appears on the right side 
and the object of the left eye on the left side. 
Monocular d., diplopia with a single eye. 

DIplopiometer (dip-lo-pi-om'-e-ter). An instrument 
for measuring diplopia. 

Disc (disk). A round body which resembles a 
small circular plate. Optic d., a whitish circular 
spot in the retina representing the entrance of 
the optic nerve into the globe of the eye. 

Discission (dis-ish'-un). (L. discindere = to split.) 
The rupture of the capsule of the crystalline 
lens in the operation for soft cataract. 

Diseases of the Eye. The diseases of the eye are 


many, but nearly all of them can be directly or 
indirectly attributed to eye-strain or impurity 
of the blood. First, relieve any eye-strain by 
glasses; second, keep the bowels regular; third, 
fresh air and exercise. When the patient re- 
quires further attention, proper treatment 
should be instituted. 

Disparate Points (dis'-par-at). (L. disparare = to 
separate.) Points on the two retinae upon which 
light does not produce the same impression. 

Disperse (L. dispersus; dispergere = to scatter 

Dispersing Lens (dis-per'-sing). Same as concave 

Dispersion (dis-per'-shun). The process of scatter- 
ing the rays of light through any kind of a lens. 

Distichiasis, Distichia (dis-te-ki'-a-sis, dis-tik'-e-ah). 
(Gr. di = double + stichos = row.) That condi- 
tion of the eyelashes in which a second row 
rubs against the cornea, causing inflammation. 

Divergence (di-ver'-gens). (L. di = apart -f ver- 
gere = to incline.) To turn outward from 

Dividend (div'-i-dend). (L. dividere = to divide.) 
A number or quantity to be divided by another 
is called the dividend. 

Donders (Frans Cornelis). A Dutch physician, 
born at Tilburg, Holland, May 27, 1818. He was 
educated at Utrecht, where he became a pro- 
fessor of physiology. 

Double Prism. An opaque disc found in test-case 
with a slit-like opening. Over this slit there 
are two prisms with their bases together. Used 
for testing for muscular imbalance. To test for 
muscular imbalance use a small round bright 


frosted light (about % to i/4 inch, at 20 feet), 
the double prism will make this light appear as 
two, both of which will be displaced from their 
true position. Over the other eye place the red 
glass disc which will color the light red. The 
patient will then see three lights, two white, 
one red. If the red light is seen midway be- 
tween the two white, no muscular imbalance is 
present; if not, the prism that will bring it 
there is the measure of deviation. The two 
prisms used in this disc are of five diopters 
each, joined base to base. When the line formed 
by the bases is placed horizontally before the 
pupil of an eye the light will be seen as two, 
separated vertically from their true position 
leaving the other eye, which is wearing the red 
glass disc, to see the light in its true position. 

Double Vision. Seeing one object as two. See 

Doublet (doub'-let). Composed of two lenses. 

Duct (dukt). A tube for conveying a fluid. 

Dura Mater. The outermost membrane of the 
brain, spinal cord, optic nerve, and capsule of 

Dural Sheath. The external covering of the optic 

Dynameter (dy-nam'-e-ter). An instrument for de- 
termining the magnifying power of telescopes. 

Dynamic (Gr. dynamis = power). The powers 
whereby bodies are put in motion. 

Dynamic Refraction (dy-nam'-ic). (Gr. dynamis = 
power.) The refraction of the eye (dioptric 
power) while using all of its accommodation 
and adjusted for the near point of vision. The 


difference between the dynamic and static re- 
fraction is known as the Amplitude of Accom- 

Dynamic Skiametry fdi-nam'-lc sky-am'-e-try). 
(Gr. dynamis = power -f skia = shadow -)- met- 
ron = measure.) Is defined as the measuring of 
the refraction of an eye by the shadow test 
(retinoscopy) while the accommodation is under 
tension. It is the opposite of static skiametry, 
where the accommodation is relaxed. 

The value of dynamic skiametry is said to be 
in its offering a mechanical means for absorb- 
ing spasms of accommodation, and thus reveal- 
ing latent errors v/ithout recourse to cyclopleg- 
ics. In the practice of the dynamic method the 
patient is required to accurately fix his vision 
on a test card that is situated the same distance 
away (say, 16 inches) that the nodal point of 
an examiner's eye (behind the peephole of his 
skiascope) is situated during the examination; 
that is, the fixation and observation must be 
exactly the same. Under these conditions, if 
the examiner will keep adding all the plus 
spherical lens power possible before reversal of 
the shadow takes place (even though the 
shadow does not indicate hyperopia) it will be 
found that an eye will surrender that portion 
of its accommodation which is in excess of what 
is needed to correctly harmonize with the con- 
vergence required for the distance at which the 
examination is made. With the dynamic method 
no allowance in strength of lens is made for the 
working distance, as by the static method, and 
where the patient is presbyopic or has latent 

hyperopia there will be a difference in the find- 
ings between the dynamic and static. 

The recognized text-book on the subject is 
called "Dynamic Skiametry in Theory and Prac- 
tice," by Andrew Jay Cross, D.O.S., of Columbia 
University, New York City, who is the origi- 
nator of the method. 
Dynamometer (dy-na-mom'-e-ter). An instrument 
for measuring force or power; especially the 
muscular power. 

Dynamometry (dy'-na-mom'-e-try). The process of 

measuring force while doing work. 
Dyslexia (dis-lex'-se-ah). (Gr. dys = bad + lexis 

= word.) Inability to read caused by a disease 

of the brain. Vision is good, but the power to 

read is wanting. 

Dysopsy (dys-op'-sy). (Gr. dys = faulty -f- opsis = 
vision.) Dimness of vision. 

Hi CCENTRIC (ek-sen'-trik). (Gr. ek = out + 
kentron = center.) Away from a center. 

Ecchymosis (Gr. ek = out -f chymos = juice). An 
extravasation of blood into tissue. 

Ectasia (ek-ta'-se-ah). Abnormal distention or 
dilatation of a part. 

Ectiris Cek-ti'-ris). (Gr. ektos = outside + iris.) 
The external portion of the iris. 

Ectochoroidea (ek-to-cho-roi'-de-ah). (Gr. ektos = 
outside.) The outer layer of the choroid coat. 

Ectocornea (ek-to-kor'-ne-ah). Outer layer of the 


Ectoretina (ek-to-ret'-in-ah). (Gr. ektos = out- 
side.) Outermost layer of the retina. 

Ectropion (ek-tro'-pi-on) Ectropium (Gr. ek = out 
+ trope =^ a turning). Turning out or inside 
out of the edge of an eyelid. 

Edema (e-de'-mah). (Gr. oidema = a swelling.) 
An accumulation of serum in the cellular tissue. 

Efferent (ef'-er-ent). (L. effere = to bring out.) 
Conveying outward, as from center to periph- 
ery; applied to motor nerves and vessels con- 
veying from the center. The opposite of afferent. 

Embolism (Gr. embolisma = a patch). Obstruc- 
tion of a vessel by an embolus. 

Em 'bolus. A clot or plug which obstructs a blood- 

Emergent ("to come out of"). A ray of light after 
having passed through a refracting medium. 

Emissive. Radiating. 

Emmetropia (em-met-ro'-pi-ah). (Gr. emmetros = 
in measure -^ ops = eye.) That condition in 

An emmetropic eye receiving one set of parallel rays. 
It must be remembered that the three rays representing 
the set come from one point, but the point is so far away 
that the rays appear to be parallel because the divergence 
is so slight. 

which all parallel rays of light after entering 
the eye are brought to a focus on its retina, 

ijrL<>>io IT Kjy^r\.i:^ ± 

while th^ muscles of accommodation are in a 
state of rest. 

Emmetropia has no reference whatever to 
sight, or disease, but simply means that the 
optical apparatus has the correct focal length 
for the globe of the eye. In other words, no lens 
is required for distant vision. When this condi- 
tion does not exist the eye is out of measure, or 

Emphyse'ma (Gr. en = in + physema = a blow- 
ing). The infiltration of air into the cellular 
tissues of the orbit. May be caused by rupture 
of the lachrymal sac. 

Encan'this (Gr. en = in + kanthos = canthus). A 
minute tumor in the inner canthus of the eye. 

Endothelium (Gr. endon = within + thele = nip- 
ple). A layer of flat cells lining serous cavities, 
blood-vessels, and lymphatics. The fifth layer 
of the cornea. 

Energy. (Physics) Capacity for performing work. 

Enervate (en-er-vate). To deprive of nerve, force, 
or strength; to render feeble. 

Enophthalmus (en-of-thal'-mus). (Gr. en = in -f 
ophthalmos = eye.) A condition where the eyes 
are deep-seated. 

Enstrophe (en*-stro-fe). (Gr. en = in -f strophe = 
a turning). A turning inward. 

En'tad (Gr. entos = within). Toward a center. 

Entochoroidea (en-to-cho-roi'-de-ah). (Gr. entos = 
within 4- chorioeides = choroid). The inner layer 
of the choroid. 

Entocornea (en-to-cor'-ne-ah). (Gr. entos = with- 
in.) Descemet's membrane. 


Entoptic (en-top'-tic). (Gr. entos = within -f op- 
tikos ^ visual.) Situated within the eye. 

Entoptic Phenomenon (en-top'-tic phe-nom'-e-non). 
That which is peculiar with itself, such as 
Muscae Volitantes. 

Entoptoscopy (en-top-tos'-co-py). (Gr. entos = 
within + optos == visible + skopeo = I view.) 
Inspection of the interior of the eye. 

Entoretina (en-to-ret'-in-ah). The nervous or inner 
layer of the retina. 

Entropion (Gr. en = im + trope = a turning). See 

Entropium ( en-tro'-pi-um). A turning in or inver- 
sion of the eyelid or eyelashes. 

Enucleate (e-nu'-cle-ate). (L. e = from -f- nucleus 
= kernel.) To remove from its cover. 

Enucleation fe-nu'-cle-a'-shun). Operation for the 
removal of the eye. 

Ephidro'sis. (Gr. "I sweat.") An excessive se- 
cretion of the sweat glands of the eyelids. It 
causes itching, irritation, and inflammation of 
the skin and conjunctiva. It is difficult to cure. 

Epicanthus (ep-i-can'-thus). (Gr. epi = upon -|- 
kanthos = canthus.) A fold of skin projected 
over the inner canthus. 

Epiphora (e-pif'-or-a). (Gr. epi = upon + phoria 
= tending.) An overflow of tears, causing them 
to run down the cheek. 

Episclera (Gr. epi ^ upon + skleros = hard). The 
connective tissue between the sclera and the 

Episcleral (ep-i-scle'-ral). Situated over the sclera 
of the eye. 


Episcleritis (ep-i-scle-ri'-tis). Inflammation of the 
outer layers of the sclera. 

Epithello'ma. Cancer composed largely of epithe- 
lial cells, and is the most frequent of malignant 
growths affecting the eyelid. It seldom appears 
before the age of forty. 

Epithelium (ep-i-the'-le-um). (Gr. epi = upon + 
thele = nipple.) The non-vascular, external 
layer of the skin and mucous membrane. First 
layer of the cornea. 

Equal (e'-kwal). (L. aequalis = equal.) Having 
the same value. 

Equation (e-kwa'-shun). A proposition asserting 
the equality of two quantities and expressed by 
the sign " = " between them. In Algebra, an 
equality which exists only for particular values 
of certain letters called unknown quantities. 

Equilateral (e-kwi-lat'-e-ral). (L. aequus = equal 
-f latus = side.) Having all of the sides equal. 

Equil'ibrating Operation. Tenotomy of the muscle, 
which antagonizes a paralyzed muscle of the 

Errors of Refraction. Abnormal conditions of re- 
fraction in the eye. 

Erythropsia (erythro'-psia). (Gr. erythros = red -f 
opsis = vision.) Red vision; a condition in 
which all objects appear to be tinged with red. 

Eserine (es'-er-een). An alkaloid obtained from 
the calabar-bean, which will cause contraction 
of the pupil. It has an action exactly opposite to 
that of atropine, since it places the iris and 
ciliary muscle in a state of tonic contraction. 
Consequently, miosis develops, so that the pupil 
is about the size of a pin's head, with adjust- 


merit of the eye for the near point, as if 
marked myopia were present. We generally 
apply sulphate of eserine in 1 per cent solution. 
This solution, when freshly prepared, is color- 
less, but after some days becomes red, although 
without losing its activity. The instillation of 
eserine produces, simultaneously with the 
changes in the iris, a feeling of great tension 
in the eye, and frequently headache, and even 
nausea, so that with many persons it cannot be 
employed. For this reason, hydrochloride of 
pilocarpine, prescribed in a 1 to 2 per cent solu- 
tion, is recommended as a miotic for ordinary 
use. Its solution keeps better than that of 
eserine, and does not act as powerfully as the 
latter, but is not accompanied by any unpleas- 
ant complication. Eserine is best reserved for 
those cases in which pilocarpine is ineffectual. 

Esophoria (es-o-fo'-ri-ah). (Gr. eso = inward + 
phoria = a tending.) That condition of the eyes 
in which the visual axes, although parallel when 
in use for distant vision, deviate inward when 
the extrinsic muscles are in a state of rest. 

Esotropia (e-so-tro'-pi-ah). (Gr. eso = inward + 
trope = turn.) This term expresses a stronger 
meaning than Esophoria, in which there is 
merely a tendency, while in Esotropia there is 
a positive and visible appearance of the eyes 
turning inward. 

Evolution (ev-o-lu'-shun). (L. evolvere == to un- 
roll.) The extraction of roots from powers. 

Excavation (ex-cav-a'-shun). (L. excavare — to 
hollow out.) Excavation of optic nerve; cupping 
or hollowing of the optic disc. 


Exophoria (ex-o-fo'-ri-ah). (Gr. exo = outward + 
pliora ^^ a tending.) That condition of the eyes 
in which the visual axes, although parallel when 
in use for distant vision, deviate outward when 
the extrinsic muscles are in a state of rest. 
The internal rectus muscles are overworked 
from this continual convergence and relieved 
only when the lids are closed, or prisms worn, 
base in, that are strong enough to bend the light 
to suit the eyes in their deviating position of 

Excphthalmic Goiter (eks-off-thal'-mik goi'-ter). A 
goiter with exophthalmos and cardiac palpita- 
tion; Basedow's disease; Graves' disease. The 
most prominent symptoms are protrusion of the 
eye, excited action of the heart, enlarged thy- 
roid (goiter), and certain nervous phenomena. 
The protrusion is almost invariably bilateral, 
though not infrequently greater on the right 
side. The upper lids do not follow the eyeball 
in looking down (Von Graefe's sign) ; infre- 
quency of involuntary winking (Stellwag's sign) 
and abnormal width of the palpebral aperture 
are also found. 

Exophthalmos (ex-of-thal'-mos). (Gr. ex = out + 
ophthalmos = eye.) Abnormal protrusion of the 

Exor'bitism (Jj. ex = out + orbita =^ orbit). Pro- 
trusion of the eyeball. 

Exotropia (ex-o-tro'-pi-ah). (Gr. exo = outward + 
trope = turn.) When the eye is turned outward 
from parallelism. See Divergent Strabismus. 

Extraction (ex-trak'-shun). (L. extrahere = tu 



draw out.) The removal of a body by surgical 

Extravasation (eks-trah-vas-a'-shun). (L. extra = 
out of -f vas = vessel.) The escape of fluids 
from their proper vessels, into surrounding- 

Extremes (eks-tremz'). (L. extremus = outer- 
most.) The first and last terms of a proportion 
or of any other related series of terms. 

Extrin'sic. Of exterior origin. E. Muscles are 
those on the outside of the organ. 

Eye (L. oculus = eye). The organ of sight. The 
function of each eye, taken singly, is to form 
upon the retina, or nervous membrane which 


lines the inside and back part of the organ, a 
sharply defined inverted image of any object 
looked at. The eye resembles a photographer's 
camera inasmuch as the image produced upon 
the retina is precisely the same as that pro- 
duced on the ground glass of a camera. By 
means of the optic nerve the image that is re- 
ceived on the retina is conveyed to the brain, 
which recognizes the visual appearances and 
completes the act of seeing. More than this we 
do not know, but we do know that it depends 
upon the sharpness and clearness of the retinal 
image. If the image is blurred and indistinct it 
will be impossible for the brain to recognize the 
object accurately. 

Eyebrows. They are two projecting arches of in- 
tegument covered with short, thick hairs, which 
form the upper boundaries of the orbits. 

Eye Ground. The inside and back part of the eye. 
The Fundus. 

Eyelashes. The hair of the eyelids. 

Eyelids. The anterior covering of the eye; that 
portion of movable skin with which the eyeball 
is cpvered or uncovered at will, protecting it 
from injury by their closure. The upper lid is 
the larger, the more movable of the two, and is 
supplied by a separate muscle, levator palpeb- 
rae superioris. When the eyelids are open an 
elliptical space is left between their margins,' 
the extremities of which correspond to the 
junction of the upper and lower lids, and are 
called canthi. The outer canthus is more acute 
than the inner, and the lids here lie in close 
contact with the globe, but the inner canthus is 
prolonged for a short distance inward, toward 



the nose, and the two lids are separated by a 
triangular space, the lacus lachrymalis. At the 
commencement of the lacus lachrymalis and on 
the margin of each eyelid is a small conical 
elevation, the lachrymal papilla (the puncta), 
the apex of which is pierced by a small orifice, 
the commencement of the lachrymal canal. 
Structures of the Eyelids: The eyelids are com- 
posed of the following structures, taken in their 
order from without inward: Integument, areolar 
tissue, fibers of the orbicularis muscle, tarsal 
cartilage, fibrous membrane, meibomian glands, 
and conjunctiva. The upper lid has, in addition, 
the aponeurosis of the levator palpebrae. The 
integument is extremely thin, and continuous 


1. Orbioularis Palpebrarum Muscle. 

'2. Opening between the lids (Palpebral Fissure.) 

3. Lachrymal Glands, where the tears have their 

4. Its ducts opening in the fold of the Conjunctiva. 
r>. Conjunctiva lining inside of lid. 

G. Puncta I^acrimalia, through which the tears pass. 
7. Inner Canthus. 

at the innrfriii of tin- lids wiih »h«' coiijuncl v .1. 
The Subcutaneous Areolar Tissue in vrry \h\ 
and delicate, seldom contains any fal, and is 
extr« I ' ' * ' t(t srrouB infiltration. 


WITH THK <«».\Jl .M ii\ A ui MuVKD. 

1. Orl»Jn of \hr Triinor-tariil Mii»< Ir. 

2, Hupcrlor (U>li(jut< Mu*i !•■ ■■»••• VNiolnir •»' •> 


8. Inferior Oblhiur Mu«rl< 

4 Atlachtnonl of <^rblrulnrlH r.iIi>oliri«run» "H > .••.! 

rv. Tariial Carill»c<ii vhowing position of MvlboiiflMtt 

n Opening l>«iwv«n ih» lids known mm xh* Palp^lM . '. 

7. i^wer part of Orblrularln Palpebrarum Mop<I<. 

H The Inarrilon of the Trnaor-taral Jkluiirlr nrar i».' 

9. I^rhrymal Sac In th« no**. 

Eyepiece. Th«' lens or combination of lenses m( 
thr !•>»• «'n(l of a tfloHcopi- or othrr optical In- 
Hlrtiment. through whirh th«' imaRe form«»d by 
the object glass is viewed. 

Eyesight. Tho sense of seeing: sl^tht of the oyo; 
vifwinu; obHorvation. 


Jr ACTOR (fak'-tor). (L. facere -- to do.) One of 
two or more numbers which when multiplied 
together produce a given number. 

Facultative (fak'-ul-ta-tiv). (L. facultas = faculty.) 
The power or ability to maintain extra effort 
whenever called upon. 

Falling Eyelashes. (See Milphae and Madarosis.) 
False Image. The image seen wath the deviating 

False Myopia. Due to a spasm of accommoda- 
tion, where the crystalline lens is kept con- 
vexed by the spasm and simulates true myopia. 

Far Point. The far point or punctum remotum is 
the most distant point at which an object may 
be seen clearly, with the muscles of accommo- 
dation at rest. Properly speaking, the far point 
is an optical and not a visual point, and is that 
point from which rays of light will focus on 
the retina, the eye being in a state of rest. 

Fascia (fash'-e-ah). A band or sheet of tissue 
connecting and investing muscles. 

Field of Vision. The area or space which the 

fixed eye can see. 

Filtration Angle. (See Iritic Angle.) 

Fissure (fish'-ur). (L. findo = to split.) In anat- 
omy, a cleft, or slit. Palpebral fissure is the 
opening between the margins of the eyelids. 
Sphenoidal fissure is a large split-like opening 
situated in the upper and back part of the orbit. 
Spheno-maxillary fissure is an opening in the 
back part of the orbit between the sphenoid, 
maxillary and palate and malar bones. Cho- 


roidal fissure is the opening in the choroid 
through which the optic nerve passes to form 
the retina. 

Flap Extraction. Removal of cataract by making 
a flap in the cornea. 

Floating Specks. Small floating opacities in the 
humors of the eye. (See Muscae Volitantes.) 

Focal (fo'-kal). Pertaining to a focus. F. Depth, 
penetrating power of a lens. F. Distance, dis- 
tance between the center of lens and its prin- 
cipal focus. 

Focal Length of Lenses, in inches, centimeters 
and millimeters taken from the basis of forty 
inches as the equivalent to one meter. 

Dioptrics Inches Centimeters Millimeters 

.12 333 833 8333 

25 160 400 4000 

.37 108 270 2703 

.50 80 200 2000 

.62 641/:, 161 1613 

.75 53 133 1333 

.87 46 115 1150 

1.00 40 100 1000 

1.12 36 89 893 

1.25 32 80 800 

1.37 .' 29 73 730 

1.50 27 67 667 

1.62 25 62 617 

1.75 23 .57 571 

1.87 21 54 535 

2.00 20 50 500 

2.25 18 44 444 

2.50 16 40 400 

2.75 15 36 364 


■^ English 

Dioptries Inches Centimeters Millimeters 

3.00 13 33 333 

3.25 12 31 308 

3.50 11 29 286 

3.75 lOVo 27 267 

4.00 10 25 250 

4.50 9 22 222 

5.00 8 20 200 

5.50 7 18 182 

6.00 6il> 17 167 

6.50 6 15 154 

7.00 51/2 14 143 

7.50 514 13 133 

8.00 5 12 VL' 125 

9.00 41/2 11 Ill 

10.00 4 10 100 

11.00 3Vi: 9 91 

12.00 314 8 83 

13.00 3 71/2 77 

14.00 274 7 71 

15.00 2% 6% 662{j 

16.00 21/0 61/4 621;^ 

18.00 214 5Vj 551/2 

20.00 2 5 50 

The above table is approximately correct, yet 
there is a slight difference in close figuring, but 
is correct as far as the optometrist is con- 
cerned; for instance, a + 1-D. lens has a focal 
length of 39.37 inches, while we call it 40. 
Focal Planes. Straight lines through the foci per- 
pendicular to the principal axis. 
Focus (fo'-kus). The point produced by light 
coming to or going from a point. First Princi- 
pal Focus Is at the point the light leaves as 
divergent rays and emerges from the optical 


system as parallel to the principal axis. The 
Second Principal Focus is the point where the 
emergent rays cross each other when the inci- 
dent rays have been parallel to the principal 
axis. Negative Focus is the point from which 
rays of light appear, to, but do not come from, 
the focus of a minus lens. Secondary Focus. 
Any focus of the secondary axis. 

Fogging System. The system of fitting glasses by 
first making the patient artificially myopic by 
means of plus spheres, if they are not already 
myopic, the idea being to relax all accommoda- 
tion before using cylinders. 

Folders. A term employed for eye-glasses that 
can be folded up and placed in a small pocket. 

Follicle (fol'-ik-l). (L. folliculus = a small bag.) 
•A small secretory cavity or sac. 

Follicular (fol-ik'-u-lar). Containing follicles. F. 
Conjunctivitis. A form of conjunctivitis marked 
by the presence of follicles. This occurs gen- 
erally in children, and is characterized by the 
formation of small, clear elevations, consisting 
of adenoid tissue, in the conjunctiva of the 
lower lid; in some cases they are present also 
in tl e retrotarsal fold of the upper lid. 

Fontana, Spaces of. In the anterior chamber of 
the eye, where the corneal margin joins the 
base of iris and sclerotic, we find a number of 
delicate bands of tissue passing from the mem- 
brane of Descemet to the base of the iris. These 
are known as the ligamentum pectinatum iridis 
and between them small comb-like openings 
leading into Schlemm's Canal, known as the 



Foramen (fo-ray'-men). (L. foro == to bore a hole.) 
A hole or opening through any bone or a mem- 
branous structure. Infraorbital F., the external 
opening of the infraorbital canal, on the an- 
terior surface of the body of the maxilla; optic 
F., the opening between the lesser wing and 
body of the sphenoid transmitting the optic 
nerve and ophthalmic artery. (For other fora- 
men, see under orbit.) 

Force. (L. fortis = strong.) (Physics.) Any 
action between two bodies which changes, or 
tends to change, their relative condition as to 
rest or motion; or, more generally, which 
changes or, tends to change, any physical rela- 
tion between them, whether mechanical, chem- 
ical, or any other kind; as, the force of gravity. 

Fornix. (L. arch, vault.) A vault-like space. 

Fornix Conjunctiva. The turn or fold of the con- 

Fossae Patellaris (pa-tel-la'-ris) (meaning dish- 
like depression). The depression in the anterior 
surface of the vitreous body in which the crys- 
talline lens lies. Also called the Hyaloid Fossa, 

Tossa. (L. a ditch.) A pit, cavity or depression. 

Fovea (foh'-ve-ah). (L. fodio = to dig.) A small 
depression. F. Centralis is employed to desig- 
nate the little depression m the center of the 
macula lutea. 

I Fraction (frak'-shun). (L. f rangere = to break.) 
One or more of the equal parts of a unit. 

Frame Fitting. There are times when patients 
complain that their glasses are not comfortable, 
yet they have the right correction. The cause 



of the trouble is sometimes found in the im- 
proper adjustment of the frames. The fitting of 
a frame is very important, and if neglected will 
sometimes destroy the benefit of the most care- 
fully fitted lenses. When a student understands 
the relation between accommodation and con- 
vergence the value of frame fitting becomes 
easily understood. A convex lens, with its 
curved surfaces, may be described as made up 
of an infinite number of prisms with their 
bases meeting at the center: a concave lens, in 
a like manner, is made up of an infinite number 

Frame Fitting. 

of prisms with their bases outward. When a, 
person looks through the inner side of a convex 
lens, as he is compelled to do when the frames 
are too wide for the pupillary distance, he is 
looking not only through convex lenses, but 
also through prisms with their bases outward: 
when the frames are too narrow he looks 
through prisms with their bases inward. With 
concave lenses, of course, this condition will 
be reversed, and besides giving a prismatic 

effect, will cause the unbalancing of accommo- 
dation and convergence. 

The subject of frame fitting has always been 
and always will be more or less of a problem to 
the student, but after a little practice and care- 
ful attention it becomes a very easy matter. I 
will here mention a few points which may be of 
assistance to my fellow-student: 

1st. See that the pupillary distance is cor- 
rect and that the patient is looking through the 
center of lenses. If glasses are to be worn 
constantly it is best for the adjuster to stand 
off, say, about three feet, and direct the pa- 
tient to look between his eyes, so adjusting 
frames that the patient will be looking through 
the centers of lenses. For reading glasses the 
optical centers should be slightly closer and 
lower, and the top of the lenses must be in- 
clined forward, so as to be as near as possible 
at right angles to the line of vision. In this 
way better vision is enjoyed. 

2d. The lenses should be placed as near the 
eye as the lashes will permit. 

3d. Never prescribe a small lens for a large 
fiace nor a large lens for a small face, but 
always make the lenses as large as you possibly 
can without interfering with the patient's ap- 
pearance, and at the same time see that the 
pupillary distance is correct. In the fitting of 
spectacles see that the angle of crest saddles 
the nose nicely, and that the temples are long 
enough to go around the ear without showing 
underneath. See that the temples are not too 
far from the face and at the same rime do not 


press on the flesh. If you desire to tilt the 
lenses do not bend temples, but bend the end 
piece. All glasses should tilt outward from the 
top, but reading glasses more than distant ones. 
Cylinders should always be worn as spectacles, 
as it is very important that they should be held 
in their correct position. 

It is always best for one who is just com- 
mencing to practice to supply himself with a 
full set of measuring frames. They are put up 
and sold by all wholesale optical houses. The 
optical houses also supply cards on which are 
printed the various dimensions. Then by find- 
ing a sample frame among your set that about 
fits your patient you lay it down on the card, 
allowing for any change you wish to make, and 
you can easily figure the exact dimensions. 

Function (funk'-shun). (L. functio = to execute.) 
The special duties which an organ or group of 
organs has to perform. (Math.) A quantity so 
connected with another quantity that if any 
alteration be made in the latter there will be a 
consequent alteration in the former. Each 
quantity is said to be a function of the other. 
Thus, the circumference of a circle is a function 
of the diameter. 

Fundus (fun'-dus). That portion of a hollow organ 
farthest from the entrance. The fundus of the 
eye is seen by means of the ophthalmoscope, 
namely, the retina, blood vessels, choroid, optic 
disc, collectively. 

Fuscin (fus'-sin). (L. fuscus = dusky.) A brown 
pigment of the retinal epithelium. 


WANGLION (gang'-gle-on). (Gr. "a knot.") In 
anatomy, a knot-like aggregation of nerve cells. 
It Is a partly independent nerve center, with dis- 
tinct functions in connection with nearby struc- 
tures. Ciliary G., sometimes called ophthalmic 
or lenticular, is about the size of a pin's head, 
situated in the back part of the orbit, between 
the external rectus muscle and the optic nerve. 
The three nerves which enter it are, one from 
the nasal branch of the ophthalmic (sensory), 
one from a branch of the third nerve (motor), 
and a root of the sympathetic. From it passes 
off about ten filaments which pierce the poste- 
rior part of the sclera supplying the ciliary 
muscles, the iris, and the cornea. Gasserian or 
Semilunar G. lies in a depression (cavum 
Meckelii) oh the anterior surface of the petrous 
portion of the temporal bone near the apex. It 
is a flat expansion on the sensory root of the 
(fifth) trigeminal nerve, receiving on its inner 
side filaments from the carotid plexus of the 
sympathetic and giving off the ophthalmic, 
superior maxillary and inferior maxillary. The 
ophthalmic nerve is a sensor nerve. It supplies 
sensation to cornea, ciliary muscles, iris, lach- 
rimal gland, mucous membrane of nose, skin of 
eyelids, eyebrows, forehead and nose. Just be- 
fore entering the orbit, through the sphenoidal 
fissure, it divides into three branches, lachrimal, 
frontal and nasal. 

Geomeirical Center. A point midway between aJl 
edges. • 

Geometry. (Gr. geometria = to measure.) That 

100 LE^^'IS I»OCKET 

branch of mathematics which investigates the 
relations, properties and measurement of solids,, 
surfaces, lines and angles; the science which 
treats of the properties and relations of magni- 
tudes; the science and relations of space. 

Generic Compounds. Lenses having spherical 
and cylindrical curvatures of the same species; 
that is, both convex or both concave. Con- 
trageneric compounds have one surface convex, 
the other concave. 

Glabei'la, Glaberium. (L. glaber = smooth.) Space 
between the eyebrows. 

Gland. (L. glans = acorn.) The name applied to 
organs which separate from the blood any fluid 

Bruch's Glands. The lymph-follicles of the 
conjunctiva. Henle's Glands are a number of 
follicular cavities formed by irregular folds 
in the epithelium of the tarsal conjunctiva. 

Krause's Glands, the tubular glands which lie 
at the border of the tarsi near the fornix. These 
are regarded as accessory glands. Ciliary 
Glands are the sweat glands of the eyelids and 
located in several rows close to the free margin 
of the lid. They are also known as the Glands 
of Moll. Lachrimal Glands, the glands which 
secrete the tears. They are located in a depres- 
sion of the frontal bone at the upper and outer 
angle of the orbits. The gland is divided into 
two parts, the superior and inferior and at- 
tached to the bony roof of the orbit by the 
tarso-orbital fascia. The ducts, about ten in 
number, open into the fornix conjunctiva. Its 
nerve supply is the smallest of the three 


branches of the ophthalmic and known as the 
lachrimal nerve. Meibomian Glands (see Mei- 
bomian). Tarsal Glands (same as Meibomian). 

Glass. A hard, brittle, artificial substance formed 
by the fusion of silica, potash and lead. Under 
the best conditions it is quite transparent. 
Nothing definitely is known as to its origin. 
The Egyptians used it, and glass has been dis- 
covered amongst the ruins of Pompeii. 

The media out of which lenses are made. 
Crown glass for optical lenses, sometimes com- 
bined with flint glass. 

Glaucoma (glau-ko'-mah). (Gr. glaukos = green- 
ish gray.) A disease of the eye characterized 
by increased intraocular tension. In order to 
fully understand this disease it will be neces- 
sary to study thoroughly the anatomy of the 
eye, and in doing so pay particular attention 
to Schlemm's Canal and the Spaces of Fontana, 
situated in the first tunic between the sclerotic 
and cornea. These canals are said to carry 
away the excess of aqueous humor. The theory 
most generally accepted is, that the vitreous 
humor is formed in the choroid and ciliary body 
and passes through the hyaloid membrane into 
the vitreous cavity; from there it filters through 
the suspensory ligaments into the posterior 
chamber, where it becomes watery, and is 
known as the aqueous humor. After passing 
through the pupil into the anterior chamber it 
is said to pass through the Spaces of Fontana 
into Schlemm's Canal. In this way one can 
readily see that if the iris was attached to the 
lens, as it is in cases of iritis, or by the strain- 
ing of the ciliary muscles, as m hypermetropia, 


thus closing the Spaces of Fontana, the drain- 
age system would be blocked, while the humors 
continue forming, resulting in .a painful intra- 
ocular pressure. Glaucoma may be divided into 
two kinds, primary and secondary. Primary, 
when it makes its appearance in a healthy eye, 
or with a disease like cataract. Secondary, 
Avhen caused by a disease like iritis. It is a 
progressive disease, and unless checked by 
treatment ends in permanent blindness. 

Symptoms of Glaucoma. (1) Pain, sometimes 
of a neuralgic character. (2) Increased tension 
of the eyeball, sometimes becoming stonelike. 
(3) Rapid failing of the power of accommoda- 
tion. (4) Dimness of vision. The pupil is 
dilated and sluggish. (.5) The patient complains 
of seeing flashes of light and colored halo 
around a flame or candle. (6) Cupping of the 
optic disc. (7) Conjunctivitis. The iris also 
appears steamy. When glaucoma is suspected 
the patient should be sent to an oculist at once. 

The use of atropine causes the iris to crowd 
into the periphery of the anterior chamber, 
somewhat occluding the Spaces of Fontana and 
interfering with the free exit of aqueous humor. 
As the intraocular tension increases, the stop- 
page becomes more complete. When the atro- 
pine is discontinued the sphincter muscle of the 
pupil draws the iris away from the Spaces of 
Fontana and the normal outlet is again opened. 
As age advances, the sphincter loses its power, 
and frequently in old people fails to pull the iris 
away from the Spaces of Fontana, and this con- 
dition may result in glaucoma. For the reasons 


mentioned it is, as a rule, unsafe to use atro- 
pine after the ages of from 30 to 35. 

Glaucomatous (glau-korn'-at-ous.) Of the nature 

of glaucoma. 
Glioma (gly-oh'-mah). (Gr. glia = glue + oma.) 

A malignant tumor of the retina. 

Gllosarco'ma. Glioma combined with sarcoma. 
Globulin (glob'-u-lin). (L. globulus = globule.) A 
proteid from the lens. 

Goggles. Spectacles with wire screens for the 

Goiter (goi'-ter). (L. guttur = throat.) An en- 
largement of the thyroid gland. Exophthalmic g. 
(See Exophthalmic Goiter.) 

Gonorrhe'al Ophthalmia. (Gr. gonos = semen -h 
rhoia = a flow. Ophthalmus = eye.) The most 
acute form of purulent conjunctivitis. It is 
caused by the Introduction of the urethral dis- 
charge to the conjunctival sac. 

Graduated Tenotomy. (L. gradus = a degree. Gr. 
tenon = tendon -f tome = incision.) An incom- 
plete cutting of the tendon of an eye muscle. 

Granular Lids (Trachoma). (L. granulum, dim of 
granum ^= grain.) Roughness and soreness of 
the inside of the eyelids. This roughness is 
caused by a swelling of the lymph-corpuscles, 
forming, as it were, little lymphatic glands or 
lymphatic follicles. 

Gran'ule. A small rounded body. G. Layer, one 

of the layers of the retina. 

Gravity (grav'-i-ty). (L. gravitas = heavy.) The 
state of having weight. (Physics.) The ten- 
dency of a mass of matter toward a center of 


attraction. Specific gravity, the ratio of the 
weight of a body to the weight of an equal 
volume of some other body taken as the stand- 
ard or unit. This standard is usually water for 
solids and liquids, and air for gases. Thus, 19, 
the specific gravity of gold, expresses the fact 
that, bulk for bulk, gold is 19 times as heavy as 

Gravitation (grav-i-ta'-shun). The act of gravi- 
tating. (Physics.) That kind of attraction or 
force by which all bodies in the universe tend 
toward each other. 

Groove (groov). A furrow, crease or sulcus. A 
narrow, elongated depression on any surface. 
Lachrimal G., the bony channel which lodges 
the lacrimal sac. It is located at the anterior 
and inner part of the orbit; cavernous G., car- 
otid sulcus, the groove on the upper surface or 
the sphenoid bone, supporting the cavernous 
sinus and the carotid artery; optic G., a groove 
on the upper surface of the sphenoid bone be- 
tween the optic foramen in which rest the optic 


ALLER'S CIRCLES. Arterial and venous 

circles within the eye. 
Halo. (Gr. halos = a circular threshing floor.) A 

reddish yellow ring surrounding the optic disc. 
Ha'lo Glaumato'sus. A whitish ring around the 

optic disc in glaucoma. 
Ha'lo Symptom. Seeing of colored rings around 

lights. This is a symptom of incipient glaucoma. 
Hec'tometer. One hundred meters. 


Helcol'ogy. (Gr. helkos = ulcer + logia = study.) 
Science of ulcers. 

Helco'sis. (Gr. helkos — ulcer and suffix osis = 
condition.) The formation of an ulcer. 

Hemeralopia (hem-er-a-lo'-pi-ah). (Gr. hemera -- 
day -f alaos =^ obscure + ops eye.) Day blind- 
ness, better vision in a dim light. 

Hemiachromatopsia (hem-i-a-chro-mat-op'-si-ah ) . 
(Gr. hemi — half -f- a ^ without + chroma ^^ 
color + opsis — vision.) Color blindness in one- 
half, or in corresponding halves, of visual field. 

Hemianopia (hem-i-an-o'-pi-ah). Hemianopsia. (Gr. 
hemi ^- half + an without + opsis — vision. ) 
Blindness for one-half the field of vision in one 
or both eyes. 

Hemiopic (hem-e-op'-lk) ("half vision"). That 
condition of the eye in which only half of the 
object is seen. 

Hemophthal'mla, Hemophthal'mus. (Gr. haima =- 
blood -f ophthalmos = eye.) Extravasation of 
the blood inside of the eye. 

Hemorrhage fhem'-or-aj). (Gr. haima -^ blood + 
rhagia to burst.) Escape of blood from the 
veins or arteries. 

Hering's Theory. This is a doctrine which holds 
that color-perceptions are dependent on a visual 
substance in the retina, which is variously mod- 
ified by anabolism for black, green, or blue, and 
by catabolism for white, red and yellow. 

Heterochromia (het-ero-kro'-me-ah). (Gr. heteros 
other -f chroma color.) A difference iu 
color (in the irides or of different parts of the 
same iris J. 


Heterometropia (het-er-o-me-tro'-pi-ah). (Gv. het- 
eros = other + metron = measure -f ops = 
eye.) That condition in which the refractive 
power is unlike in the two eyes. 

Heteronymous (het-er-on'-im-us). (Gr. heteron- 
ymos = having a different name.) Crossed. 
See Diplopia. 

Heterophoral'gia. Pain with heterophoria. 

Heterophoria (het-er-o-pho'-ri-a). (Gr. heteros = 
other + phoria = tending.) That condition of 
the eyes in which the visual axes, although 
parallel when in use for distant vision, deviate 
in another direction when the extrinsic muscles 
are in a state of rest. It is subdivided into 
eight kinds. When the eyes have a tendency 
to turn in it is known as esophoria; if a ten- 
dency to turn out, it is known as exophoria; if 
a tendency to turn up, it is known as hyper- 
phoria; if up and in, hyperesophoria, and if up 
and out, hyperexophoria; if a tendency down- 
ward, it is known as cataphoria; and if down 
and in, esocataphoria; if down and out, exocata- 
phoria. Any error of refraction is liable to 
bring on Heterophoria, and by correcting the 
error, the Heterophoria may disappear, though 
it may linger for a month or two. Again one 
muscle may be too short or too long and a 
prism will have to be worn, thus allowing the 
eyes to deviate in order to avoid strain. 

Heterophthal'mos. (Gr. heteros = other + oph- 
thalmos = eye.) That condition in which the 
irides differ in color. 

Heterotropia (het-er-o-tro'-pi-a). (Gr. heteros = 
other + trope = I turn.) A condition in which 


the extrinsic muscles are no longer able to hold 
the eyes parallel and there is a positive and 
visible appearance of their deviating. They 
may turn in any direction, as in heterophoria; 
if upward, hypertropia; if downward, hypotro- 
pia or catatropia; if inward, esotropia; if out- 
ward, exotropia. For permanent deviation, see 

Hippus (hip'-us). (Gr. hippos = horse so named 
from its irregular movement.) Spasmodic 
pupillary movements, independent of the action 
of light. 

Histology (his-toF-o-je). (Gr. histos = tissue + 
logia = discourse.) The science of the minute 
structure and composition of tissues. 

Holmgren's Test (holm'-grens). A color test with 
a number of different colored yarns represent- 
ing the various shades of different colors. Used 
for detecting color blindness. 

Homocentric Rays (ho-mo-sen'-tric). (Gr. homos = 
same -[- kentron = center.) A conic pencil of 
light rays. 

Homonymous. (Gr. homonymos = of the same 
name.) See Diplopia. 

Hordeolum (hawr-dee'-o-lum). (L. hordeum = 
barley.) Sty; inflammation of sebaceous glands 
of the eyelid. 

Horizon (ho-ri'-zun). (L. horizon = the boundary 
line.) The circle which bounds that part of 
the earth's surface visible to a spectator from 
a given point; the apparent junction of the 
earth and sky. 

Horizontal Line (hor-i-zon'-tal.) A constructive 
line, either drawn or imagined, which passes 


through the point of sight, and is the chief line 
in the projection upon which all verticals are 
fixed, and upon which all vanishing points are 
found. Horizontal plane is a plane parallel to 
the horizon, upon which it is assumed that ob- 
jects are projected. 

Horny Epithelium. Trachomatous conjunctivitis. 

Horopter (ho-rop'-tur). (Gr. horos = limit + 
opter = one who sees.) The field of binocular 
vision as seen with the eyes fixed. 

Hot Eye. Temporary congestion of the eye. This 
is seen in gouty patients. 

Humor. (L. humere = to be moist.) A fluid ele- 
ment of the eye. (Aqueous, crystalline lens and 

Hutchinson's Pupil. One that is dilated on one 

Hiyaline (hi'-al-in). (Gr. hyalos = glass.) Glassy. 

Hyalitis (hy-al-i'-tis). Inflammation of the vitre- 
ous humor or hyaloid membrane. 

Hyaloid (hy'-al-oid). (Gr. hyalos = glass -f eidos = 
resemblance.) That which resembles glass in 
its transparent qualities. Hyaloid membrane 
surrounds and encloses the vitreous humor and 
forms the suspensory ligaments. 

Hyaloid Artery. The fetal branch of the central 

artery of the retina. 
Hyaloid Canal, or Canal of Stilling. The canal 

through the vitreous body, occupied by the 

hyaloid artery during fetal life. 

Hyaloid Fossa. (Gr. hyalos = glass + L. fossa = 
ditch.) The depression in the anterior surface 


of the hyaloid membrane in which the crystal- 
line lens lies. 

Hyaloid Membrane. The delicate transparent 
membrane which forms a sac and contains the 
vitreous humor, and forms the suspensory liga- 
ments of the lens and the Zone of Zinn. 

Hydrophthalmia (hy-drof-thal'-mi-ah), Hydroph- 
thalmus. (Gr. hydro = water + ophthalmos = 
eye.) Increase in the fluid contents of the eye. 

Hydrops (hi'-drops) (dropsy). An abnormal col- 
lection of fluid in any part of the body. 

Hygroma (hi-gro'-mah). (Gr. hygros = fluid -1- 
oma = tumor.) A sac or cyst filled with fluid. 

Hyperaesthesia (hi-per-as-the'-si-ah). (Gr. hyper = 
overmuch + aisthesis = sensation.) Over-sensi- 
tiveness. H. of Retina, over-sensitiveness of 
the retina. 

Hyperchromatism (hy'-per-chro'-ma-tism). (Gr. hy- 
per = overmuch + chroma = color.) Having an 
unusual intensity of color. 

Hyperemia (hi-per-e'-me-ah). (Gr. hyper =over -f- 
haima = blood.) A condition where there is an 
abnormal fullness of the blood vessels. H. of 
the eyelids is often a forerunner of inflamma- 
tion. It is usually accompanied by a slight 
marginal blepharitis and even conjunctivitis, 
and if these are relieved the hyperemia to a 
great extent will disappear. 

Hyperkeratosis (hy-per-ker-at-o'-sis). Hypertrophy 
of the cornea. 

Hypermetropia (hy-per-me-tro'-pi-ah). (Gr. hy- 
per = over + metron = measure -f ops = eye.) 
(Far sighted.) An error of refraction, where 


parallel rays of light focus back of the retina 
with the muscles of accommodation at rest, due 
to the shortness of the eye from before, back 
or insufficient curvature of the dioptric media. 
Subdivided into three classes — latent, manifest 
and total. Latent h. has no subdivisions; it is 
hypermetropia that is hidden by cramp of the 
ciliary muscle, and will not relax without the 
use of drugs at the time of fitting, but when 
the correction for the manifest is worn, the 
cramp begins to relax and more hypermetropia 
becomes manifest. It may take a week or a 
year. Manifest h. is that part found and cor- 
rected with the trial case and retinoscope. It 
is said to have three subdivisions, namely, 
facultative, relative and absolute. Facultative h. 
is where the patient has the ability to overcome 

A hypermetropic eye. The heavy lines show the focus 
of parallel rays behind the retina. The dotted lines 
«how the effect of accommodation upon the same rays. 

his error by accommodation, and sees well at 
all distances. Glasses relieve strain, but do not 
improve vision in this case. Relative h. is where 
it is possible to accommodate for a near point, 
by converging to a point still nearer — in fact, 
by squinting. This eye has blurred vision for 
close work, and plus spheres improve vision. 


Absolute h. is where the error exceeds the 
amount of the accommodation, and the patient 
is unable to bring the focus to the retina, and 
vision is blurred at all distances. The correc- 
tion always improves vision. Total h. is the full 
amount of hypermetropia the patient has. For 
instance, we correct the eye with the trial case 
and find 2-D. of manifest; then by the use of 
drugs relax any cramp; and now find that the 
same eye has 6-D. of hypermetropia. 4-D. was 
hidden by cramp. This we call latent, 6-D., 
being the total amount of hypermetropia. 

Hyperope (hi'-per-op). A person who has hyper- 

Hyperopia (hi-per-o'-pe-ah); (Gr. hyper = over + 
ops = eye.) See Hypermetropia. 

Hyperphoria (hyper- fo'-ri-ah). (Gr. hyper = 
above -f phoria = tending.) That condition in 
which one of the eyes, although parallel with 
its fellow when in use for distant vision, devi- 
ates upward when the extrinsic muscles are in 
a state of rest. 

Hyperplasia (hi-per-pla'-ze-ah). (Gr. hyper = 
above + plasis = a moulding). Excessive tissue 

Hypertrophy (hy-per'-tro-fy), (Gr. hyper = above 
+ trophe = nourishment.) An abnormal in- 
crease in the size of a part or an organ. 

Hypertropia (hy-per-tro'-pi-ah). (Gr. hyper = 
above + trope = turn.) Elevation of one visual 
axis above the other. 

Hyphemia (hi-fe'-me-ah). (Gr. hypo = below -f- 
haima = blood.) Hemorrhage within the eye. 


Hypnogenet'ic. (Gr. hypnos = sleep + genesis = 
production.) Causing or producing sleep. 

Hypnolepsy (hip'-no-lep-se). (Gr. hypnos ^= sleep 
+ lepsis = a seizing.) Abnormal sleepiness. 

Hypometropia (hy-po-me-tro'-pi-ali). (Gr. hypo = 
under 4- metron = measure + ops = eye.) See 
Myopia and Brachymetropia. 

Hypophoria (hi-po-fo'-re-ah). (Gr. hypo = below + 
phoria = tending.) That condition in which one 
of the eyes, although parallel with its fellow 
when in use for distant vision, deviates down- 
ward when the extrinsic muscles are in a state 
of rest. 

Hypopyon (hi-po'-pe-on). (Gr. hypo = beneath -|- 
pyon = pus.) Pus in the anterior chamber of 
the eye. 

Hypotenuse (hi-pot'-e-nus). (Gr. hypo = under + 
teinein = to stretch.) The side of a right- 
angled triangle opposite the right angle. 

Hypotonia (hi-po-to'-ne-ah). (Gr. hypo = under + 
tonos = tone.) Diminished intraocular tension. 

Hypotonus (hi-pot'-o-nus). See Hypotonia. 

Hypotony (hi-pot'-o-ne). See Hypotonia. 


DENTICAL POINTS. When the image falls on 
corresponding points on the retinae of the two 

IHaqueation (il-lak-we-a'-shun). (L. illaqueare = 
to ensnare.) The curing of ingrowing eye- 
lashes by drawing with a loop. 

Illumination (il-lu-min-a'-shun). (L. illuminare = 
to light up.) The lighting up of a place or ot- 

ject for inspection. Focal i., when light is 
brought to a focal point by lens or mirror. 
Axial i., when light is transmitted or reflected 
along the axis of a lens. Direct i., light thrown 
directly upon the object. Oblique i., when an 
object is illuminated from one side. 

Illusion (il-lu'-shun). (L. illudere = to mock.) An 
unreal image presented to the mental vision. 

Image (im'-ej). (L. imago = likeness.) A picture 
or conception of anything real. Aerial i., image 
seen as in the air by the ophthalmoscope. Di- 
rect i., Erect i., and Virtual i., formed by rays 
not yet focused. An upright image. False !., 
image formed on the retina of the deviating eye 
in strabismus. Optical I., an appearance of an 
object created by refraction or reflection. 

Imbalance. That condition in which the eyes 
tend to deviate from parallelism with the ex- 
trinsic muscles in a state of rest. See hetero- 

Inadequacy. (L. in = not + adaequare = to be 
equal.) Unable to perform allotted function. 

Incident. (L. incidere =^ to fall into or upon.) 
Falling or striking upon, as a ray of light upon 
a reflection surface. 

In'cident Ray. The name given to a ray of light 
before it strikes the second medium. 

Index of Refraction. The refracting or bending 
power of the medium as compared with air, the 
normal standard, and the index of which is the 
unit 1. Water as compared with air is 1.33; 
crown glass, 1.52; flint glass. 1.62 + ; pebble. 
1.54; diamond, 2.4, the greatest index of any 
known medium. The transparent parts of the 


eye in their order are as follows; the cornea, 
1.33; the aqueous humor, 1.33; the crystalline 
lens, 1.43, and vitreous humor, 1.33. Different 
indices of refraction would mean different den- 

Induction (in-duk'-shun). (Physics.) The prop- 
erty by which one body, having electrical or 
magnetic force, induces it in another body with- 
out direct contact. 

Inertia (in-er'-shi-a). (L. idleness.) (Physics.) 
That property of matter by which it tends when 
at rest to remain so, and when in motion to 
continue in motion, and in the same straight 
line or direction unless acted upon by some 
external force. 

Infiltration (in-fil-tra'-shun). (L. in, and filtrare = 
to filter.) The act or process of infiltrating a 
fluid into the cellular tissue. 

Infinite Distance. When rays of light proceed 
from a distance of twenty feet or more they are 
considered parallel, and are said to come from 

Inflammation (in-flam-ma'-shun). (L. inflammare = 
to burn.) A diseased condition characterized by 
redness, pain, heat and swelling. Traumatic i., 
that which follows a wound or injury. 

Inflection (in-flek'-shun). (L. in = in + flectere = 
to bend.) The act of bending inward or that 
state of being bent inward. 

Infra. A prefix denoting a position below the 
part denoted by the word to which it is joined. 

Infraductlon, Deorsumvergence. The act or power 
of turning one eye downward from its fellow. 



Infraorbital (in-fra-or'-bi-tal). Situated beneath 
the orbit. 

Innervation (in-nerv-a'-shun). (L. in = not + 
nervus = nerve.) The sending of nervous stimu- 
lus or power to an organ through its nerves. 

Innervate (in-nerv'-et). To supply with nerves; 
to give nervous stimulus to. 


Amblyoscope. An instrument to stimulate, 
exercise and develop the fusion faculty in stra- 
bismus, or squinting patients. 

Color Test (Holmgren's). A set of worsteds, 
consisting of various shades and tints, for test- 
ing color blindness. 

Focimeter (fo-sim'-e-ter). An instrument for 
measuring the focal lengths of lenses or com- 
bination of lenses. 

Keratometer. See Ophthalmometer. 

Kryptoscope. An instrument used for testing 
strain in ophthalmic lenses. With this instru- 
ment strain can be detected in fused (kryptok) 
lenses or when the screw holding a lens in its 
frame is too tight. 

Latest Optometer. An instrument combining 
the advantages of a fixed and revolving cell 


trial frame, Stevens Phorometer, Rotary Prism 
and Maddox Multiple Rod. 

Myometer (my'-o-meter). An instrument for 
diagnosing and correcting muscular insufficiency 
at the near point of vision. 

Ophthalmoscope. An instrument with which 
the interior of the eye may be examined. Also 
the dioptric and pathological states may be de- 
termined. There are many different kinds of 
ophthalmoscopes; for instance, the Loring is 
a small hand affair, which contains a mirror 
and a number of lenses; the self-luminous, by 
DeZeng, also a hand instrument; and the com- 
bined ophthalmoscope and retinoscope, a com- 
bined instrument for indirect ophthalmoscopy 
and for retinoscopy. This is a large machine 
which stands on a table. 

Ophthalmometer or Keratometer. An instru- 
ment for determining the amount and axis of 
corneal astigmatism, an objective test. 

Ophthalmometroscope. An ophthalmoscope 
with an attachment for measuring the refrac- 
tion of the eye. 

Perimeter. An instrument for measuring the 
visual field. 

Punctumeter. A simple instrument for deter- 
mining the far point and the near point, there- 
fore the amount of hypermetropia, myopia, or 
presbyopia. It also indicates the age of the 

Savage Monocular Phorometer and Cycio 
Phorometer. Two instruments which together 
make a complete appliance for measuring all of 
the muscles of the eye. 

Skiascope. A frame with a serie«? of plus and 

OPHTHA L:\IIC dictionary 1J7 

minus spherical lenses, to be used in place of 
test frame and lenses when refracting a patient 
by retinoscopy. 

Stevens Phorometer. An instrument for 
measuring muscular imbalance. 

Stigmatometer. An instrument for testing re- 
fraction of the eye by the objective method. 
Also a complete ophthalmoscope for the direct 
Insufficiency. Incapacity of normal action within 
the eye. 

integer (in'-te-ger). (L. a whole number.) 

Intercilium (in-ter-sir-e-um). (L. inter = be- 
tween + cilium = eyelid.) The space between 
the eyebrows. 

Interorbital (in-ter-or'-bi-tal). Situated between 
the orbits. 

Inter'nus. Internal. The internal rectus muscles 
of the eye. 

Interval. (L. inter = between + vallum = wall.) 
Sturm's, or Focal i. In astigmatism, is the dis- 
tance between the two foci, at which the prin- 
cipal meridians meet. 

Intraocular (in-trah-oc'-u-lar). Situated within the 
globe of the eye. 

Intraocular Tension. Pressure from the fluids 
within the eye. 

Intraorbital (in-trah-or'-bit-al). Situated within 
the orbit. 

Involution (in-vo-lu'-shun), (L. involvere = to roll 
up.) Multiplication of a quantity into itself any 
number of times. 

Ir'idal. Pertaining lo the iris. 


Iridectome (ir-id-ek'-tom). An instrument used 
in cutting the iris in iridectomy, 

Iridectomize (ir-id-ek'-tom-ize). To cut away a 
part of the iris. 

Iridectomy (ir-id-ek'-to-my). (Gr. iris + ektome = 
excision.) The operation for removing a piece 
from the iris for the relief of tension of the 
eyeball in the case of glaucoma, thus producing 
an artificial pupil. 

Iridencleisis Hr-id-en-cli'-sis). (Gr. iris + enkleio == 
to enclose.) An operation for displacing the 
pupil from its natural position, brought about 
by drawing the iris into a wound made near the 
periphery of the cornea, and causing it to be- 
come adherent there. 

Irideremia (ir-id-er-e'-mi-ah). TGr. iris + eremia = 
to deprive.) Defect or imperfect condition of 
the iris. 

Irides (ir'-id-ez). Plural of iris, 

Iridesis (ir-id'-e-sis), (Gr. iris + desis = to bind.) 
Strangulation of a part of the iris to form an 
artificial pupil. 

Iridescent Vision. (Gr. iris ^ rainbow.) That con- 
dition in which variously hued borders are seen 
surrounding artificial light. 

Iridic (i-rid'-ik). Pertaining to the iris. 

Iridoavulsion (ir'-i-doh-a-vul'-shun). A term ap- 
plied to the total removal of the iris when it ie 
completely torn from its periphery. 

Iridocele (i-rid'-o-se'e). (Gr. iris + kele = hernia.) 
Hernial protrusion of a slip of the iris. 

Iridochoroiditis (ir-id-o-ko-roid-i'-tis). Inflamm?> 
tion of the iris and choroid. 


Iridocinesis ( ir-id-o-sin-e'-sis). The movement of 
the iris in contracting and expanding. 

Iridocyclitis (ir-id-o-syc-li'-tis). (Gr. iris + kyklos 
= circle + itis = inflammation.) Inflammation 
of the iris and ciliary body. 

Iridod'esis. That condition in which a loop of iris 
is drawn out, and strangulated by a fine ligature 
tied around it over the incision; the little loop 
soon drops off, and the result is a pear-shaped 
pupil, with its broad end toward the center. 

iridodialysis (ir-id-o-di-al'-ys-is). (Gr. iris + dialy- 
sis = separation.) Separation of the iris from 
the ciliary body. 

Irldodonesis (ir-id-o-do-ne'-sis). (Gr. iris -{- doneo = 
agitation.) Trembling condition of the iris. 

Iridoncus (ir-id-on'-kus). (Gr. iris + onkos = 
swelling.) A tumor or swelling of the iris. 

Iridoperiphacitis (ir-id-o-per'-i-fa-si'-tis). (Gr. iris 
+ peri = around + phakos = lens.) Inflamma- 
tion of'the capsule of the lens of the eye. 

Iridoplania (ir-id-o-pla'-ni-ah). (Gr. wandering.) 
Trembling of the iris; irldodonesis. 

Iridoplegia (ir-id-o-ple'-gi-ah). (Gr. iris + plege = 
stroke.) Paralysis of the iris. Without defect 
of accommodation, it usually affects only the 
action to light, reflex iridoplegia, the associated- 
action remaining. It occurs as a very early 
symptom in locomotor ataxia, sometimes with- 
out any other symptoms of that disease, and 
should always lead to full investigation. It is 
probably due to degeneration in that part of 
the nucleus of the third nerve which presides 
over the reflex action of the pupil. 


Iridorrhexis (ir-id-or-rhex'-is). (Gr. iris + rhexis = 
rupture.) Rupture of the iris. Tearing away of 
the margin of the iris. 

Iridosclerot'omy. (Gr. iris + tome = incision.) 
Puncture of the sclerotic and of the edge of the 

Iridotomy (ir-id-ot'-o-my). (Gr. iris + tome = 
incision.) The operation whereby an artificial 
pupil is formed by the natural gaping of a sim- 
ple incision in the iris. Iridotomy is most use- 
ful when the iris has become tightly drawn 
toward the operation scar by iritis occurring 
after a cataract has been removed. 

Iris. (Gr. rainbow.) So called from its resem- 
bling the rainbow in its many colors. The 
membrane, stretched vertically in the anterior 
part of the eye, in the aqueous humor, in which 
it forms a flat circular partition separating the 
anterior from the posterior chamber. It is the 
anterior part of the second tunic, and is per- 
forated by a circular opening called the pupil, 
which is constantly varying in size, owing to the 
contractions of its two sets of muscles. Its 
posterior surface is covered with a black coat 
of pigment which continues backward over the 
ciliary body and choroid. The greater circum- 
ference of the iris is adherent to the ciliary 
body and to the sclerotic by the ciliary liga- 
ment. (Ligamentum Pectinatum Irides.) Its 
arteries are from the long ciliary arteries, which 
form two circles, one broad near its circumfer- 
ence, the other small and seated around the 
circumference of the pupil. Its veins empty 
into the long ciliary veins and into the Vena 
Vortisosea. The pupil is contracted by the cir- 


cular or sphincter muscle supplied by the motor 
oculi (3d) nerve and dilated by the radiating 
muscle or dilator, which is chiefly supplied by 
the sympathetic. The iris gives the eye its 
color, regulates the amount of light which 
enters and prevents spherical aberration of the 
crystalline lens. 

Iris Shadow. The test for maturity, or ripened 
cataract; created by oblique illumination. 

Iritic (i-rit'-ik). Pertaining to the iris. 

Iritic Angle. The angle formed by the junction of 
the iris and cornea. 

Iritis (i-ri'-tis). (Gr. iris + itis = inflammation.) 
Inflammation of the iris, which is usually caused 
by certain specific blood diseases. It often 
occurs in the course of ulcers and of wounds 
and other injuries of the cornea; also with 
sclerotitis and keratitis. 

Irregular Astigmatism. See Astigmatism. 

Irritant. (L. irritare ^ to provoke.) Causing irri- 

Ischemia (is-ke'-me-ah). (Gr. ischo = restrain + 
haima = blood.) Bloodlessness. 

Ischemia Retinae (is-ke'-me-ah). Diminution of 
arteries in the retina. 

I so. (Gr. isos equal.) A prefix denoting equality. 

Isocoria (i-so-co'-ri-ah). (Gr. isos = equal + kore 

= pupil.) Where the pupils in the two eyes are 


Isometropia (i-so-met-ro'-pi-ah). (Gr. isos = equal 
-f metron = measure* + ops = eye.) The state 
in which both eyes are alike in their refraction. 


Isosceles (i-sos'-e-lez). (Gr. isos = equal + skelos 
= leg.) Having two sides equal. 

Isotropic (trop'-ik). (Gr. isos =equal + trope = a 
turning.) Equal in refractive power. 

el ACER'S TEST TYPE. The standard type for 
close reading, a hand chart. 

Joffroy's Symptom. That condition which exists 
when patient suddenly turns his eyes upward 
and there is absence of facial contraction; seen 
in exophthalmic goiter. 


ATAPHORIA (kat-a-phor'-ia). (Gr. kata = 
down + phoria = tending.) That condition in 
which the eyes turn downward when the ex- 
trinsic muscles are in a state of rest. Stevens 
gives 50° for the maximum depression of nor- 
mal eyes 

Keratalgia (ker-at-al'-je-ah). (Gr. keras = horn -+- 
algos = pain.) That condition in which there is 
pain in the cornea. 

Keratectasia (ker-at-ek-ta'-si-ah). (Gr. keras = 
horn -f ektasis = extrusion.) That condition in 
which the cornea protrudes. 

Keratitis (ker-at-i'-tis). (Gr. keras = horn + itis 
= inflammation.) Inflammation of the cornea. 

Keratocele (ker-at'-o-cele). (Gr. keras = horn -!- 
kele =^ hernia.) Corneal protrusion of Desce- 
met's Membrane. 

Keratoconus (ker-at-o-ko'-nus). (Gr. keras = horn 


-f- konos = cone.) That condition in which there 
is a conical cornea. 

Keratoglobus (ker-at-o-glo'-bus). (Gr. keras == 
horn + L. globus = ball.) A globular protru- 
sion of the cornea. 

Keratohelcosis (ker-at-o-hel-ko'-sis). (Gr. keras = 
horn + helkosis = ulceration.) That condition 
wherein there is ulceration of the cornea. 

Keratoiri'tls. (Gr. keras = horn + itis = inflam- 
mation.) That condition wherein the cornea 
and iris are inflamed. 

Keratoma. (Gr. keras = horn -f oma = tumor.) 
A horn-like tumor or swelling. 

Keratomalacia (ker-at-o-ma-la'-she-ah). (Gr. keras 
= horn + malakia = softness.) Softening of 
the cornea. 

Keratome (ker'-at-om). A knife for incising the 

Keratometer (ker-at-om'-e-ter). (Gr. keras = horn 
— metron = measure.) An instrument used for 
measuring the cornea. It is commonly called 
the ophthalmometer, of which there are several 
different makes. 

Keratometry (ker-at-om'-e-try) . Measurement of 
corneal curves. 

Keratomycosis (ker-at-o-my-ko'-sis). (Gr. keras = 
horn (cornea) -f mykes = fungus.) Fungous 
disease of the cornea. 

Keratonyxis (ker-at-o-nik'-sis). Gr. keras = horn 
->- nyxis = a pricking.) Puncture of the cornea. 

Keratoplasty (ker'-at-o-plas-ty). (Gr. keras = horn 
-f plasso = I form.) Plastic surgery of the 

1:^4 i^KWiS Jr'UCKHJT 

Keratoscleritis (ker-a-to-skle-ri'-tis). (Gr. keras = 
horn + sclera + itis.) Inflammation of both 
cornea and sclera. 

JKeratoscope (ker'-at-o-scope). (Gr. keras = horn 
+ skopeo = I examine.) Instrument for exam- 
ining the cornea. 

Keratoscopy (ker-at-os'-ko-pe). Examination of 
the cornea with a keratoscope. Skiascopy, 

Kerectomy (ke-rek'-to-me). (Gr. keras = horn -f 
ectome ^ excision.) Removal of part of the 

Kilometer. One thousand meters. 
Kopiopia or Copiopia (ko-pee-oh'-pee-ah). (Gr. 
kopos = fatigue + ops = eye.) See Asthenopia. 

Korectomia or Corectomia (ko-rek-to'-mee-ah). 

(Gr. kore = pupil + extome = excision.) The 

operation for artificial pupil by removal of a 

part of the iris. 
Korectopia (kor-ek-to'-pe ah). (Gr. kore = pupil 

+ ektopos = out of place.) Displacement of the 


Koroscopy (ko-ros'-ko-pee). (Gr. kore = pupil + 
skopeo = I view.) See Retinoscopy. 

Kryptok. (L. crypta = a vault; a hidden place.) 
The name applied to a bifocal lens made by 
fusing two pieces of glass of different density 
together, so as to become one integral piece 
with no visible line of demarcation. 

Lachrymal (lak'-rim-al). (L. lacrimal a 
tear.) Pertaining to tears. 

Lachrymal Apparatus. Consists of the lachrymal 


gland which secretes the tears and the cxsecre- 
tory ducts which convey the fluid to the surface 
of the eye. This fluid after passing over the eye 

runs through the puncta into the lachrymal 
canal, then to the lachrymal sac and along the 
nasal duct into the cavity of the nose. 
Lachrymation (lak-rim-a'-shun). The secretion 
and discharge of tears. 

Lachrymotomy (lak-rim-ot'-o-my). (L. lacrima 
a tear -|- G. tome =^ incision.) Operation for in 
cision of lacrimal duct or sac. 

Lacrimal Gland. See Gland. 

Lacrimal, Lacrymal. Same as Lachrymal. 

Lacu'nar Orbitae. The roof of the orbit of the eye. 

Lacus. ( L. "a lake.") The small circular portion 
at the nasal side of the opening between the 

La'cus Lacrima'lis. (L. "lake" + lacrima -- a 
tear.) The triangular space at the inner can- 
thus between the two eyelids. 

Laevophoria (le'-vo-phor'-ia). (L. laevus ^ left -^ 
G. phoria =^ tending.) That condition in which 


the eyes turn to the left when the extrinsic 
muscles are in a state of rest. 

Lagophthalmus (lag-of-thar-mus). That condition 
In which it is impossible to close the eyes! 

Lamella (lam-el'-ah). (L. dim. of lamina ^ plate.) 
A thin plate or scale. Lamina. 

Lamina (lam'-in-a). (L. "a plate.") A layer con- 
sisting" of a flat, thin membrane. 

Lamina Crlbrosa (lam'-in-a crib-ro'-sa). (L. "a 
plate" -f- cribrum = sieve-like.) The perforated 
area in the sclerotic of the eye through which 
the optic nerve fibers pass to form the retina. 

Lamina Fus'ca. (L. "a plate" + fuscus = brown.) 
The outside layer of the choroid. 

Landolt, Edmund, M. D. Ophthalmologist, born in 
Aaran, Switzerland, in 1846; pursued his profes- 
sional studies in the universities of Heidelberg. 
Vienna, Berlin, Utrecht and Zurich, graduating 
from the latter in 1869; then worked for more 
than a year as Horner's assistant in the Zurich 
clinic for eye diseases; in 1874 he established 
himself in Paris as an ophthalmologist. His in- 
vestigations in his specialty have been distin- 
guished by their originality. Among his works 
are "On the Retina," "A Manual of Ophthal- 
moscopy," published in French, English, Ger- 
man and Spanish; "The Refraction and Accom- 
modation of the Eye." 

Lapsus (lap'-sus). The dropping of the upper lid. 
produced by a paralysis of the levator palpebra 
muscle. Synonym, Ptosis. 

Lashes. The name given to the hairs of the eye- 


Latent (la'-tent). (L. latere = to be concealed.) 
That which is not apparent or manifest. See 

Layer. A stratum having a certain amount of 
thickness and serving the purpose of a covering. 

Leber's Disease (La'-berz). (Theodor Leber, Ger- 
man Ophthalmologist, 1840.) Atrophy of the 
optic nerve, which is hereditary. 

Lema (le'-ma). The dry, hard, yellowish Incrusta- 
tions which collect in the inner canthus. 

Lens. (L. "a lentil.") The term lens was first 
applied to any transparent refracting body 
which had two spherical surfaces, on account 
of its resemblance to a vegetable known as a 
lentil. A lens is a transparent substance, crown 
or flint glass chiefly, ground with regular curva- 
ture on one or both of its opposite sides, but not 
parallel to each other, through which an object 
may appear to be increased or decreased in size, 
and may have either convex or concave spher- 
ical or cylindrical surfaces. There are six vari- 
eties of spherical lenses — three plus and three 
minus — all of which can be made the same diop- 
tric power, the only difference being in the 
shape of the lens. Plus or positive lenses are 
thickest in the center. Minus or negative lenses 
are thinnest at their centers. A plus sphere will 
refract the same in all its meridians and con- 
verge parallel rays of light to a point of focus, 
while a minus sphere will diverge parallel rays 
from a point. The different forms of plus and 
minus spherical lenses are here represented: 

A line passing through the optical center at 
right angles to the surfaces of these lenses is 



not refracted, and is known as the principal 
axis, while all other rays undergo more or less 
refraction. A secondary axis is any line which 

A. Piano Convex. 

B. Biconvex. 

C. Periscopic Convex. 

D. Piano Concave. 

K. Biconcave. 

F. Pei'iscopic Concave. 

crosses the principal axis at the optical center 
of a lens. It is not a straight line, but a re- 
fracted one, and on emerging takes a direction 
parallel to that which it would have pursued 
had it not been interrupted by the lens. Achro- 
matic L., a lens composed of two pieces, one of 
crown and the other of flint glass; the former 
one being plus and the latter minus, and only 
half as strong in its refractive power, but of 
equal dispersive power, and overcomes chro- 
matic aberration. Aplanatic L. is on the order of 
the achromatic lens, except that the minus is 
divided and placed half on each side of the plus. 
In this way not only the chromatic but the 
spherical aberration is overcome, and a perfect 
lens formed. They are used for high-power in- 
struments. Bifocal L. (see Bifocal.) Composite 
L., a lens having three features, namely, spher- 
ical, cylindrical, and prismatic. Cylindrical L.. 
a lens with refractive power in all meridians 


but one. This one is known as the axis, and is 
nothing more than piano glass. The refraction 
varies from zero at the axis to the full strength, 
which is at right angles to the axis. Crossed L., 
a double-convex lens with one radius equal to 
six times the other. Crystalline L., the lens of 
the eye which resembles a crystal. A trans- 
parent double-convex lens situated in its capsule 
behind the pupil, between the aqueous and vit- 
reous humor, and when in a state of rest has a 
focal strength of from plus 19 to plus 20 diop- 
tries. Compound L., a lens consisting of two or 
more lenses made up together, such as a sphere 
and a cylinder. Torlc L., a lens with power in 
all meridians, but of different amounts on the 
same side, usually made extra deep periscopic. 
Fresnel L., a compound lens formed by placing 
around a central convex lens, rings of glass so 
curved as to have the same focus; used, espe- 
cially In light houses, for concentrating light in 
a particular direction. Lenticular L. is a lens 
which is piano at the edges, and the power is 
ground in a space of about half an inch in 
diameter in the center. When a plus lens is 
required it is made in the form of a scale and 
cemented on a piano or simple cylinder. In this 
way we do away with the thick edge of a high- 
power minus lens, and it also makes up in a 
thinner form for a high-power plus, but they 
are never made up in weak lenses. Orthoscopic 
L., a lens with two elements, a sphere and a 
prism, so arranged that the amount of accom- 
modation and convergence used should exactly 
correspond. Periscopic L., a lens having a con- 
vex and concave surface. Ret'roscopic L., a lens 
that is tilted inward at the top. {ovKn> 

Toric Lenses. The word toric was taken from 
the word torus, which means in architecture the 
large semicircular molding used in the bases of 
columns, and the term is applied to a lens hav- 
ing curvature in all meridians, but of different 
amounts, on the same side of the lens with its 
meridians of greatest and least curvature at 
right angles to each other. The meridian of 
least curvature is known as the base curve, 
while the other side of the lens will be piano, a 
concave or a convex sphere; but usually made 

To give an idea of the appearance and proper 
uses of such lenses, I will put up a prescription 
for one of the five subdivisions of ametropia 
which can be corrected by lenses in toric form. 
This can best be explained by diagrams. 

This prescription will be for compound hyper- 
opic astigmatism + 3. sph. ^ + 2. cyl. ax. 90. 





This lens when ground must refract plus 
three dioptries in the ninetieth and plus five 
dioptries in the one hundred and eightieth me- 
ridians, independent of its shape. 

But in order to get a deep periscopic effect, 
the advantage of which 1 will explain later, sup- 
pose we grind one side of the lens thus: 





The difference between the curvatures in the 
two meridians gives us the desired value of the 
cylinder, and on the other side we will grind a 
minus three sphere, which will neutralize plus 
three from all meridians, leaving the lens with 
the required strength. In this lens you get a 
plus sphere and a plus cylinder, and at the same 
time, if a cement scale is required, it can be 
placed next to the eye. 

When a toric lens is desired, it is not neces- 
sary for the refractionist to mention the curva- 
ture. For the sake of simplicity, just write the 
word "toric" beneath the description of the 
lenses in your prescription. Then write the pre- 
scription in the usual way. 

Toric lenses are more expensive than the old 
form of lenses, but on account of their superior- 
ity they are coming more into general use. 

In the first place, they allow a greatly en- 
larged field of vision, by allowing the patient to 
roll the eye and at the same time see through 
the edges of his lens. 

With lenses of the ordinary type, when an 
eye turns it looks obliquely through them and 
obtains a prismatic effect that is not desired, 
causing the image to be more or less distorted 
on the retina, and at the same time the patient 



is bothered with reflection from the back of the 
lenses of objects on the side. With deep peri- 
scopic lenses the curve coincides approximately 
with the arc formed by the eye in turning, and 

the eye is looking much more directly through 
the lens and obtains a much larger field of 
vision without the extra prismatic effect. 

The diagrams show the shape of the two 
kinds of lenses from the same prescription, 
+ 2 sph. C — 1 cyl. ax. 90. 

Again, the edges of the lenses come nearer to 
the face, thus adding to the patient's appear- 
ance. The result of a lens of this description is 
freedom and comfort to the wearer, so much so 
that the extra cost should not be considered. 

When a cement bifocal is required, the toric 
side should always be plus, so that a minus 
sphere will be next to the eye. on which the 
scale may be cemented. 
Lens Capsule (L. a lentile + dim. of capsa = box). 
A transparent, highly elastic, and brittle mem- 
brane which encloses the crystalline lens. It 
rests in a depression of the vitreous body just 
behind the iris, and is held in position by the 
suspensory ligaments. 
Lentlconus den-tik-o'-nus). (L lens -}- conus = 



cone.) Exaggerated curvature of the crystalline 

Lenticular (L. lenticula = a lentlle). Resembling 
a lentil. Lens-shaped; pertaining to a lens. 

Lenticular Astigmatism. See Astigmatism. 

Lesion (le'-shun). (L. loedere = to injure.) Any 
hurt, wound, or local degeneration. 

Leucoma (lew-ko'-mah). See Leukoma. 

Leukoma (lew-ko'-ma). (Gr. leukos = white.) 
White corneal opacity. Albugo. 

Levator (L. levare = to lift). Elevator; a muscle 
raising a part. 

Levator Palpebra Muscle (le-va'-tor pal'-pe-bra 
mus'-l). See Muscles. 

Ligament (lig'-a-ment). (L. ligare = to bind.) A 
tough band of connective tissue, the purpose of 
which is to connect the bones together or sur- 
round them as a capsule. There are several liga- 
ments concerned in the anatomy of the eye. 
Check Ligament, Ciliary Ligament, Palpebral 
Ligament, External Palpebral Ligament, Inter- 
nal Palpebral Ligament, Lockwood Ligament, 
Suspensory Ligament or Zone of Zinn, Liga- 
ment of Zinn. The Ciliary L., or circle (annulus 
albidus), is the bond of union between the ex- 
ternal and middle tunics of the eyeball, and 
serves to connect the cornea and sclerotic, at 
their line of junction, with the iris and external 
layer of the choroid. It is also the point to 
which the ciliary nerves and vessels proceed 
previously to their distribution, and it receives 
the anterior ciliary arteries through ^he anterior 
margin of the sclerotic. A minute vasculd^r 


canal is situated within the ciliary ligament, 
called the ciliary canal, or the Canal of Fontana. 
from its discoverer. Check L., the fibrous bands 
attached by one end to the anterior wall of the 
orbit and by the other to the tendons of the 
recti muscles. Those on the inner side are 
called the internal check ligaments, and those 
on the outer or temple side the external check 
ligaments. The action of these ligaments is a 
normal one. They prevent or retard overaction 
of the abductors or adductors. Lockwood L., 
a band of orbital tissue in the anterior part of 
the orbit, where it forms a hammock-like band 
attached at one end to the lachrimal and at the 
other to the majar bone. Its broader central 
part passes below the eyeball over the Capsule 
of Tenon. The Palpebral L. joins the cartilage 
of the lids to the orbit the same as the tarsal 
ligament. The Externa! Palpebral L. unites the 
lid to the outer edges of the orbit. The Internal 
Palpebral L. covers an area including the upper 
maxilla to the inner margin of the lid. The 
Suspensory L., or Zone of Zinn, surrounds the 
crystalline lens and holds it in place within the 
circle of the muscle of accommodation. 

Ligament of Zinn. A circular ligament which is 
attached to the bone at the optic foramen, from 
which arise the four recti muscles. 

Ligamentum Pectinatum. The ligaments which 
pass from the base of the iris to the cornea. 
Through its meshes pass Fontana's spaces. 

Light (L. lux = light"). Light is that physical 
force which, after entering the eye and acting 
upon the sensitive elements of the retina, ex- 


cites in the mind the impression of vision (or 
vibrations of ether). It is an extremely rare, 
elastic medium which is diffused over the uni- 
verse, emanating from the sun and stars, bodies 
in a state of ignition, candle flame, electricity, 
etc. It is said to travel at the velocity of 
186,000 miles per second while in air. Its speed 
is retarded when it enters a denser medium, as 
water, glass, etc. The amount of the retarda- 
tion depends on the density of the medium. It 
regains its former speed on emerging into air 
again. The unit of light is 1 candlepower. 

Bodies sending forth rays or waves of light 
are called luminous; and those through which 
it passes easily, transparent; those through 
which it can pass less easily, translucent; and 
those through which it cannot pass, opaque. 
When light meets the surface of a body it may 
be reflected, absorbed, refracted, or diffracted. 

It is the cause of color of all bodies, being 
entirely reflected by white objects and absorbed 
by black. It is decomposed in passing through 
a prism, and its seven primary colors exposed, 
thus : violet, indigo, blue, green, yellow, orange, 
and red. Of these, violet is refracted the most 
and red the least. 

Rays of light that do not enter the eye are 
invisible. A ray entering a darkened room is 
visible because the floating dust reflects some 
of it to the eye. 

White light is the combination of all colors, — 
color is not a property of matter, but of light, — • 
for instance, the color of a flower is its property 
of reflecting to the eye light of that particular 
color, the other colored rays being absorbed. 
This is what is known as selective absorption. 


Different colored light has different wave 
length. Red has the longest and violet the 
shortest waves. It will be noted that violet 
must travel much faster than red in order to 
travel with it through space. The main primary 
colors are red, yellow and blue; the others, 
orange, green, indigo and violet, -are secondary 
or "binary" colors. 

In moving colored objects so that their image 
moves from the macula to the periphery of the 
retina, colors grow dim; green is lost first, then 
red, yellow and blue last. Color blindness is 
generally congenital, but may be acquired by 
changes in the retina, particularly in atrophy 
of the optic nerve. 

From an optical standpoint there are two 
theories of the way in which light travels, 
namely, rays and waves. 

A Ray is the smallest visible line of light. 

A Beam is a collection or bundle of parallel 

A Pencil is a number of converging or diverg- 
ing rays. 

Rays emanating from an illuminating or an 
illuminated point always diverge; in nature 
there are no converging rays, neither are there 
any absolutely parallel, but those proceeding 
from a point 20 feet or farther away are so 
nearly so that the difference can only be mathe- 
matically expressed, and for the purposes of 
optics are considered as parallel. According to 
the calculations of astronomers, light moves at 
the rate of about 186,000 miles in a second; 
according to this, it requires about nine minutes 
for the waves of light from the sun to reach the 


earth, and those from the nearest fixed star are 
five years on their journey before tliey reach us. 

From an optical standpoint we now refer to 
the "Wave Theory," and in order to do this it 
will be necessary to draw somewhat on one's 
imagination. You have ofttimes noticed when 
a stone is dropped into a calm pond of water 
it throws forth circular waves in all directions. 
The first or nearest wave to the stone will have 
the shortest radius of curvature, or, in other 
words, the greatest strength of curvature. As 
this wave spreads it will decrease in curvature 
until it has traveled 20 feet. Beyond 20 feet the 
waves are considered plane, meaning by this 
that, when on account of the pupil of the eye 
being about an eighth of an inch in diameter, 
we cut from a wave of light that has traveled 
20 feet a piece one-eighth of an inch long, that 
is, the amount that would enter the eye, it 
would have so slight a curve that it is consid- 
ered to have none. This is known as a plane 

The word minus denotes less; the farther the 
wave travels from its center, the less its curva- 
ture; therefore all waves that are going from a 
point we consider minus, and for the sake of 
simplicity we must compare the waves of light 
with the waves of water, and instead of drop- 
ping the stone we will light a candle that will 
throw off waves in all directions. When a wave 
has traveled one-half inch from a point it has 
a curve of minus 80, because it has a radius of 
curvature of one-eightieth meter. Now, as the 
one and same wave moves on, it loses its curva- 
ture; thus, when it has traveled one inch from 


its center its curvature is less, or minus 40; 
and at two inches, minus 20; three inches, 
minus 13; four inches, minus 10; five inches, 
minus 8; twenty inches, minus 2; forty inches, 
minus 1; eighty inclies, minus .50 (these figures 
are the fractional part of a meter, which the 
distance represents) ; twenty feet, no curve, or 
plane wave. Now, if one will stop to think, he 
will observe these figures compare with the 
focal length of lenses in the trial case; that 
is to say, a wave that has traveled forty inches 
from a point is known as a minus 1, and a 
1-dioptry lens has a focal length of forty inches. 
A wave that has traveled twenty inches from a 
point is known as a minus 2, while a 2-dioptry 
lens would focus at twenty inches. For in- 
stance, you may ask yourself, "What would be 
the curvature of a wave of light that has a 
radius of thirteen inches?" You would at once 
think of the dioptric number of the lens that 
would focus at thirteen inches. This would be 
a 3-dioptry. Then you would say that the curve 
is minus 3, if it is going from a point, but if 
going to a point, plus 3. You will notice that 
in referring to a meter it is spoken of as forty 
inches. There is a difference between the two, 
yet it is near enough for our purpose, and saves 
the trouble and inconvenience of working with 
fractions; so far, we have spoken of the minus 
wave, as all waves in nature are minus; in 
order to have a plus wave we must use arti- 
ficial means, and will work out the following 
example: Place a lighted candle forty inches 
from a plus 3 sphere; considering the candle 
the point from which the light comes; the wave 


has traveled from a point forty inches before it 
enters the lens, therefore it enters a minus 1 
wave. Minus and plus neutralize. If more plus 
than minus is present there will remain, after 
neutralization, an amount of plus equivalent to 
the difference. Therefore the minus 1 will go 
through the plus 3 sphere,- and will emerge a 
plus 2 wave, and focus at twenty inches; at the 
focus they will cross and begin to diverge, or 
rather become minus. 

Light travels at the rate of 186,000 miles in a 
second while in air, but in passing through a 
denser medium, such as glass, its speed is re- 
tarded according to the density, and it regains 
its former speed on emerging into air. 

It always depends on how far a wave is from 
its center of curvature what amount of curve it 
will have. Study the following examples: 



r! is " C > -^ 

Bj ci5 " 

-; ^© o-'-' bE ' ^ 

CO C' ' OS ^ <U 3 
iZ I' ^'^ e i- s* 

. , !=> r- X > — , 

^ 02 a ■>-' 



i ••" =c c g « 

:;; <D (B Ci 


-j^i 0) to O O !« 4) S 

^ '^ n, ^ C -^ --n (O 
o — S rt t- •- 

c3 .5 ^ ^ oj 

m Jl-=! 0) " "l^i ^ W) 

> ^ S m s ;i 5 

^ft3^c«CS5.^ • 
c« t«, :F -: '-^ 






4-4, Cutoptry MiiTor. 


Light, Recomposition of. The reuniting of tlie 
colors of the spectrum so as to produce white 
light. It is done by placing a second prism 
exactly like the first, with its apex turned in the 
opposite direction. The light will be recom- 
posed and will emerge from the second prism as 
white light. 

Light Area on the Face. The term used to desig- 
nate the light upon the face when the bear.i of 
light from the retinoscope is directed upon the 
eye under observation. 

Light Area in Pupil. The light seen in the pupil 
of an eye under observation with the retino- 
scope, caused by the reflex from the retina. Its 
character and relative movement indicate the 
refractive condition of the eye. 

Limbus (L. border). Edge; border; hem. 

Limbus Cornea (lim'-bus). (Border line.) The re- 
gion where the cornea and sclerotic join. 

Limit Angle. See Critical Angle. 

Limitans (lim'-it-ans). (L. limitare = to limit.) 
That which limits or bounds a body or organ. 

Line of Fixation. A line which connects the ob- 
ject looked at with the macula lutea through 
the nodal point of the eye. 

Line of Vision. The line which connects the object 
looked at with the fovea centralis (visual axis). 

Lippitudo (lip-pi-tu'-do). (L. lippus = blear-eyed.) 
An inflammation of the margins of the eyelids. 

Liquor Morgagni. A small quantity of fluid be- 
tween the lens and its capsule. 

Logadectomy (log-ad-ek'-to-my). A removal of a 
part of the conjunctiva by means of a sharp 

Logades (log'-ad-ees). (Gr. logades ^= the whites 
of the eyes.) The first coat or tunic of the eye. 

Logarithm (log'-a-rithm). (Gr. logos = word + 
arithmos = number.) The exponent of the 
power to which a number called the base (in 
the common system, 10) must be raised to pro- 
duce a number 

Loimophtharmia. Contagious ophthalmia. 

Longitude (lon'-ji-tud). (L. longus = long.) The 
angle at the pole between two meridians, one of 
which, the Prime Meridian, passes through some 
conventional point and from which the angle is 

Long-Sightedness. See Hyperopia. 

Lorgnette (lorn-yef). Double eye-glasses attached 
to a handle. This term is often applied to 

Louchettes. A kind of opaque glasses in which, 
for each eye, there is a small opening which 
makes it impossible to look in any other way 
than through this opening. 

Loxophthalmos (lok-sof'-thal-mus). (Gr. loxos = 
slanting -j- ophthalmos = eye.) That condition 
in which the eye is turned from parallelism. 
(Strabismus; Heterotropia.) 

Lucid (L. lucere =^ to shine). Clear, distinct. 

Lucifugal (lu-sif'-u-gal). That condition which 
exists where a person avoids bright light. 

Luminous Bodies. Those sources of direct light, 
as the sun, a lighted candle, etc. 

Luminous Pupil. The appearance of the pupil 

under observation with the retinoscope. 
Luxation fluk sa'-shun) of Lens (L. luxare = to 


dislocate). That condition where the crystalline 
lens is dislocated. 

Lymph (L. lympha = water). A transparent, 
slightly yellow liquid which fills the lymphatic 
vessels. It is occasionally rose color from the 
presence of blood corpuscles, and is often 
opalescent from particles of fat. L. System is 
a collective term for the lymphatic glands and 

Lymphatic (lim-fat'-ik). Pertaining to, of the 
nature of, containing, or conveying lymph. 


.ACRGPSIA (mak-rop'-si-ah). (Gr. makros = 
large + opsis = vision.) That condition of an 
eye in which objects appear larger than they 
really are. 

Macroscopic (mak-ro-scop'-ic). Gr. makros = 
large + skopeo = I view.) That which may be 
seen with the naked eye. 

Macula Lutea (mak'-yu-lah lew'-te-ah). (L. a spot 
+ lutea = yellow.) The small yellow spot of 
the retina which lies directly in the visual axis. 
It is about 4 mm. to the temporal side of the 
center of the optic disc, on the horizontal me- 
ridian, and is less than 2 mm. in diameter. A 
depression in its center, fovea centralis, is the 
most sensitive point of vision. 

Madarosis (mad-ar-o'-sis). (Gr. "bald.") That 
condition in which the eyelashes are perma- 
nently destroyed. 

Maddox Rod (Ernest E. Maddox, English ophthal- 
mologist). An opaque disc with a slit through 
the center. Over this slit is placed a glass rod 

JJJ^ \ \ AkJ X \_/\_^XVJJj ± 

or cylinder. In looking through this rod at a 
small round light it causes the light to look like 

Mafldox Rod. 

a long streak. This rod with a red glass disc 
over the other eye is used for testiLg muscular 
imbalance. Before testing for muscular imbal- 
ance correct all errors of refraction. 

Madisterium (mad-is-ter'-i-um). An instrument 
used for removing the eyelashes. 

Magnet Operation. A method used for removing 
particles of iron and steel embedded within the 
tissue of the eye, by means of a magnet. 

Magnify (mag'-ni-fy). To render an apparent in- 
crease in the size of an object above that seen 
in emmetropia. 

Malacia (mal-a'-se-ah). (Gr. malakia = a soft- 
ness.) Morbid softening of tissue. 

Malacocataracta (mal-ak-o-kat-ar-ak'-tah). A soft 
cataract which forms in the crystalline lens of 
a person under the fortieth year. This form of 
cataract is usually the result of injury. 


Malaxation (mal-ax-a'-shiin). (L. malaxare =to 
sofren.) A rubbing or kneading of the eyeball. 

Malignant (mal-ig'-nant). (L. malus = evil.) 
"Destructive, to cause distress." A term ap- 
plied to any disease whose symptoms are such 
as to threaten the destruction of the part. See 

Malingerer (Fr. malingre = sickly). One who pre- 
tends to have a defect of vision or some other 
function, to evade duty. 

Marginal Keratitis (mar'-jin-al ker-at-i'-tis). (L. 
margo = a border.) Relating to a border or 
edge. A disease of an inflammatory nature 
which occurs usually in elderly people. The 
inflammation extends around the rim of the 
cornea. If the process continues the cornea is 
invaded by a densely vascular, superficially 
ulcerated, and yet thickened zone. 

Marmarygea (mar-mar'-ij-e-a). (Gr. "brilliant.") 
Appearance of sparks before the eyes. 

Mass. (Physics) The quantity of matter which a 
body contains, irrespective of its bulk or volume. 

Mature fma-tur'). (L. maturare = to ripen.) 
Fully developed; ripe. 

Means (menz). The second and third terms of a 

Measure (mezh'-ur). (L. mensura = measure.) A 
unit or standard adopted to determine the 
length, volume, or other quantity of some other 

Media (L. medius = middle). Intervening bodies, 
such as glass, air, water, etc., which light can 
pass through freely. Media is plural of medium. 

Median line, ii. A line perpendicular to and bi- 
secting the distance between the centers of 
rotation of the eyes. 

Medium. Intervening body or quantity. The 
dioptric media of the eye consist of the cornea, I 
aqueous humor, crystalline lens, and vitreous 

Megalocornea (meg-al-o-kor'-ne-ah). fGr. mcgas 
== large.) That condition in which there is 
bulging of the cornea. 

Megalopia (meg-al-o'-pi-ah). (Gr. raegas ^ great 
+ ops = eye.) See Macropsia. 

Megalopsia (meg-al-op'-si-ah). (Gr. megas = great 
+ opsis = vision.) That condition of the eye in 
which objects appear larger than they really 

Meg'aloscope (Gr. megas = great + skopeo = I 
view). A large magnifying lens. 

Megascope (meg'-a-skope). A microscope for ex- 
amining large objects. 

Megophthalmus (meg-of-thal'-mus). (Gr. megas = 
great + ophthalmos = eye.) That condition in 
which the part of eye is abnormally large. 

Meibomian Glands (mi-bo'-me-an; after Meibo- 
mius, the discoverer). A variety of glands 
which are embedded in the tarsal cartilages. 
There are from thirty to forty in the upper lid 
and from twenty to thirty in the lower lid. 
Their ducts open upon the free margin of the 
lids. These glands secrete a sebaceous, oily 
fluid which assists in lubricating the lids as 
they glide over the eyeball, and also prevents 
the lids from sticking together when we have 
them closed. Another function is. that as the 



margins of the lids are kept oily at all times the 
tears do not flow over them so easily. This oily 
substance also mixes with the tears and assists 


To. 1. Meibomian Glands. No. 5. Orbicularis Muscles. 

No. 2. Puncta Lachrymalia. No. 6. Lachrymal Glands. 
Nos. 3 and 4. Lachrymal Canals. 

in preventing friction between the eyeball and 
lids, and at the same time prevents the cornea 
from becoming dry so quickly. Also known as 
tarsal glands. See Chalazion. 

f MeTanin (Gr. melas = black). A dark pigment 
from choroid, hair, and other dark tissues. 

^Melasma (Gr. melas = black). Melanoderma; 
morbid cutaneous discoloration. 

I Melasma Palpebrarum (mel-as'-ma pal-pe-bra'- 
rum). A discoloration of the eyelid, which 
occurs frequently in pregnant women. 

'Membrana Capsularis. That portion of the ar- 
teria centralis which forms a vascular network 
and coats the posterior surface of the lens. 



Membrana Pupillaris (mem-bra'-na). A membrane 
covering the pupil of fetal life. This some- 
times fails to disappear up to time of birth. 

Membrane (mem'-bran). A thin tissue covering 
some surface or organ. 

Membrane Nictitating (L. nictitare = to wink). 
That which is sometimes called the third eye- 
lid, to be seen in various animals. 

Meniscus (men-is'-kus). (Gr. meniskos = cres- 
cent.) A crescent. When applied to a lens, 
would mean that it is more periscopic than 
necessary to produce the same refracting power. 

Menotyphlosis (men-o-tyf-lo'-sis). A condition of 
the eye in which there is diminution of vision 
during night. 

Mensuration (men-su-ra'-shun). The science of 

Meramaurosis (mer-am-au-ro'-sis). A condition of 
the eye in which part of the field of vision is 
lost; partial amaurosis. 

Meridian (mer-id'-i-an). In optics, any straight 
line passing from edge to edge on the surface 
of a lens and over its optical center. A merid- 
ian of the cornea is any straight line crossing 
its surface through its anterior pole. A circle 
describes 360°, one-half of which, or 180°, iS: 
marked on the trial frame. and 180 are found 
in the horizontal, 90° describes the vertical. 
On the clock-dial (astigmatic chart) they are 
numbered from left to right, which must be 
remembered when fitting glasses, and on trial 
frame from right to left. These figures on trial 
frame correspond with clock-dial when they 
face each other. 


Meropia (mer-o'-pi-ah). (Gr. part, vision.) See 

Mesoropter (mes-o-rop'-ter). The position of eyes 

in state of absolute rest. 
Mesoseme (mes'-o-sem). (Gr. mesos = middle + 

sema = sign.) Having a medium orbital index 

between 84 and 89. 

Mesoretina (mes-o-ret'-in-a). (Gr. mesos = mid- 
dle.) The middle layer of the retina. 

Metamorphopsia (met-am-or-fop'-si-ah). (Gr. meta 
= over + morphe = shape + opsis = vision.) 
That condition of the eye in which objects 
appear distorted. 

Metastasis (met-as'-ta-sis). The shifting of the 
seat of a disease from one part of the body to 

Meter (me'-ter). (Gr. metron = measure.) Unit 
of length in the metric system; the equivalent 
of 39.371 inches. 

Meter Angle. The angle through which each eye 
turns when it abandons parallelism of the bi- 
nocular lines (orthophoria) of fixation in order 
to fix an object situated upon the median line 
one meter from the eye. It is the arc embraced 
between the median line and the line of fixa- 
tion, whose length is one meter. The average 
distance between pupils in the adult is 62 mm.; 
then one-meter angle equals a deviation for one 
eye of 31 mm. As the eyes converge closer the 
meter angles increase in proportion. This de- 
scription refers to perfect muscular balance 
only. The writer differs from other authors, 
inasmuch as he claims that if the eyes were 
diverging one meter angle from parallelism, 


when in a state of rest, they will be forced to 
use two meter angles of convergence in order 
to view an object one meter distant. This de- 
scription applies to the different varieties of 
muscular imbalance. 

Meter Lens. A lens that will focus parallel rays 
of light at a distance of one meter. 

Metric Curve. A curve that has a radius of one 
meter; two M, C. has a radius of 20 inches. 

Metric System. A decimal system of weights and 
measures adopted in France (1795) and various 
European countries, and gradually coming into 
general use for scientific purposes. Ten units 
of one denomination marking one unit of the 
next higher. A m.eter is equivalent to about 
39.37 English inches. 

Decimal parts of the standard or principal 
unit are denoted by Latin prefixes; multiples of 
the same, by Greek prefixes. 

From the Latin From the Greek 

Milli means 0.001 Myria means 10,000 

Centi means 0.01 Kilo means 1,000 

Deci means 0.1 Hekto means 100 

Deka means 1 

In the tables units in common use are in bold- 
faced type. 

Units of Length 

Standard unit, the Meter 


10 millimeters (mm.) = 1 centimeter (cm.) 
10 centimeters = 1 decimeter (dm.) 

10 decimeters = 1 meter (m.) 

OPHTHALMIC Dictionary i:.5 

10 meters = 1 dekameter (Dm.) 

10 dekameters =1 hektometfer (Hm.) 

10 hektometers = 1 kilometer (Km.) 

10 kilometers =1 myriameter (Mm.) 

Microblepharia (mi-ki-o-blef-a'-ri-ah). (Gr. mikro^ 
= small + blepharon = eyelid.) A very narrow 
and thin eyelid. 

Microcornia (mi-ki'o-k5t''-iie-ali)* (Gr. mikros =^ 
small.) A small coriiea. 

Microlentia (mi-kro-len'-ti-ah)i A very small crys- 
talline lens. 

Micrometer (Gr. mikros == stiiall + metron =' 
measure). An instrument which is used for 
making measurements of very small bodies. 

Microphtlialmia (my-krof-thal'-mee-ah). (Gr. mi- 
kros = small + ophthalmos = eye.) Abnormally 
small eyes. 

Micropsia (my-krop'-see-ah). (Gr. mikres ^^ 
small + opsis = sight.) That condition of th^ 
eye in which objects appear smaller than they 
really should. 

Microscope (mi'-kro-scope). (Gr. mikros = small 
+ skopeo = I view.) An optical instrument 
used for examining minute objects. 

Migraine (mi-gran')- (Gr. hemi = half 4- kranion 
= skull.) A kind of sickness or nervous head- 
ache, usually periodical and confined to the side 
of the head. 

Mikron (mi'-kron). (Gr. mikros = small). Mil- 
lionth part of a meter. 

Milium (L. millet = seed). A small elevation, on 
the skin of the eyelid, filled with a greasy 

Milphae (mil'-phae). A morbid condition in which 
clie eyelashes drop out. . 

Milphosis (mil-fo'-sis). That condition in which 
the eyebrows as well as the eyelashes have 
fallen out. 

Minify (min'-i-fy). To render an apparent de- 
crease in the size of an object from that seen in 

Minuend (min'-u-end). (L. minuere = to lessen.) 
The number from which another num.ber is 

Minus (mi'-nus). Less: that from which some- 
thing has been subtracted; negative; as,, a 
minus quantity. Minus lenses, same as con- 

Miosis (mi-o'-sis). (Gr. meiosis = a lessening.) 
Excessive contraction of the pupil. 

Miotic (mi-ot'-ic). Any agent or medicine which 
causes the pupil to contract. 

Molecule fmol'-e-kul). The smallest particle of 
any substance. 

Molluscum (mol-us'-kum). (L. mollis ^ soft.) A 
skin disease with pulpy tumors, chiefly on the 
face, neck, and trunk, due to altered gland 
secretion. A small pearly, warty elevation 
which breaks down in the center and discharges 
a cheeselike material. It is said to be con- 

Momentum (mo-men'-tum). (L. momentum = mo- 
tion.) The quantity of motion in a moving 
body, being always proportioned to the quantity 
of matter multiplied into the velocity. 

Monoblepsis (mon-o-blep'-sis). (Gr. monos = one 
+ blepsis = sight.) That condition in which 


objects are seen distinctly only when the eyes 
are used singly, vision being imperfect when 
both eyes are used. 

Monochromatic Light (Gr. monos ^ single + 
chroma = color). The spectrum is formed by 
a prism dividing light into its seven colors. 
Such light is called Monochromatic Light. 

Monocle (mon'-o-kl). An eyeglass to be worn 

over one eye only. 
Monocular (mon-ok'-u-lar). (Gr. monos == single 

+ L. oculus = eye.) Having one eye only. 

Monocular vision is that condition where the 

patient has vision in one eye only. 
Monoculus. A monster with one eye only. 
Moon-Blindness. Amblyopia caused by having the 

eyes exposed to the full ^lare of the moon for 

considerable time. 
Monoparesis (mon-o-par'-es-is). (Gr. monos =^ 

single + paresis.) Paralysis of a single part of 

the body. 
Monopathy (mon-op'-ath-e). (Gr. monos = single 

+ pathos = suffering.) A local disease of one 

organ or function. 
Monops (mon'-ops). (Gr. monos = single -f ops 

-= eye.) A foetus with but one eye. 
Motor (L. "a mover"). A nerve center controlling 

motion. A muscle causing motion. 
Motor Muscles. The muscles that control the 

movements of, or parts of, the eyes — the recti, 

the oblique muscles, the ciliary, and the iris 

Mucocele (mu'-ko-sele). (L. mucus + Gr. kele =^ 

tumor.) Distention of the lachrymal sac, chronic 

thickening of the lining membrane, and in- 
creased secretion of mucus. The mucus may be 
clear or turbid. Any tumor containing mucus. 

jVIuscae Volitantes (mus^-cae vol-i-tan'-tes). (L. 
"flying flies.") Small floating bodies, resem- 
bling sticks, etc., which move about in the field 
of vision, but do not actually cross the fixation 
point, and never interfere with sight. They are 
usually seen against some bright object. They 
depend upon ipinjite changes in the vitreous, 
which are present in nearly ^11 eyes. They 
vary, or seem to vary, greatly with the health 
and state of the circulation, but are of no real 
importance. They are most abundant and 
troublesome in myopic eyes. 

Muscle (L. musculys =: a little mouse, from the 
resemblance of a muscle in contraction to the 
movements of a mouse under a cloth). Muscles. 
(Eye) The eyeball is rotated around its center 
of rotation by the individual pr combined action 
of six muscles, namely, four recti or straight, 
and the two oblique; the seventh muscle, leva- 
tor palpebrae, is attached jtp the upper lid, 
which it raises. 

Of the six muscles inserted into the eyeball, 
five take their origin from the apex of the 
orbit, while the sixth and shortest, the inferior 
oblique, takes its origin from the superior max- 
illary bone at the anterior and nasal side of the 

Internal Rectus Muscle turns tjie eye in, ^nd 
is supplied by the third cranial or motor oculi 

Superior Rectus Muscle turns the eye up, and 


is supplied by the third cranial or motor oculi 

Inferior Rectus Muscle turns the eye down, 
and is supplied by the third cranial or motor 
oculi nerve. 

Inferior Oblique Muscle rolls the eye on its 
optic axis, drawing the bottom and back part of 
the eye in and down while the front moves up 
and out, and is supplied by the third cranial or 
motor oculi nerve. 

External Rectus Muscle turns the eye out, 
and is supplied by the sixth cranial or abducens 

Superior Oblique Muscle rolls the eye on its 
optic axis, turning the back part of the eye 
inward and upward while the front part moves 
down and out, and is supplied by the fourth 
cranial or patheticus nerve. 

Ciliary Muscles are inside the eyeballs, and 
are used for accommodating only. They are 
supplied by the third nerve. 

Orbicularis Palpebrarum Muscle closes the 
lids, and is supplied by the seventh, or facial 
nerve. (One of the muscles of expression.) 

Levator Palpebra Superioris lifts the lids, and 
is fed by a branch of the third cranial nerve. 

Sphincter Muscle, which closes the pupil, is 
supplied by the third nerve. 

Radiating Muscles of the iris, which dilate 
the pupil, are supplied by the sympathetic 

Horner's Muscle. See Tensor Tarsi. 

Palpebral Muscles are two involuntary mus- 
fles, superior and inferior. The superior is 
principally inserted into the upper margin of 

the tarsal plate. The inferior, found in the 
lower lid, interwoven with the fasciculi of the 
orbicularis palpebrarum. 

Riolan's Muscle is the muscular tissue sur- 
rounding the hair follicles and glands of Moll, 
near the border of the eyelids. 


Tensor Tarsi compresses the lachrymal sac 
and pulls the puncta against the eyeball. Sup- 
plied by the seventh cranial nerve. 

Corrugator Supercilii draws eyeorow down 



and inward, and is supplied by the seventh 
facial nerve. 

Cut showing the Extrinsic Muscle. 

Fyramidalis nasi. This muscle depresses the 
eyebrow. Supplied by the seventh facial nerve. 

MuHer's Muscle. Bands of circular fibers sit- 
uated internal to the radiating muscles in the 
ciliary body. They are sometimes called the 
"ring muscle" of Muller. Fibers of Mullen are 
the radiating fibers which pass through nearly 
the entire thickness of the retina, supporting its 
different layers and binding them together. 
They form at one end the membrana limitans 
interna and at the other end the externa. 

Muscular Asthenopia. See Asthenopia. 

Muscular Imbalance. It is generally agreed by 
the authorities of today that ametropia is re- 
sponsible for 90 per cent of Muscular Imbalance. 
For this reason it is considered advisable to 
always correct any ametropia that may be pres- 
ent, and have the patient wear the correction 
for at least six weeks. At the end of this time, 
should any muscular imbalance be manifest, 
correct half of the amount. Always test for 
muscle trouble while the patient is wearing his 
full correction for the ametropia, otherwise it 
will not be considered a proper test. There are 
but few exceptions to this rule: e. g., when a 
prism, base in, will allow you to decrease a 
minus lens or increase a plus, prescribe it. See 
Heterophoria and Heterotropia. 

Mycophthalmla (mi-kof-thaK-mi-ah). Inflamma- 
tion of the conjunctiva, caused by a spongy 

Mydriasis (mid-ri'-as-is). Dilatation of the pupil, 
caused by the use of atropine or other mydriat- 
ics, or paralysis of the motor oculi nerve. 

tVlydriatic (mid-ri-at'-ic). A drug that dilates the 


Myiocephalon (my-i-o-sef'-al-on). (Gr. myia == fly -;- 
kephale = head.) A small protrusion of the iris 
through a perforation of the cornea. 

Myitis (mi-i'-tis). (Gr. mys = muscle -|- itis = in- 
flammation.) Inflammation of the muscles. 

Myodesopsia (Gr. myia = fly -|- opsis = sight). See 
Muscae Volitantes. 

Myograph (ray'-o-graph). (Gr. mys = muscle + 
grapho = I register.) An instrument for record- 
ing the different phases, such as the velocity, 
intensity, etc., of a muscular contraction, with 
the aid of a registering apparatus. 

Myography (my-og'-ra-phy). (Gr. mys = muscle + 
graphe = a drawing.) A description of muscles, 
including the study of muscular contraction, 
with the aid of a registering apparatus. 

Myology (my-ol'-o-ji). (Gr. mys = muscle -|- logia 
= a discourse.) A description of the muscles 
of the human body. 

Myologist (my-ol'-o-gist). One skilled in that part 
of anatomy which treats of muscles. 

Myope (my'-ope). A near-sighted person. 

Myopia (my-o'-pi-ah). (Gr. myo = close -f- ops = 
eye.) An optical defect of the eye which causes 
parallel rays of light to focus in front of the 
retina, with the muscles of accommodation at 
rest. It is also known as Brachymetropia and 
Hypometropia. A correction (concave lens) is 
necessary before normal vision can be obtained. 
In the early days the Greeks noticed that all 
near-sighted persons could see better at a dis- 
tance by half closing the eyelids (squinting). 
hence the name myopia. The eyeball may 

be too long (axial) or the refraction too great, 
causing the parallel rays to cross and meet the 
retina as divergent rays, which form a circle of 
diffusion, and so cause a blurred and indistinct 
image of the object. Myopia from excess of 
curvature is much rarer than the axial form. 
We sometimes see a case of apparent myopia 
due to excess of curvature of the lens, caused 
by a spasm of the ciliary muscle. This is what 
is known as false myopia, and will disappear 
under the iuiluence of atropine, or rest. 

These cuts have not been made with mathematical pre- 
cision, but are merely intended to roughly exemplify the 
principle involved. The above Mlustratts the effect of a 
distant point upon a myopic eye. It will be observed that 
the rays from the distant point cause the image from that 
point to spread out over a considerable area on the retina. 
A million points would make a million blurred spots. 
They would overlap each other and render the picture 

Bonders pronounced every highly myopic eye 
a diseased eye, but of late years it has been 
shown that this remark is liable to convey a 
false meaning. It is admitted that up to 3-D. 
the cases are seldom serious, it being generally 
possible to give perfect vision by proper glasses, 
but when the case is above 5-D. we do not 
always obtain perfect vision by proper lenses, 
and look for vari'^us patholcgical conditions. 


Symptoms: The patient sees distant objects 
badly and near objects better. The pupils are 
usually large, and as presbyopia advances they 
contract. The ciliary muscles are smaller and 
weaker than in the normal or emmetropic eye. 
As a rule, myopic patients cannot wear their 
full correction when first fitted, but after wear- 
ing about two-thirds of the correction for about 
six weeks the full amount may be prescribed. 
Myopia that is gradually on the increase is 
called Progressive Myopia. Myopia that is of a 
rapidly progressive type, and is very destructive 
to the tissues of the eye, is called Malignant 

Myopic Crescent. As seen by the ophthalmoscope. 
is a white crescent at the outer side of the optic 
disc. This condition is caused by the choroid 
being torn away from the optic disc and allow- 
ing the sclerotic to show through. Found in 
high degrees of myopia. 

Myosis (my-o'-sis). (Gr. myo = I close the eye.) 
Abnormal contraction of the pupil. (Same a^ 

Myositis (my'-o-si'-tis). (Gr. mys = muscle + itis 
= inflammation.) Inflammation of the muscles. 

Myotic. (Gr. myo = I close the eye.) An agent 
that will contract the pupil, such as eserin, 
pilocarpine, etc. 

Myotomy (mi-ot'-o-me). (Gr. my s = muscle -f- 
tome = a cutting.) The dissection or division of 


ASAL DUCT (L. nasus = nose -f ducere = to 
lead). That part of the tear duct which extends 
from the lower part of the lacrimal sac to the in- 
ferior canal of the nose. It is about five-eighths 
of an inch in length and lined with a mucous 
membrane similar to the lacrimal canals. At 
the end of the duct we find the valve of Hasner. 

Near Point (or Punctum Proximum). The nearest 
point at which the eye can see distinctly when 
employing its full amount of accommodation. 
It varies with the amount of accommodation the 
eye possesses. The way to determine the near 
point is to note the shortest distance at which 
an emmetrope can read small print with each 
eye separately. Properly speaking, the near 
point is that point for which the eyes' refrac- 
tion is adjusted when the full amount of accom- 
modation is being used. 

Near-Sight. See Myopia. 

Neb'uia (L, "cloud"). Slight corneal opacity. 

Needling (need'-ling). An operation for soft cata- 
ract. The lens capsule is needled, and the 
aqueous allowed to absorb the lens. 

Negative (neg'-a-tive). (L. negare = to deny.) 
The opposite of positive. The negative surface 
of a periscopic lens is the concave surface. 

Neonatus (ne-on-a'-tus). (Gr. neos = new + L, na- 
tus = born.) Newly born. 

Neotocophthalmia (ne-ot-ok-of-thar-mi-ah). See 
Ophthalmia Neonatorum. 

Nephablepsia (nef-ab-lep'-si-ah). See Snow- 


Nepheiopia (nef-el-o'-pi-ah^. (Gr. nephele = cloud 
+ ops ■=^ eye.) A diminution of vision, caused 
by a cloudiness of the transparent parts of the 

Nephritic Retinitis (nee-frit'-ik). A form of in- 
flammation of the retina associated with Brights 
disease of the kidneys, characterized by white 
streaks along the course of the blood-vessels. 

Nerve CL. nervus =^ nerve). A white string-like 
fiber which transmits impressions from an organ 
to the brain or from the brain to an organ. 
Cranial N., any nerve arising from the brain 
direct. There are twelve cranial nerves, as 
follows : 

1. Olfactory, special sense of smell. 

2. Optic, special sense of sight (retina). 

3. Motor Oculi, motor nerve for eye muscles. 

4. Patheticus, motor nerve for superior ob- 
lique muscle. 

5. Trigeminus, sensory, motion, and taste. 

6. Abducens, motor nerve for external rectus 

7. Facial, motor nerve for muscles of face. 

8. Auditory, special sense of hearing. 

9. Glosso-Pharyngeal, sensation and taste. 

10. Pneumogastric, sensation and motion. 

11. Spinal Accessory, motion. 

12. Hypoglossal, motor nerve of tongue. 

The nervous system is a system of connection 
and communication by which the different or- 
gans, vessels, and various parts of the body are 
brought into direct relation with each other and 
with the mind, and the various organs stimu- 
lated to harmonious or alternating action. It. 

consists of the brain and spinal cord, called the 
central nervous system, which controls the vol- 
untary actions of the body, sometimes called 
the nerves of animal life, and is directly con- 
nected with the sympathetic nerves, which have 
been termed nerves of organic life, they being- 
involuntary nerves and control the involuntary 
action of the various vital processes of the 
body. The nervous system is divided into the 
cerebro-spinal or central, sympathetic, and the 
vaso motor. The vaso motor system is a part 
of the sympathetic system and consists of the 
vaso motor center located in the medulla ob- 
longata; of certain other subsidiary vaso motor 
centers in the spinal cord, and of vaso motor 
nerves. This system is connected with the 
blood-vessels in the various parts of the body, 
the muscular coats of which are supplied with 
filaments and plexuses of vaso motor nerves 
which regulate the size of the blood-vessels. 
They are of two kinds: vaso dilators, stimula- 
tion of which causes dilatation of the blood- 
vessels and an increased amount of blood to a 
part, and vaso constrictors, stimulation of which 
causes constriction or contraction of the blood- 
vessels and a diminished amount of blood to a 
part. This last named system is very important 
to the practitioners of manipulatory forms of 
healing, and has only in the past few years 
been known to any extent, the vaso motor cen- 
ter being discovered by Schiff in 1855, and more 
accurately localized by Ludwig in 1871. The 
cranial nerves are those that have their appar- 
ent origin in the cranium. Sommering and 
other European anatomists name twelve pairs, 


while Willis and a few other authors designate 
only nine pairs, according to the order in which 
they pass out of the base of the brain. 

Motor N., one which contains wholly motor 
fibers. N. Center, a group of cells which con- 
sist of gray matter and have a common func- 
tion. Mixed N., a nerve which is both motor 
and sensory. N. Head, the optic disc or papilla. 
Sensory N., any nerve which transmits sensa- 
tions or impulses. Sympathetic N., any nerve 
of the sympathetic system. 

Optic Nerve. The nerve which transmits ret- 
inal sensations from within the eye' to the brain, 
and is known as the second cranial pair. 

The Nerve of Vision. It is about 5 cm. in 
length and may be spoken of in three ways — 
the intracranial, the intraorbital, and the intra- 

The optic nerves are noticeable for their size 
and their running a longer course within the 
cranium than within the orbit, and that they 
furnish no branches from their origin to their 

Transverse sections of the optic nerve show 
it to be composed of about eight hundred dis- 
tinct bundles of nerve fibers, separated from 
each other by connective tissue from the pia 
mater. The entire number of fibers contained 
within the optic nerve probably approaches a 
half million. These fibers after entering through 
the lamina cribrosa (sieve-like opening) again 
pass through the choroidal fissure (hole in cho- 
roid) and spread out in such a way as to form 
the shape of a wineglass (the retina) The 
fibers thems-elves are not rensitive to light, but 

each one terminates in a sensitive point (rods 
and cones) and in all parts of the third tunic 
(the retina), except at ihe entrance of the optic 
nerve (optic disc). See Retina: Optic Tract. 

IIKAD UF Tlii. '^'r: 


D. Ophihiilmoscopic view of the Optir Disc. The sniiiH 
excavations seen around the cM-nter is the Lamina 
• 'riljroHa. The I'apilla Is encir«l»il by th<" white ScKral 
HIiiK (<•» also the dark Choroidal HInK niarke«l (d) 

i;. KonK'tudlnal S« ttlon of H« a»l of Dptif N«Tve ; r, tl»<* 
Iteiiiia; b. (Jptic I0x(avatl«>n and Canal for Central 
Art<ry (porous optlrust; rh. the fliorold; E. Opil< 
Nerve; e. Ihe narrow Interspace whic li lorrespondn t 
the Sidrral HlnR »ei n by the Op)itliahuoscope; s. Scb 
rotir: I I, Entrance of short Ciliary Artery. 

Neurasthenia (nu-ras-thon-i'-ah). (Gr. neuron — 
nerve I astheneia weakness.) Exhaustion of 
nerve force. 


tt « 

orill'HAl.AIh ' I )H'l 1( •XAKV 


Neuritis (iieu ri'-tis). (dr. lU'uron nerve f itis 
iiitlaininatioiij Intlanimatioii of the optic 

Neurology ( nu rol'-o-je). (CJr. neuron uerve -f 

loiAJa discourse.) A study ol the nervous 



1 Eyj'biiM with part of e.xternal rectus muscle. li. 
Superior Maxilla. 3. Thlril pair (or Motor Ocull) nerve.s. 
Th.y art- di.strlbutt-d to all the mu.sclts of the eye. except 
the Supirior obiiijue. External Rectu.s and the Dilator 
.Mu.sili-s of the Iri.s. 4. Fourth pair of Nerves, feeding 
Superior oblique Muscle.s. (J. Sixth pair of Nerves, feed- 
iiiK External Rfctu.-s. 8. t'lllary Nerves entering the globe. 

Neurcdealgia. T'ain or excessive sensibility of 
the retina. 

Neurodeatrophia. Atrophy of the retina. 

Neuroretinitis ( neu-ro-ret-in-i'-tis). ((Jr. neuron =^ 
nerve 4- L. retina -f- Gr. itis.) Intlannnation of 
tlie optic nerve and retina. 

Neutralize (^neu'-tral-ize). (L. neuter neither.) 
'! ht> method of counterbalancing or doing away 
with power in lenses. In order to determine 
whether a lens is of plus or minus power, hold 
i; up a few inches from the eye and look at 

some distant object through it, then move the 
lens from side to side and if the object appears 
to move in the opposite direction to the move- 
ment of the lens it is a plus lens. If you wish 
to find its dioptric power, take from your trial 
case a minus lens and put them together and 
again look through them at the object, and 
should the object still move against the move- 
ment of the lenses the minus is not strong 
enough. On the other hand, should the move- 
ment be reversed and now the objects appear 
to move with the lenses the minus is too strong, 
and you must find the minus lens that will 
allow the object to remain stationary. Whatever 
minus lens is required to do this will be of the 
same power as your plus lens; for instance, it 
will require a — 3 sphere to neutralize a + 3 
sphere. When you look at an object through 
a minus lens, and move the lens as explained 
above, the object will appear to move with the 
movement of your lens, and in order to find 
its dioptric power use plus lenses as in the 
previous test until all movement of the object 
looked at has disappeared, and then the minus 
lens will be the same power as your plus. If 
the lens is compound, use the weakest spherical 
lens which neutralizes the motion in one direc- 
tion; this usually gives the spherical surface, 
then use a cylinder to neutralize motion at 
right angles to this. If in order to neutralize 
a given compound lens, + 2 sphere combined 
with -h 1 cylinder, axis 90° is required, then 
the lens being neutralized is a — 2 sphere com- 
bined with — 1 cylinder, axis 90°, etc. 

Nictitation (nik-tit a'-shun). (L. nictitare = to 


wink.) Involuntary convulsive twitching of the 

Night Blindness. See Nyctalopia. 

Niphablepsia (nif-ab-lep'-si-ah). (Gr. nipha = 
snow + ablepsia == blindness.) That condition 
wherein blindness is caused by the glaring 
reflection of sunlight upon the snow. Snow- 

No'dal Points, or Cardinal Points. Are two points 
situated on the optic axis, connecting the cen- 
ters of curvature of the refracting compound 
dioptric system of the eye. The nodal points 
of the eye are so close together that they may 
be considered as one point. 

Nodal Points of a Lens. The two points of 
the principal axis, so situated that every ray 
which, before being refracted, is directed to- 
ward the first of them, seems, after its refrac- 
tion, to come from the second one, and takes a 
direction parallel to that which it had at first. 
These two parallel rays are called lines of 
direction, and act, in the combined system, the 
same part as the line passing through the 
nodal point of a single refracting surface. 

Normal. (L. norma ^= rule.) That which con- 
forms to the natural rule. A straight line drawn 
from any point of a curve or surface so as to 
be perpendicular to the curve or surface at the 
point which it strikes is said to be normal to 
the surface. 

Normal Vision. Vision is said to be normal when 
an eye can read a line on Snellen's Test Type 
from the distance at which it is numbered. 
The smaller the objects that an eye can dis- 

tinguish or the greater the distance at which it 
can distinguish an object of given size, the 
greater is the acuity of vision that it possesses. 
Suppose, for instance, that the eye is just able 
to distinguish the letters in the line marked 50 
on the Snellen's test type from a distance of 
twenty feet, then the vision would be 20/50. 
The vision in this case would not be as good as 
if the line marked 40 had been read from the 
same distance; and in order to have normal 
vision the patient should read the line marked 
20 at twenty feet, with each eye separately, 
then the vision would be known as 20/20. 
Sometimes the patient will read the line 
marked 15 or even 10 from twenty feet. In 
this case the vision is exceptionally acute, and 
is designated as 20/15 or 20/10. 

Normal vision does not indicate that the eye 
is normal, as the patient may be straining to 
bring the vision up to this point, as in Faculta- 
tive Hypermetropia. Again, an emmetropic eye 
does not always have normal vision. 

Notation (no-ta'-shun). (L. notare = to mark.) A 
system of written signs of things and relations 
used in place of common language. 

Nubecula fnu-bek'-u-la). (L. dim of nubes = 
cloud.) Slight cloudiness of the cornea. 

Nuclear fnu'-kle-ar). Pertaining to the center. 
The controlling center of activity. 

Nuclear Cataract. See Cataract. 

Numeration. (L. numerare = to count.) The art 
of reading numbers. 

Numerator (nu'-me-ra-tor). The number, in a 


common fraction, which shows how many parts 
of a unit are taken. 

Nyctalopia (nyk-tal-o'-pi-ah). (Gr. nycto = night 
-f- alaos = obscure -f ops =^ eye.) Night blind- 
ness. A condition where a person does not 
possess normal night vision. 

Nyctotyphlosis (nyk-to-tyf-lo'-sis.) (Gr. nyx = night 
+ typhlosis ^-^ blindness.) State of blindness 
at night time. 

Nystagmus (nys-tag'-mus). (Gr. nystagmos = a 
nodding.) Short, jerking movements of the eye 
which are very rapidly repeated and always 
occur in the same direction. The movements 
of the eye, as a whole, are not affected by it. 
Defective vision of such cases is not to be at- 
tributed to the nystagmus, but, on the con- 
trary, is the cause of it. Vertical n., the eyes 
continually move vertically. Lateral n., the eyes 
constantly move horizontally. Rotary n., the 
eyes constantly rotate. 

BFUSCATIGN (ob-fus-ka'-shun). (L. ob = to- 
ward + fuscus = dark.) An obscuration of vision 
or a confusion of sight. 

Object. Something visible or tangible. That 
which is seen. An external something the 
image of which is upon the retina, which is in- 
telligently impressed and appreciated by the 

Objective (ob-jek'-tive). (L. ob =^ against 4-Jacere 
-^ to cast.) Symptoms observed by operator 
usually with ophthalmoscope or retinoscope. 
Symptoms which the refractionist discovers by 

means of one or more of his five senses. Ob- 
jective Examination. An examination conducted 
independent of the patient's statements; e. g., 
retinoscopy, ophthalmoscopy and many other 
tests by means of instruments. 

Oblique. Slanting; placed in a plane between the 
horizontal and vertical planes. 

Occipital (ok-sip'-it-al). Pertaining to the back 
part of head. Occipital lobe is the posterior 
portion of the cerebral hemisphere. 

Occipito-Frontalis. The muscle which lifts the 

eyebrows upward. Supplied by the seventh 

Occlusion of the Pupil (ok-klew'-shun). Blocking 

up of the pupil by a membrane. 
Ocellus (o-sel'-lus). (L. "the eye.") A single aye. 
Ocular (ok'-u-lar). (L. oculus = eye.) That which 

pertains to the eye. 

Ocular Refraction. The science treating of the 
optical conditions of the eye, the estimation of 
its errors of refraction and their connection 
with lenses for the eye. 

Ocular Spectres. Imaginary objects floating be- 
fore the eyes. 

Oculist (ok'-u-list). (L. oculus ^ eye.) A physi- 
cian and surgeon who has received the degree, 
"Doctor of Medicine," and makes a specialty of 
the eye and its diseases. 

Oculo-Motor Center is a point situated beneath 
the floor of the aqueduct of Silvius around 
w^hich the impulse to u?8 accommodation united 
with the action to use the different muscles of 
the eye is stimulated. 


Oculomotor (ok'-yu-loh-moh'-tor). (L. oculus = 
eye + motus — motion.) Pertaining to the 
movements of the eye. 

Oculus (ok'-yii-his). The organ of vision. 

O. D. Oculus Dexter. The right eye. 

Offset Guard. An eye-glass guard with a long 
shank, the purpose of which is to hold lenses 
farther from the eyes. 

Old Sight. See Presbyopia. 

O'nyx. (Gr. "nail.") An accumulation of pus be- 
tween the layers of the cornea, resembling a 
finger nail. 

Opacity (o-pas'-i-ty). (L. opacus = obscure.) The 
quality of that which is opaque. 

Opaque (o-pake'). Impervious to light. Not trans- 

Operculum. (L. "lid," cover.) Anything resem- 
bling a lid or cover. 

Operculum Oculi (o-per-cu'-lum oc'-u-li). The eye- 

Operation (op-er-a'-shun). (L. opus = work.) Ajj 
act performed with instruments or by the hands 
of a surgeon. 

Ophryitis (of-ry-i'-tis). (Gr. ophrys = eyebrow + 
itis = inflammation.) That condition in which 
the eyebrows are inflamed. 

Ophrys fof'-rys). (Gr. eyebrow.) 

Ophthalmagra (of-thal'-ma-grah). (Gr. ophthal- 
mos eye -}- agra ^ seizure.) A sudden intense 
pain in the eye. usually rheumatic or gouty in 

Ophthalmalgia fof-thal-mar-ge-ah ). (Gr. ophthal- 
mos = eye -j- algos ^ pain.) Sudden violent 
pain in the eye, not the result of inflammation, 
but neuralgic in character. 

Ophthalmatrophia (of-thal-mah-tro'-fe-ah). (Gr. 
ophthalmos = eye + atrophia =^ atrophy.) Atro- 
phy of the eye. 

Ophthalmia (of-thal'-mi-ah). Severe inflammation 
of the eye. This more particularly applies to 
the conjunctiva of the eyelids and eyeball. 

OphthaI'mia Neonato'rum. (Gr. ophthalmos =■ 
eye + L. neonatus --= new-born.) A form of 
purulent conjunctivitis which attacks newly 
born children. 

Ophthalmic (of-thal'-mic). That which pertains 

to the eye. Ophthalmic Lens, a lens to be 

worn before the eye. 
Ophthalmitic (of-thal-mit'-ic). That which applies 

to inflammatory diseases of the deeper as well 

as the superficial structures of the eye. 
Ophthalmitis (of-thal-mi'-tis). (Gr. ophthalmos = 

eye + itis.) Inflammation of the eye, more 
• especially the globe with its membranes. 
Ophthalmoblennorrhoea (blen-ur-ree'-ah). (Gr. 

ophthalmos = eye + blenna =^ mucus + rhoia = 

flow.) A flow of mucus from the eye. 
Ophthalmocarcinoma (kahr-si-no'-mah). Cancer 

of the eye. 
Ophthalmocele. (Gr. ophthalmos ^ eye -\- kele == 

hernia.) See Stapyloma. ' - 

Ophthalmocopia (koh'-pee-ah). (Gr. ophthalmos 

= eye + kopos =^ fatigue.) Fatigue of the eyes; | 



Ophthalmodynia ( -iliir-e-ah ). (Gr. ophthalmos 
eye -r odyne - pain.) Neuralgic pain of the 

Ophthalmography (mog'-rha-fee). (Gr. ophthal- 
mos eye ->- graphe a description.) A de- 
scription of the eye. 

Ophthalmologist (of-thal-mol'-o-gist). One who 
practices ophthalmology and has taken the de- 
gree. "Doctor of Medicine." An Oculist. 

Ophthalmology (of-thal-mol'-o-gy). A study of the 
eye and its diseases. 

Ophthalmomacrosis f-ma-kro'-sis). Enlargement 

of the eyeballs. 

Ophthalmomalacia (-ma-la'-sha). (Gr. ophthalmos 

— eye -+- malakia = softness.) That condition 
in which there is abnormal softness of the eye- 

Ophthalmopathy (mop'-a-thee). (Gr. ophthalmos 

— eye + pathos ^ suffering.) Any disease of 
the eye. 

Ophthalmophthisis (-mof'-thi-sis). (Gr. ophthal- 
mos eye — phthisis wasting.) That condi- 
tion in which there is wasting of the eyeballs. 

Ophthalmoplegia (-ple'-je-ah). (Gr. ophthalmos — 
eye f plege stroke.) Paralysis of the ocular 
muscles of the eye. O. Partial, a form in which 
only some of the muscles are paralyzed. O. 
Progressive, a gradual paralysis of all the mus 
cles ot both eyes. O. Total, when the iris and 
ciliary body, as well as the external muscles, 
are paralyzed. O. Externa, when the external 
muscles are paralyzed. O. Interna, paralvsis of 
the internal muscles. 

Ophthalmoptoma (-mop-to'-mah). Protrusion of 

the eyeballs. 

Ophthalmoptosia (-mop-to'-sia). (Gr. opht.halmos 
= eye + ptosis ^= a falling.) Protrusion of the 

Ophthalmorrhagia (-mor-rha'-gee-ah). (Gr. oph- 
thalmos = eye + rhegnymi = I burst forth.) 
Hemorrhage from the eye or orbit. 

Ophthalmorrhexis (-mor-rex'-is). (Gr. ophthalmos' 
= eye + rhexis = rupture.) The bursting of 
the eyeball. 

Ophthalmoscope (of-thal '-mo-scope). (Gr. oph- 
thalmos = eye -j- skopeo = I examine.) An in- 
strument for observing the interior of the eye. 
and thus determining the appearance of the 
media, the condition of the retina, choroid and 
optic nerve, and the state of the refraction. 

The Ophthalmoscope consists of a round 
mirror, with a small perforation in the center. 
The surface of the mirror is usually concave. 
The more improved ophthalmoscopes have a 
reversible mirror, one side of which is flat and 
the other concave. In addition to this there are 
located on the back of the ophthalmoscope 
several wheels which contain a great variety of 
convex and concave lenses. By rotating these 
wheels the different lenses contained in them 
can be thrown immediately behind the aper- 
ture in the mirror. 

There are two methods of examining the eyes 
with the ophthalmoscope, viz.: the indirect and 
the direct. 

The indirect method is not of much value so 
far as estimating the refraction of the eye is 




concerned, but gives a good view of the fundus 
of the eye. enabling us to examine in minute 
detail the optic disc and the blood vessels of 
the retina ; also to observe whether any dis- 
eased condition exists in the interior of the 

To perform this method successfully, we seat 
our patient in the dark room and place a light, 
either an argand gas burner, an electric light, 
or any ordinary kerosene student's lamp, at the 
side and slightly back of the patient's head. If 
we wish to examine the left eye we place the 
light on the left side of the patient's head, and 
if we wish to examine the right eye, on the 
right side. We place the light just far enough 
back of the head to avoid illuminating the pa- 
tient's face. We take our seat in front of the 

patient and hold our ophthalmoscope at the 
focal distance of its mirror, reflect the light 
into the patient's eye, and look through the 
sight hole in our mirror. The next step is to 
place a strong convex lens immediately in 
front of our patient's eye. With our mirror we 
illuminate the retina, and the rays emanating 

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well to place the patient under the influence 
of atropine, assuming that the operator haj^ 
thorough control of his own accommodatiou 
and can suspend it at will. 

By reflecting the light into the Emmetropic 
eye we Illuminate the retina; the retina again 
reflects the light so that it passes through the 
pupil and out of the eye. The rays from eacli 
reflecting point emerge from the eye as parallel 
rays. Therefore, if the operator's eye is Emme- 
tropic he will, by the aid of these rays, be able to 
distinctly see the details of the fundus in the 
back part of his patient's eye, because the 
light leaves the patient's eye as parallel rays, 
and the operator's eye, being also emmetropic, 
is adapted for parallel rays, and hence he has 
each point on the patient's retina represented 
by an exact focus on his own retina. 

It can readily be seen that if a patient has 
used any accommodation the rays would leave 
his eye, not as .parallel, but as convergent rays, 
and therefore the operator would have been 
unable to distinctly see the details of the fun- 
dus. On the other hand, if the patient had been 
under the influence of atropine and the rays 
had left the eye as parallel rays striking the 
observer's emmetropic eye, as parallel rays, 
they would not focus upon the operator's retina 
if he had used any accommodation. Hence the 
necessity of thorough relaxation of accommo- 
dation in both the patient and operator. 

We will next suppose that the hypermetropic 
eye is being examined by an operator who is 
emmetropic. The rays of light will leave the 
hypermetropic eye as divergent rays and there- 



fore will not focus upon the retina of the ob- 
server's emmetropic eye, and hence he will be 
unable to distinctly see the details of the fun- 
dus in the patient's eye. He now rotates the 
wheel on the back of his ophthalmoscope, 
throwing different lenses into the aperture of 
the mirror, until finally he strikes one which 
enables him to distinctly see his patient's 
retina. The glass which produces this result 
will represent the measure of his patient's 

hypermetropia. In order that the operator may 
distinctly see the patient's retina, he must use 
a convex glass strong enough to render parallel 
the divergent rays which are leaving his pa- 
tient's eye. 

In myopia the patient's eye is too long, and 
the rays of light which leave the myopic eye 
will therefore leave as convergent rays and 
focus in front of the observer's retina, so that 
in this case he will also be unable to distinctly 
see the fundus of his patient's eye, and as in 
the case of the hypermetropic eye he rotates 
the wheel on his ophthalmoscope until he is 
able to distinctly see the retina of the myopic 
eye. The glass which accomplishes this result 
is the measure of the patient's myopia. 

In order that he may distinctly see the back 

of this eye, a concave glass must be used strong 
enough to render parallel the convergent rays 
which are leaving the myopic eye. 

It is usually conceded that in astigmatism 
the ophthalmoscope is of little or no value. It 
is true that we may be able to see the blood- 
vessels and the edges of the optic disc clearer 
in one meridian than in another, and that we 
may use a glass strong enough to render plain the 

meridian which was at first blurred, and there- 
by dim the meridian which was first seen 
plainly. The glass which clears up the merid- 
ian which seemed blurred at first would be the 
measure of the ametropia in the meridian at 
right angles to it. 

It must also be remembered that if the operator 
is not emmetropic he must either have his own 
refraction properly corrected by glasses, or he 
must make deductions or additions, as the case 
may be, to or from whatever glass clears up the 
retina in the patient's eye. For instance, if 
the operator knows himself to be hypermetropic 
to the extent of one dioptry. and on examining 
his patient's eye he finds that a plus 3-D. glass 
is required to enable him to see the details of 
his patient's fundus, he then knows that his 
patient has two dioptries of hypermetropia, "be- 


cause one of the three was required to correct 
his own eye. and likewise if he had been exam 
ining a myopic eye and found that a minus 2-D. 
lens was required to see his patient's retina, he 
would know that his patient had three dioptries 
of myopia, because he himself was one dioptry 

Ophthalmoscopy (oph'-thal-mos'-copy). The art of 
judging healthy or diseased conditions of the 
eyes by means of the ophthalmoscope. There 
are two methods of examining the eyes with 
the ophthalmoscope, viz.: the direct and the 

Ophthalmostat (of-thal'-mo-stat). (Gr. ophthal- 
mos =^ eye + statos =^ made to stand.) An eye- 

Ophthalmula (of-thal'-mu-lah). A cicatrix located 
upon the eye or its appendages. 

Optic. (Gr. opsis = vision.) That which pertains 
to the science of light, and also to the eye 
itself, together with its functions. 

Optic Atrophy. A partial or total loss of sight 

due to atrophy of the optic nerve. 
Optic Axis. A line drawn through the center of 

the cornea, through the nodal point to the 

inner side of the macula lutea. In other words, 

through the center of the eyeball from before 

Optic Groove. A transverse groove on the upper 

surface of the sphenoid bone on which the optic 

nerve rests. 
Optic Nueritis. Inflammation of the optic nerve. 
Optical. Pertaining to the organ of vision. 

optical Center. A point where the secondary 
axis crosses the principal axis on line with the 
thickest part of a plus sphere or the thinnest 
part of a minus. A ray of light when passing 
through the optical center of a lens will always 
emerge parallel to the incident ray or in the 
same plane. Optical Center of a Lens. The 
center of refraction. It is found by making two 
parallel radii of curvature, and connecting the 
points in which they meet the surfaces. The 
point at which this line cuts the principal axis, 
is the optical center. 

Optical Corrections. Lenses that change the di- 
rection of light rays entering the eyes to such 
an extent that the eyes are adapted to receive 
and focus them upon the retina, creating artifi- 
cial emmetropic conditions when ametropic con- 
ditions exist. 

Optic Commissure (kom'-mis-ur). The linking or 
joining together of the right and left optic 

Optic Disc. That spot on the retina which marks 
the entrance of the optic nerves into the eye. 
It is also called the blind spot, or papilla. 

Optic Excavation. The depression in the optic 

Optic Nerve. See under nerve. 

Optic Papilla (pap-il'-lah). The elevation of the 
optic-nerve head; also called the optic disc and 
blind spot. 

Optician (op-tish'-an). A person skilled in tlie 
manufacture of optical instruments. 


Optics. That part of the science of physics which 
deals with the transmission of liglit, the laws 
of refraction, reflection and the phenomena of 


Optic Tract. The optic nerve between the visnal 
centers and the optic commissure. 

The Optic Nerve, which, in part, is known as 
the optic tract, is formed by two roots, in ihe 
floor of the brain, the external and the internal 

The External Root has its origin in three gray 
matter centers: (1) The optic thalamus; (2) 
the external geniculate (knee-like) body, and the 
anterior tubercles of the corpora quandrige- 
mina (four bodies). 

The Internal Root arises from two gray mat- 
ter centers; they are the internal geniculate 
body and the posterior tubercles of the corpora 
quadrigemina (four bodies). 

These sight centers which give origin to the 
optic tracts are connected to the cerebral cor- 
tex by a number of fibers known as the cor- 
tico optic radiating fasciculi and form the most 
posterior part of the optic thalamus (bedj. 
These later fibers are supposed to be of a sen- 
sory nature, and to communicate with the dif- 
ferent sections of the brain. The fibers of the 
external and internal roots come together to form 
the optic tract, it passes forward along under 
the posterior of the optic thalamus, crosses the 
crus cerebri, and again crosses the side of the 
tuber cinerium to the optic groove on the 
sphenoid bone where it unites with the optic 
tract of the other side to form the optic com- 
missure. In the optic commissure the fibers of 

each optic tract divide, and the outer fibers of 
each tract are continued into the nerve of the 
same side, while the central fibers of each tract 
continue into the optic nerve of the opposite 
side, crossing each other and passing througli 
the optic foramen to enter the eye. 

The dura mater and pia mater which lines 
the skull passes through the optic foramen 
(hole into orbit) and forms the optic sheath or 
covering of the optic nerve until it enters the 
lamina cribrosa (sieve-like opening of the eye) 
and spreads out to form the retina. 

Optist (op'-tist). A person skilled in optometry. 

Optogram (op'-to-gram). (Gr. optos = visible + 
gramma = a picture.) A faint image stamped 
on the retina for a brief period. 

Optology (op'-tol-o-ge). See Optometry. 

Optometrist. One who measures the eye's refrac- 

Optometry (op-tom'-e-try). (Gr. optikos = be- 
longing to sight -f metron =^ measure.) The 
science and art of employing the various meth- 
ods of measuring the optical state of the eye. 

O'ra Serra'ta (a serrated border). The anterior 
limit or edge of the retina. So named from its 
saw-like appearance. 

Orb. A spherical body. 

Orbicular. (L. orbiculus = a small disc.) Annu- 
lar, circular. 

Orbicularis Palpebrarum. The circular muscle of 
the eyelids. 

Orbiculus Ciliaris. A zone of about one-sixth of 


an in^n in width. It is directly continuous with 
the anterior part of the choroid. 

Orbit (or'-bit). (L. orbita = track). The bony 
socket in which the eyeball is placed. The 
orbits are conical in shape with their apices 
extending backward and toward each other 
while the front or base of the cone is open, 
leaving the eyeballs to be protected by the eye- 
lids in front. 

Anatomy of Orbits. The orbits are two pyra- 
midal cavities 1% inches wide by 1% inches 
deep, situated at the upper and anterior part 
of the face, their bases being directly forward 
and outward and their apices backward and 
inward, so that the axes of the two if continued 
backward Avould meet over the body of the 
sphenoid bone. The orbit is lined with perios- 
teum, the periorbita. Each orbit is formed of 
seven bones, the frontal, the sphenoid, ethmoid, 
superior maxillary, malar, lachrymal and pal- 
ate; but three of these, the frontal, ethmoid and 
sphenoid, enter into the formation of both or- 
bits, so that the two cavities are formed of 
eleven bones only. The orbital opening, or 
mouth, is called aditus orbitae (Aditus Orbitae 
— entrance to orbit). At the apex, or back part 
of the orbit on the nasal side, is a small circu- 
lar opening known as the optic foramen, which 
transmits the optic nerve and ophthalmic 
artery. There are nine openings communi- 
cating with each orbit, viz., the optic foramen, 
the spheno-maxillary fissure, sphenoidal fissure, 
supraorbital foramen, anterior and posterior 

• ethmoidal foramina, infraorbital canal, malai 
foramina, and the canal for the nasal duct. 

Sphenomaxillary fissure transmits the superior 
maxillary nerve and its orbital branches, the 
mfraorbital vessels, and the ascending branches - 
from the spheno-palatine or Meckel's ganglion. 
Sphenoidal fissure transmits the third, the 
fourth, the three branches of the ophthalmic 
division of the fifth, the sixth nerve, some fila- 
ments from the cavernous plexus of the sympa- 
thetic, the orbital branch of the middle menin- 
geal artery, and a branch from the lachrymal 
artery of the dura mater, and the ophthalmic 
vein. Supraorbital foramen transmits the 
supraorbital artery, nerve and vein. Anterior 
ethmoidal foramen transmits the anterior eth- 
moidal vessels and nasal nerve. Posterior eth- 
moidal foramen transmits the posterior eth- 
moidal vessels. Infraorbital canal opens just 
below the margin of the orbit. Malar foramina 
is a passage for nerves and vessels from the 

Orbital (or'-bit-al). Pertaining to the orbit. 

Origin (or'-ij-in). (L. origo = beginning.) The 
more fixed end of a muscle; for instance, the 
end attached to the bone of the orbit. 

Orthochromatic (or-tho-chro-mat'-ic). (Gr. orthos 
= straight -|- chroma = color.) A term used 
by photographers denoting that the colors are 
normal or correct. 

Orthometer (or-thom'-e-ter). (Gr. orthos = straight 
-f- metron = measure.) An instrument for find- 
ing the exact relative protrusion of the two eye- 

Orthoptic (or-thop'-tic) . (Gr. orthos = straight -f 
optikos = relating to sight.) Relating to the 


straightening of a deviating eye by means of 

Orthophoria (or-tho-foh'-ree-ah). (Gr. orthos = 
straight + phoria = tending.) That condition 
in which the eyes, or better, the visual axes, are 
parallel when the extrinsic muscles are in a 
state of rest. Perfect muscular balance. 

Orthoptic (or-thop'-tic). (Gr. orthos = straight -f 
optikos ^ relating to sight.) Correcting hetero- 
phoria, or strabismus, by means of the prism 
exercise. This is accomplished by placing the 
base of the prism over the strong muscle, thus 
causing the weak muscle to contract or draw 
the eye toward the apex of the prism in order 
to see. 

Orthoscope (or'-tho-scoI)e). (Gr. orthos = straight 
-f skopeo =- I view.) An instrument for neu- 
tralizing the refraction of the cornea by exam- 
ining it through water. 

Orthoscopic Lenses. A lens with two elements — 
a sphere and a prism — so arranged that the 
amount of accommodation and convergence 
used should exactly correspond. 

Orthotropia (or-tho-tro'-piah). (Gr. orthos = 

straight + trope =— turn.) Perfect binocular 

V fixation. With this condition heterophoria may 

I exist and some muscle or muscles are under 
strain to hold the eyes parallel, yet it is gen- 
erally accompanied by orthophoria. 
Osseous (os'-e-us). Bony. Resembling bone. 
O. S. (Oculus Sinister). Left eye. 
O. U. (Ovular Unati). Both eyes. 

Oxyopia (ox -y-o'-pi-ah). (Gr. oxys = acute + ops 
= eye.) That condition in which the sight is 
abnormally acute. 

1 ACHYBLEPHARON (pach-y-blef-ar'-on). (Gr. 
pachys = thick + blepharon = eyelid.) That 
condition in which the eyelids have become 

Palpebra (pal'-pe-brah). (L. palpetare = to palpi- 
tate.) The eyelid. Inferior P., lower eyelid. 
Superior P., upper eyelid. Tertia P., third eye- 
lid. See Membrana Nictitians. 

Palpebral (pal'-pe-bral). (Gr. palpebra = eyelid.) 
That which relates to the eyelid. 

Palpebral Fissure fpal'-pe-bral). The space be- 
tween the free margins of the eyelids. The 
outer angle of fissure is called the external can- 
thus; the inner angle, the internal canthus. 
The small- space between the lids and globe at 
inner angle is called the lacus lachrymalis. 

Palpebrltis (pal-pe-bri'-tis). (L. palpebra = eyelid 
4- Gr. itis = inflammation.) An inflammation of 
the eyelids. 

Pannus (pan'-nus). (L. "a piece of cloth.") A 
web-like patch of grayish membranish tissue 
usually covering the upper half of the cornea, 
making it almost opaque. It is usuallv caused 
by the rubbing of roughened or granulated lids 
over the cornea and results in the eifort of 
nature to protect this membrane. 

Panophthalmia (pan-of-thal'-mi-ah). An inflamma- 
tion of the entire eye structure. 


Panophthalmitis ( pan-off -thal-mi'-tis). (Gr. pas 
(pan) = all + ophthalmos = eye.) General in- 
flammation of the eyeball. 

Pantiscopic. A lens tilted outward at the top. 

Pantometer (pan-tom'-e-ter). An instrument for 
measuring angles and determining perpendicu- 

Papilla (pap-il'-lah). (L. "nipple.") A conic ele- 
vation observable at the optic-nerve head. P. 
Lachrymal is, the mound at the inner canthus 
of the eye pierced by the lachrymal puncta. 

Papillitis (pap-il-li'-tis). That condition in which 
tliere is an inflammation of the optic disc or 

Papilloretinitis (pap-il-lo-ret-in-i'-tis). Inflamma- 
tion of the optic disc and retina. 

Parablepsis (par-ab-lep'-sis). (Gr. para ^ beside 
+ blepsis = sight.) False vision, 

Paracente'sis. (Gr. para = beside -f kentesis = 
puncture.) Surgical puncture of a cavity. 

Paracentesis Cornea (-sen-tee'-sis). Puncture of 
the cornea. 

Parallax (par'-al-lax). An apparent displacement 
of an object, due to change in the observer's 
position, or when closing one eye. 

Parallel (par'-al-lel). That which pursues the 

same direction, but in a separate path. 
Parallelepiped (par-a-lel-e-pip'-ed). (Gr. paral- 

lelos = parallel + epipedon = plane.) A prism 

whose bases are parallelograms. 
Parallelogram (par-a-lel'-o-gram). (Gr. parallelos 

=— parallel + gramma = line.) A quadrilateral 

whose opposite sides are parallel. 

Parallelism (par'-al-lel-ism). State of being par- 
allel. That condition in which the visual axes 
of both eyes lie in nearly parallel paths. 

Paral'ysis. (Gr. "I loosen" — "I relax.") That con- 
dition in which there is a loss of power of vol- 
untary motion or of sensation in a part from 
lesion of nerve substance. Oculo-motor P., 
where the motor oculi nerve is affected. 

Paralysis of Accommodation. That condition in 
which the function of the branch of the third 
nerve which supplies the ciliary muscles has 
been interrupted and the eye cannot accommo- 
date, the ciliary muscles being in a state of rest. 

Paralyt'ic. (Gr. affection.) Pertaining to, or 
affected with, paralysis; a person who is 
affected with paralysis. 

Paresis (par'-es-is). (Gr. "a relaxing.'") A slight 
form of paralysis. 

Paropsis (par-op'-sis). (Gr. para ^ beside -^opsis 
= vision.) That condition in which the vision 
is disordered, and may be due to either a false 
impression being made upon the retina or a dis- 
ordered condition of the mind. 

Passive. (L. passivus = to endure.) That which 
is not active; for instance, a muscle that is in a 
state of rest. 

Pathetic (pa-thet'-ik). That which pertains to 
the feelings. The pathetic muscle is the su- 
perior oblique muscle of the eye, which receives 
its name from the fact that the patheticus. or 
fourth pair of cranial nerves, control its move- 

Pathologic. Pertaining to diseased conditions. 


Pathological (path-o-log'-i-cal). See Pathology. 

Pathology fpath-or-o-je). (Gr. pathos = suffering 
-f logis discourse.) The science which has for 
its object the knowledge of disease. 

Pediculis Pubis (ped-ik'-u-lus pu'-bis). (L. "crab- 
louse.") Crab-louse. In very rare cases they 
will reach the eyelashes and flourish there. The 
lice cling close to the border of the lid, and 
look like dirty scabs; the eggs are darker, and 
may also be mistaken for bits of dirt. The ab- 
sence of inflammation and the rather peculiar 
appearance will lead, in doubtful cases, to the 
use of a magnifying glass, by which the ques- 
tion will be settled at once. 

Penumbra (pe-num'-brah). A partial shadow. 

Perception. (L. percipere = to perceive.) The 
acquiring of impression through the senses. 
Centers of sight p., those portions of the brain 
that are the sources of the optic nerves. 

Perceptivity (per-sep-tiv'-it-e). Capacity to re- 
ceive impressions. 

Perfection Bifocal. See Bifocal. 

Perichoroidal (-koh-roy'-dul). That which sur- 
rounds the choroid membrane. 

Pericorneal f per-i-cor'-ne-al). (Gr. peri = around.) 
That which is situated around the cornea. 

Perimeter (per-im'-e-tur). (Gr. peri =^ around -f- 
metron ~-= measure.) An instrument for meas- 
uring the field of vision. 

Perimetry fpe-rim'-et-re). (Gr. perimetros = cir- 
cumference.) Measurement of the visual field. 

Periocular fper-e-ok'-u-lar). (Gr. peri = around -f 
L. oculus - eye.) That which encircles the eye. 

Perioptic. See Periocular. 

Perioptometry (per-e-op-tom'-et-re). (Gr. peri = 
around + optikos = referring to vision — metron 
= measure.) Measurement of the visual acuity 
of the retinal periphery. 

Periorbita rper-i-or'-bit-a). (Gr. peri = around + 
L. orbita = orbit.) That which relates to the 
lining membrane of the orbit. 

Periorbital (per-i-or'-bit-al). Around or about the 

Periorbitis (per-e-or'-bi-tis). Inflammation of the 
lining membrane of the bones of the orbit. 
Orbital periostitis. ^ 

Periosteitis (per-e-os-te-i'-tis). Inflammation of 
the periosteum. 

Periosteum (per-e-os'-te-um). (Gr. peri-=^ around 
-f osteon =bone.) The tough, fibrous mem- 
brane investing a bone. 

Peripheraphose fper-if-er'-af-oz). The subjective 
sensation of a dark spot in a patch of light, the 
cause residing in the eye, optic nerve or out- 
side of optic center in the brain. 

Periphacitis Tper-i-fa-si'-tis). CGr. peri = around 
+ phakos = lens — itis.) Inflammation of the 
crystalline lens of the eye. _ 

Periphacus (per-if-a'-cus). The crystalline lens 

Periphery (per-if'-er-y). (Gr. peri —around -r 
phero = I carry.) Any outward part or sur- 
face; for instance, the border of the cornea or 
crystalline lens. 

Periscopic (per-is-cop'-ic). (Gr. peri = around -}- 
skopeo = I view.) A lens having a concave 


and convex surface. Periscopic lenses are also 
called meniscus lenses; taken from a Greek 
word meaning a crescent. See Lens. 

Peritomy (per-it'-o-me). (Gr. peri = around + 
tome = incision.) An operation for the treat- 
ment of pannus, by removing a strip of the con- 
junctiva around the cornea. 

Perivascular (per-i-vas'-ku-lar). (Gr. peri = around 
+ L. vasculum = vessel.) Surrounding a vessel. 

Perivascuirtis. (Gr. peri = around + L- vasculum 
= vessel + itis.) Inflammation of the sheath 
of a vessel. This is an increase or a hyperplasia 
of the connective tissue about the vessels, prin- 
cipally, and usually, the arteries. 

Perspicilium (per-spic-il'-i-um). An apparatus to 
enable an individual to see minute bodies, or 
which will improve the eyesight. 

Pescorvi'nus. That which is commonly knov^nas 
crow's foot; or wrinkles at the outer corner of 
the eye. 

Petit. Frangois Pourfour du Petit, French sur- 
geon and anatomist, 1664-1741. 

Petit's Canal. The space between the suspensory 
ligaments in which the edge of the crystalline 
lens with its capsule is inserted. 

Phaco (fak'-o). Prefix meaning of, or pertaining 
to, a lens, especially the crystalline lens. 

Phacitis (fas-i'-tis). (Gr. phakos = lens -f Itis.) 
Inflammation of the crystalline lens. 

Phacomalacia (fak-o-mal-a'-she-ah). (Gr. phakos 
= lens + malakia = softness.) A soft cataract. 

Phacometer (fa-com'-e-ter). (Gr. phakos =^ lens -f 
metron = measure.) An instrument for meas- 

iiring the curvature of lenses, and so determin- 
ing their refractive power; if they are cylin- 
drical, will locate their axes. 

Phacosclerosis (fa-ko-scle-ro'-sis). (Gr. phakos = 
lens + sklerosis -^ hardening.) Hardening of 
the crystalline lens. 

Phacoscope (fa'-ko-scope). (Gr. phakos = lens + 
skopeo ^= 1 view.) An instrument used for 
viewing the accommodative changes of the 
crystalline lens. 

Phakitis (fa-ki'-tis). (Gr. phakos — lens + itis.) 
Inflammation of the lens, A supposition exists 
that the crystalline lens may become inflamed. 

Phantasma (fan'-tas-mah). (Gr. phantasma ^ an 
appearance.) A disease of the eye in which 
imaginary objects are seen. 

Phengophobia (fen-go-fo'-bi-ah). (Gr. piiengos = 
daylight -f phobos = fear.) See Photophobia. 

Phimosis (fi-mo'-sis) Constriction. (Gr. "to muz- 
zle.") Abnormal smallness (as of the palpebral 

Pho'rotone. (Gr. phora = motion + tonos ten- 
sion.) An instrument for exercising the mus- 
cles of the eye. 

Phosgenic (fos-jen'-ik). (Gr. phos ^ light + 
gennao =^-- to produce.) Light producing. 

Phlyctenula (flik-ten'-u-lah). ((!r. "blister.") A 
small vesicle or blister. 

Phlysis (fly'-sis). A corneal ulcer. 
Phoria. (Gr. "a tending.") 

Phonometer. An instrument for determining the 
insufliciencies of the external ocular muscles. 



Phorometroscope (phor-o-met'-ro-scope). An in- 
strument for determining the amount, correc- 
tion and treatment of muscular asthenopia by 
gymnastic exercise of the extrinsic muscles. 

Phoroscope. An instrument in the form of a head- 
rest, with a clamp attached so that it may be 
fastened to a table, and is used as a fixed trial 

Phose (foz). (Gr. phos = light.) A subjective 
sensation of light or color. 

Phosphenes (fos'-feenz). (Gr. phos = light -f- 
phaino =^ I show.) A luminous sensation caused 
by pressing on the eyeball. 

Phosphorescence ffos-fo-res'-ens), (Gr. phos =: 
light -r phoros = bearer.) The quality of be- 
coming luminous in the dark without sensible 

Photalgia rto-tal'-je-ah). (Gr. phos = light -f- 
algos = pain.) Pain in the eye arising from 
too much light. 

Photochromatic (fo-to-chro-mat'-ic). TGr. phos = 
light 4- chroma = color.) That which pertains 
to various colored lights. 

Photodysphoria. See photophobia. 

Photogenic. See Phosgenic. 

Photology ffo-tol'-o-gy). The science of light. 

Photometer, (-tom'-e-ter). (Gr. phos = light 4- 
metron = measure.) An instrument for testing 
the light sense. 

Photonosus (fo-ton'-o-sus). TGr. phos = light -f- 
nosos = disease.) Any disease of the eye which 
arises from exposure to the glare of light. 

Photophobia (fo-to-fo'-bi-ah). (Gr. phos = light + 
phobos = fear. ) Intolerance of light. 

Photopsia (fo-top'-si-ah). (Gr. phos = light + 
opsis = vision.) That condition in which one 
sees flashes of light. It is caused either by 
pressure on the eyeballs or by disease of the 
brain, optic nerve, or retina. 

Photoptometer (fo-top-tom'-e-ter). (Gr. phos = 
light 4- optos = visible + metron = measure.) A 
device for measuring sensitiveness to light by 
showing the smallest amount of light that will 
allow an object to become visible. 

Phthisis Buibi (tis'-sis). (Gr. a wasting.) Shrink- 
age of the eyeball. 

Physiolog'icaF. See physiology. 

Physiology (fiz-e-ol'-o-je). (Gr. physis = nature + 
logia = discourse.) That department of nat- 
ural science which treats of the organs of the 
body and their functions. 

Physostigmine (fl-so-stig'-min). The same as 

Pla Mater (L. "tender, affectionate mother"). The 
innermost membrane of the brain and spinal 
cord, optic sheath, and capsule of Tenon. 

Pigment (L. pingere = to paint.) The coloring 
matter in the choroid coat; the iris, etc. 

Pilosebaceous (pi'-lo-se-ba'-ce-ous). (L. pilus =^ 
hair -f sebum = suet.) Relating to the hair 
follicles and sebaceous glands. 

Pinguecula (ping-gwek'-yu-lah). (L. pinguis = 
fat.) A small, yellowish elevation, situated in 
the conjunctiva near the margin of the cornea. 
Found in old age. 

OPHTHALMTP nir-nnNAivi^ 201 

Pinhole Disc. An opaque uisc with a pinhole in 
the center, found in the trial test case. It is 
placed in the trial frame quite close to the eye 
under examination. This perforation gives pas- 
sage to a small pencil of light which passes 
through the center of the refracting media of 
the eye. If the patient can see better through 
the pinhole, the refracting system is at fault, 
and vision can be improved by glasses. If, on 
the contrary, vision is not improved, then we 
suspect a defect in the sensibility of the retina 
or the transparency of the media of the eye. 

Pink Eye. A catarrhal conjunctivitis. The eye- 
ball is of a pink or reddish color. It is a con- 
tagious disease which occurs among cattle and 
horses as well as in man. 

Pladaro'sis (Gr. pladaros = flaccid + oma = tu- 
mor). That condition where there is a soft 
tumor on the eyelid. 

Plane (L. planus = flat). When applied to glass. 
a flat surface is meant. A plano-concave lens 
is a lens having one side concave while the 
other side is flat. A plane disc, or a piano, is 
an accessory found in the trial case which has 
two surfaces, both of which are plane. 

Plastic (plas'-tik). (Gr. plastikos = form.) Tend- 
ing to build up tissues. 

Plexus (plex'-us). (L. plectere = "to weave.") A 
network or interjoining of nerves or vessels. 

Plica (L. plicare = to fold). A fold. Applied to a 
disease in which the hairs become tangled and 
glued together. 

Plica Semilunaris (ply'-kah). A fold of conjunc- 
tiva near inner canthus of the eye. 

Point (L. punctum). The far point or punctum 
remotum is the farthest point at which the eye 
can see clearly and distinctly with the accom- 
modation at rest. The near point or punctum 
proximum is the nearest point at which the eye 
can see clearly with all of its accommodation in 
use. P. of Reversal. In Retinoscopy the term 
is used to designate the point between an erect 
and an inverted image, where the change from 
one to the other occurs. Where convergent rays 
change to divergent rays. The myopic far point 
in retinoscopy is where the movement of the 
reflex appears neutralized. In other words, it 
is that point on one side of which the shadow 
movement is different than on the other. For 
instance, at any position nearer the eye than 
the point of reversal the shadow will move 
against the mirror, and at any position farther 
from the eye the shadow will move with the 
mirror. This refers to the concave retinoscope. 
With the flat mirror the movement would be 
directly opposite. P. of Fixation. The point for 
which accommodation of the eye is adjusted. 

Polarlmeter (L. polaris = polar + Gr. metron =^ 
measure). An instrument for measuring the 
rotation of polarized light. 

Polariscope (L. polaris = polar + skopeo = I ex- 
amine). An instrument used in showing the 
phenomena of the polarization of light. 

Polarization. The production of a condition in 
light by virtue of which all its vibrations take 
place in one plane, or in circles and ellipses. 

Pole (L. polus = poIe). The summit of a spher- 
ical surface. 


Polychromatic (pol-y-chro-mat'-ic). (Gr. polys =^ 
many + chroma = color.) Possessing many 

Polycoria (pol-e-ko'-re-ah). (Gr. polys = many + 
kore = pupil.) The presence of more than one 

Polyopia (pol-e-o'-pe-ah). (Gr. polys = many + 
ops = eye.) Multiple vision. 

Polyoptrum (pol'-y-op'-trum). (Gr. polys = many 
-f optos = seen.) A glass through which ob- 
jects appear multiplied but reduced in size. 

Pop-Eyed. A large protruding condition of the 


Pore (Gr. "passage"). The superficial opening of 
a vessel; one of the small openings existing in 
all bodies. 

Po'rus Opticus (L. porus = pore + Gr. opticus = 
optic). The opening through the lamina crib- 
rosa through which the arteria centralis retina 
and veins pass. 

Positive. That condition which is real and abso- 
lute. The positive surface of a periscopic lens 
is tne convex surface. 

Posterior (L. post = after). Behind; back. 
Postocular (L. post = behind + oculus = eye). 
Posterior to the eyeball. 

Postocular Neuritis (L. post = behind -}- oculus = 
eye + Gr. neuron = nerve + itis). Inflammation 
of part of optic nerve behind the eyeball. 

Presbyopia (pres-by-o'-pi-ah). (Gr. presbys = old 
+ ops = eye.) When as the result of age the 
power of accommodation has diminisli-f^d to such 
an extent that the eye (corrected for distance, 

if ametropic) cannot produce sufficient accom- 
modation for the reading distance, the condi- 
tion is called presbyopia. The average age when 
this state of affairs is present is 45, and as age 
advances the accommodation gradually dimin- 
ishes and the presbyopia correspondingly in- 
creases. The amount of presbyopia is repre- 
sented by the difference between the number of 
dioptries of comfortable accommodation present 
and three dioptries, which must be made good 
by plus spheres. The presbyope sees well at a 
distance, providing there is no error of refrac- 
tion, but has difficulty in maintaining good 
vision for near w^ork, and the eyes become tired 
after reading, especially at night. He has 
trouble in seeing small objects because he has 
to hold them far away, and consequently gets a 
smaller visual angle. Before correcting pres- 
byopia it is necessary to test the patients dis- 
tant vision and correct any error of refraction. 
Then place the reading chart in his hand; if he 
cannot read with comfort at the distance he 
wishes to hold it. add plus spheres of even 
amount in front of his correction until you find 
the weakest that will allow comfort in reading. 
The distance for which the presbyope requires 
glasses will also vary much according to his or 
her occupation; ordinarily it is thirteen inches. 
This gradual failure of accommodation is due 
to hardening of the crystalline lens, loss of 
power of the ciliary muscle, or both. 

Prescription (pre-scrip'-shun). (L. prae = before 
-f scribere = to write.) The formula for the 
lenses required by a patient, which are desig- 


iiated by technical characters placed on blanks 
arranged for this purpose. 

Principal Focus. The focus of parallel rays of 
light on the principal axis after being reflected 
or refracted. 

Principal Meridians. The meridians of greatest 
and least curvature. 

Principal Planes. Straight lines which pass 
through the principal points, perpendicular to 
the principal axis. 

Prism. When applied to optics, is a wedge-shaped, 
transparent body of glass having two plane 
sides, employed for the purpose of bending rays 
of light. A prism is not a lens, and a ray of 
light is always bent towards its base. It is used 
in making tests for muscular insufficiencies, and 
sometimes prescribed for constant wear in cases 
of heterophoria. 

Prisms are numbered by the angle which 
their surfaces incline toward each other; for 
instance, four 90° prisms with their bases and 
apices placed together would form a circle. The 
bending power the prism possesses depends 
upon the difference of density of the glass itself 
and the medium which jt is in. The ordinary 
prism is made of crown glass and deviates a 
ray of light about half of its own value; that is, 
a 4° prism would deviate a ray of light 2°. 

Dennett in his method of measuring prisms 
calls his unit the centrad, which is the hun- 
dredth part of a radian, a radian being the 
angle subtended at the center of a circle by an 
arc, which is equal in length to the radian. 

Prentice Method is the prism dioptry, which 

is any prism that has the power to deflect a ray 
of light 1 cm. for each meter of distance. 

These three methods of numbering prisms 
differ very little for low degrees in ophthal- 

Rotating Prisms. If two prisms of equal 
strength be placed with the base of one over 
the apex of the other, they neutralize each 
other, and if we rotate them in opposite direc- 
tions we obtain the effect of any prismatic de- 
gree up to their combined values. A prism 
forms no image and has no focus, and when 
looked through, the eye turns toward the apex. 
Deaton P., a prism attached to a microscope to 
give the oblique illumination for observing very 
fine markings. Lateral P., an equal-sided, total 
reflecting prism for illuminating a microscopic 

Prism-dicptry, n. In Optics, a standard deflection 
of a beam of parallel rays of light produced by 
a prism. It is equal to 1 cm. on a tangent plane 
placed at a distance of 1 m. behind the prism. 
To practically measure this deflection while 
looking through a prism or lens, and conse- 
quently upon a tangent plane placed in front of 
the prism, it is necessary to multiply these 
dimensions by six, in order to insure parallel 
incidence of the rays constituting the beam of 
light. The prism-dioptry establishes a definite 
relation between the refractive powers of prisms 
and lenses, since "the prism-dioptries in decen- 
tered lenses are in direct proportion to their 
refractive powers and decentraticn (see Decen- 
tration). The prism-dioptry also bears a unique 


relation to the meter angle (see M. Ang.). The 
sign used to designate the prism-dioptry is a 
triangle. Thus the unit, lA of the dioptral sys- 
tem is distinguished from 1° of the old degree 
system. Since 1895 American lens manufac- 
turers have adopted the prism-dioptry as the 
standard unit of prismatic power. 

Prismatic (pris-mat'-ic). That which has the 
shape or effect of a prism. When a lens is 
decentered it will produce a prismatic effect. 

Prlsmoid (priz'-moid). A body that resembles a 
prism in form. 

Prisoptometer (pris-op-tom'-et-er). (Gr. prisma = 
prism + optos = seen + metron = measure.) An 
instrument used for testing the refraction of 
the eye by means of a revolving prism. 

Probe. A long, slender instrument for exploring 
wounds. Lacrimal P. is a probe designed for 
use on the tear passages. 

Problem (prob'-lem). (Gr. problema = a question 
proposed for solution.) 

Product (prod'-ukt). (L. pro = forward -f- ducere 

^^ to lead.) The result from multiplying one 

number by another. 
Progressive Myopia. Myopia that is gradually on 

the increase. 
Prophthalmos (prof-thal'-mos). (L. pro = forward 

-f ophthalmos = eye.) A bulging forward or 

undue prominence of the eyeball. 

Proportion (pro-por'-shun). (L. pro = before + 
portio = share.) A proportion is an expression 
of equality of ratios. 

Proptosis fprop-to'-sis). (Gr. pro = forward -|- 
ptosis = falling.) A falling down or sinking of 
a part. 

Prosthesis (Gr. in addition to + to put). The 
addition of an artificial part to supply that 
which is wanting. 

Prosthesis Ocularis (pro-the'-sis). The insertion 
of an artificial eye. 

Protractor Scale (L. protrahere = to draw forth). 
A device for indicating the location of the axis 
of a cylinder lens. 

Pseudoblepsis (seu-do-blep'-sis). (Gr. pseudes = 
false + blepsis = vision.) That condition in 
which objects look different from what they 
really are. 

Pseudoglioma (seu'-do-gly-oh'-mah). A circum- 
scribed collection of pus in the vitreous. 

Psorophthalmla (soh-rof-thal'-mee-ah). (Gr. pso- 
ros = scabby + ophthalmos = eye.) That in- 
flammatory condition of the eye which is accom- 
panied with itchy ulcerations. 

Pterygium (ter-yg'-i-um). (Gr. pteryx = wing.) 
A thickening or growth of the conjunctiva, 
having the appearance of a fly's wing, usually 
on the nasal side of the eye, extending out 
toward the cornea. It can be removed by opera- 
tion, and should be as soon as it reaches the 
cornea, otherwise it will grow over it and impair 

Pterygoid (ter'-ig-oid). (Gr. pteryx = wing -f- 
eidos = resemblance.) Wing-shaped. 



Ptilosis (ti-lo'-sis). That condition where there is 
a falling out or loss of the eyelashes. 

Ptosis (to'-sis). (Gr. ptosis = a falling.) A droop- 
ing of the upper eyelid. This condition is caused 
by paralysis of that branch of the third or motor 
oculi nerve which supplies the levator palpebra 
muscle. It may also be caused by the thicken- 
ing of the upper lid. 

Puncta fpunc'-tah). CL. punctum = a point.) A 
small prominence or point. See Puncta Lacri- 

Puncta Lacrimalia Cpunc'-ta lak-ri-mal'-i-ah.) (L. 
punctum = point + lachryma = tear.) Two small 
openings near the nasal end of the surface of 
each eyelid, through which the tear passes into 
the lachrymal canal. 

Punctum (punc'-tum). A fixed point. See Punc- 
tum Remotum and Punctum Proximum. 

Punctum Remotum. See Far Point. 

Punctum Proximum. See Near Point. 

Pupil (pupil). (From L. pupa, a babe; so called 
from the small image seen in the eye.) The 
circular opening in the iris through which all 
the rays of light pass that have to form an 
image of the object on the retina. This aper- 
ture is dilated and contracted so as to regulate 
the amount of light entering the eye. The pupil 
of man is round, and by it the anterior and 
posterior chambers of the eye communicate 
with each other. A contracted pupil (myosis) 
indicates inflammation of the brain; a sensitive 
retina, faculative hypermetropia, effect of 

opium or other drugs. A dilated pupil (myd- 
riasis) indicates effect of atropine or other 
drugs, myopia, amblyopia, absolute hypermetro- 
pia, glaucoma, or paralysis of third nerve. 

Anisocoria. Unequal pupils. 

Corectopia. Displacement of the pupil. 

Cored isis. Closure of the pupil by a mem- 
brane, which causes loss of visual acuity. 

Coremorphosis. The operation for artificial 

The shape of the pupil is changed by syne- 
chiae, coloboma, iridodialysis, ruptures of the 
sphincter muscle. The pupil appears black 
when no light returns through it to the eye of 
the observer. It is more dilated in youth than 
in the aged. 

Pupillary (pu'-pil-lar-ry). Pertaining to the pupil. 

Pupillometer (pu-pil-om'-et-er). (L. pupilla = pu- 
pil + Gr. metron = measure.) An instrument 
for measuring the diameter of the pupil. 

Pupllloscopy (L. pupilla = pupil -f- skopeo = I 
view). See Retinoscopy. 

Puplllostatometer (pu-pil-o-stat-om'-et-er). (L. 
« pupilla = pupil + Gr. statos = placed + metron 

= measure.) An instrument to measure the 

distance between pupils. 

Pyrkinges Images. The images seen on surface 
of cornea and lens. See Catoptric Test. 

Pyrometer (py-rom'-e-ter). (Gr. pyr = fire + met- 
ron = measure.) An instrument for measuring 
high degrees of heat. 


l^UADRI LATERAL (kwod-ri-lat'-e-ral). (L. qua- 
tuor — four + latus ^=^ a side.) A four-sided 
plane figure. 

Quantity (liwon'-ti-ti). (L. quantus = how much.) 
Any amount, in measure or extent. 

Quiz CL. quaesitio = inquisition). Instruction by 
questions and answers. Q. Class, a body of stu- 
dents forming a class for the purpose of being 
questioned by a teacher. (See last few pages.) 

Quotient (kwo'-shent). (L. quotiens =: how many 
times.) The number resulting from the division 
of one number by another. 


ACEMOSE (ras'-e-mos). (L. racemus = a 
bunch of grapes.) Bunched; clustered; as in 
staphyloma, where the bulging occurs in several 

Radiad (ra'-de-adl. Towards the radial side. 

Radial (,ra'-de-al). Of or pertaining to the radius. 

Radian. An arc of a circle which is equal to the 
radius, or the angle measured by such an arc. 

Radiant (ra'-de-ant). (L. radiare — to shine.) 
Diverging, as rays from a center. 

Radiation (ra-di-a'-shun). Where rays of light 
appear to be thrown off from a common center. 

Radius (L. "spoke"). The half of the diameter of 
a circle. 

Range of Accommodation. The distance of a pa- 
tient's vision, or the range between the near 
point and the far point of vision. 

Range of Vision. The distance between the near 
and far point. 

Ratio (ra'-sho). (L., from reri, ratus = to reckon.) 
The relation which one quantity or magnitude 
has to another of the same kind. It is expressed 
by the quotient itself, making ratio equivalent 
to a number. The term ratio is also sometimes 
applied to the difference of two quantities as 
well as to their quotient, in which case the 
former is called arithmetical ratio, the latter 
geometrical ratio. Ratio of a geometrical pro- 
gression, the constant quantity by which each 
term is multiplied to produce the one suc- 

Ray. The smallest imaginary line of light. 

Reciprocal Numbers (L, reciprocus = alternating). 
Two numbers which multiplied together make 

Rectangle (rek'-tang-gl). (L. rectus = right + an- 
gulus = angle.) A quadrilateral all of whose 
angles are right angles. 

Rectus (L. straight). Applied especially to cer- 
tain straight muscles. 

Red-Blindness. That condition in which a person 
is unable to distinguish red. 

Reduction (re-duk'-shun). (L. re = back + ducere 
^ to bring.) Changing the denomination of 
numbers. Reduction Ascending, changing to a 
higher denomination, as from 144 inches to 12 
feet. Reduction Descending, changing to a 
lower denomination. 

Reflection fre-flec'-shun), (L. re = back + flee- 
tere = to bend.) Throwing back light. Reflec- 


tion from a plane surface gives an erect imago, 
and the angle of reflection is always equal to 
the angle of incidence. The image is formed at 
a distance behind the reflecting surface equal to 
the (not so with curved mirrors) distance of the 
object in front of it, and is called a virtual 

Reflection by a concave mirror. Parallel rays 
falling on a concave surface are reflected as 
convergent rays which meet at a point called 
the principal focus, which is equal to half the 
radius. The distance of the focus from the 
mirror is called its focal length. 

Reflection from a convex surface. Parallel 
rays falling on a convex surface diverge and 
never meet. No matter what the position of 
the object before a convex mirror, the image is 
always virtual, erect, and smaller than the 
Reflector (re-flec'-tor). A device for reflecting 

Refracting Media (see Media). R. System. A lens, 
or combination of lenses, for the creation of 
optical images. 

Refraction (re-frac'-shun), (L. re = back + fran- 
gere = to break.) The bending of a ray of 
light in passing obliquely from one medium to 
another of different density. This bending is 
caused by one side of the ray having its speed 
increased or decreased according to the density 
of the second medium. Refraction never takes 
place in any one medium, but between the 
media. Light in passing from a rarer to a 
denser medium is bent toward the perpendicu- 
lar, and from a denser to a rarer is bent away 

from the perpendicular. Double R., refraction 
in which the incident ray is divided into two 
refracted rays. Static R., refraction of the eye 


A% It emerges 


No. 1 ray of light is called the incident before entering the 
second medium. A ray passing from a rarer lo a 
denser medium is refracted towards the perpendicular, 
as shown in the above cut. The ray BA is refracted 
on striking the glass MM, and again refracted on 
emerging. In passing from a denser to a rarer me- 
dium, the ray is refracted from the perpendicular. 
P. represents a ray falling perpendicular to the surface 
separating the two media. It continues its course 
without undergoing any refraction. 

No. 2 represents the reflected ray. The angle formed by 
the incident ray with the perpendicular is always equal 
to the angle of reflection. 

The dotted line marked BA' represents the course the 
No. 1 ray would have taken had it not been refracted. 

The side of the incident ray marked B will be found at 
R in the reflected ray, and A at F, 

at rest. Dynamic R., refraction of the eye, plus 
that secured by accommodation. 

Absolute index of Refraction is that which is 


found when light passes from a vacuum into a 
given medium. 

Refraction ist (re-frac'-tion-ist). One who is skilled 
in correcting errors of refraction of the eye. 

Refractive (re-frac'-tive). Pertaining to refraction. 
Refractometer (re-frak-tom'-e-ter). An instrument 
for measuring refraction. 

Regular (reg'-u-lar). (L. regula = a rule,) Accord- 
ing to rule; normal. 

Relative Index of Refraction is that which is 
found when light passes from atmospheric air 
into another medium. 

Relax (L. re = back + laxare = to loosen). To 
loosen, to slacken. 

Relaxa'tion. A lessening of tension. 

Remedy (L. re = again + mederi = to heal). Any- 
thing acting as a cure for, or the relief from, 
unhealthy conditions. 

Reposition (re-po-zi'-shun). (L. repositus = to lay 
up.) The act of putting back in a normal 

Retina (ret'-in-a). (L. rete = a net.) On the inner 
surface of the choroid, and closely in contact 
with it, we find the internal or third and most 
important of the ocular tunics, the retina; to 
which, indeed, the other two are merely protec- 
tive or containing membranes. The retina is the 
immediate continuation of the optic nerve, which 
extends from the brain to the eyeball, perfo- 
rates the sclerotic and choroid, and immediately 
spreads out into a thin lamina over the surface 
of the latter, and is attached at two points only 
— at the entrance of the optic nerve and at its 

most anterior border, the ora serrata. The point 
of entrance of the optic nerve, which is known 
as the optic disc, is nearly on the horizontal 
meridian of the globe, and about one-tenth of 
an inch to the nasal side of the posterior pole, 
so that it is the left eye which is represented in 

a — macula lutea, the most sensitive part of the retina. 

the cut under Anatomy. The function of the 
retina is to receive the pictures which are 
formed within the eye by means of the waves 
of light reflected from objects, and, through the 
medium of the optic nerve, to transmit the 
resulting visual impressions to the brain. 

Just as the sense of touch is not diffused uni- 
formly over the surface of the body, but is more 
acute in some parts — for instance, the finger 
tips — than in others, so also the retina is not 
equally sensitive to the luminous impressions 
over its whole surface, but in the highest de- 
gree a little to the temple side of the posterior 
pole, in a part known as the macula lutea, or 
yellow spot, which may be considered the real 
center of the retina, yet it is to one side. From 
this spot the sensitiveness gradually diminishes 
to its most anterior edge. The retina does not 


extend as far forward as the choroid, but termi- 
nates a little in front of the equator, at the 
posterior border of the ciliary body, in a saw- 
like margin, the rough edge of which is known 
as the era serrata. 

Structures of the Retina According to Gray. 
From within outward, the layers of the retina 
are named as follows: 

1. Membrana limitans interna, 

2. Fibrous layer, consisting of nerve fibers. 

3. Vesicular layer, consisting of nerve cells. 

4. Inner molecular, or granular layer. 

5. Inner nuclear layer. 

6. Outer molecular, or granular layer. 

7. Outer nuclear layer. 

8. Membrana limitans externa. 

9. Layer of rods and cones, or Jacob's Mem- 

10. Pigmentary layer. 
Retinal Reflex. A term used in retinoscopy to 
designate the light reflected from the retina and 
creating the light in the pupil. 

Retinitis (ret-in-i'-tis). (L. retina + Gr , itis = 
inflammation.) Inflammation of the retina. It 
is characterized first of all by a diffused cloudi- 
ness of the organ. The cloudiness varies very 
greatly in intensity, although in general it is 
greatest in the vicinity of the optic disc, because 
here the retina is thickest. Consequently, the 
outlines of the optic disc become indistinct and 
the vessels in the retina hazy. The function of 
the retina is impaired in proportion to the in 
tensity and extent of the inflammation. In the 
lightest cases vision may be normal, so that the 
patients complain simply of the presence of a 

light-colored cloud before their eyes. But for 
the most part vision is very considerably re- 
duced, both because of the changes in the retina 
itself and because of the accompanying opac- 
ities in the vitreous. The course of retinitis is 
always rather sluggish. It is only in the lightest 
cases that the inflammation abates completely 
within a few weeks, and then the visual acuity 
may once more become perfectlj' normal. But 
for the most part it takes several months for all 
the inflammatory symptoms to disappear from 
the retina, while the sight remains permanently 
impaired. Severe and, more particularly, recur- 
rent inflammations of the retina lead to atrophy 
of it, pigmentation frequently occurring at the 
same time (through migration of pigment from 
the pigment-epithelium). When atrophy of the 
retina has once made its appearance, the sight 
is always destroyed, either completely or all 
except a small remnant, and its restoration is 
no longer possible. 

Retinoscope (ret'-in-o-scope). An instrument with 
which an objective examination of the dioptric 
state or condition of the eyes may be measured. 
(Made in plane and concave.) 

The concave can be combined with a strong 
plus lens, about 20-D., and used as an ophthal- 
moscope. There is also a difference in the move- 
ment of the shadow in retinoscopy. In working 
with the plane mirror between 53 and 60 inches, 
the movement is against in myopia of .75 or 
more, while in hypermetropia, emmetropia, or 
less than .75 of myopia the shadow moves with 
the mirror. With the concave it is just the re- 
verse; the shadow in hypermetropia, emmetro- 


pia, and a small amount of myopia will go 
against the mirror. In more than .75 of myopia, 
the movement will be with the mirror. 

It makes no difference which you use. the 
findings will be the same, and you deduct from 
plus and add to minus findings the same 
amounts; it depends on the distance you are 

Hand Retinoseope. 

sitting from the patient. When sitting at a lit- 
tle over 40 inches, you subtract one dioptry from 
all plus findings, and add minus .75 to all minus 
findings. When working between 53 and 60 
inches, you subtract .75 from all plus findings 
and add minus .50 to all minus findings. 
Retinoscopy (ret-in-os'-co-py). (L. retina + scopeo 
=- 1 examine.) "Skiametry." Retinoscopy, or 
the Shadow Test, is one of the methods of esti- 
mating the refraction of the eye. We examine 
the movements of the shadow when the fundus 
is illuminated by light thrown into the eye from 
a mirror. 

With the Concave Mirror. The patient is 
seated in a dark room, with the light placed a 
little above the head, and far enough back so 
that it will throw no direct rays upon his face. 
It is best to use a shade around the light to 
prevent it from illuminating the walls of the 
room, having a hole an inch in diameter in the 

front and about the center of the flame. We 
will now begin with the examination. 

In examining the right eye have the patient 
look across your right shoulder, and in exam- 
ining the left have him look over your left 

Once in a position to begin the test, we reflect 

the light from the mirror across several merid- 
ians of the patient's eye, at the same time watch- 
ing the reddish fundus reflex in the pupil. If 
the movement of the fundus reflex is against that 
of the mirror in any one meridian, put a plus 
sphere before the eye, and continue to increase 
its strength until you find the weakest lens that 
will reverse the last meridian, whose movement 
was against that of the mirror. 

If there is no astigmatism the reflex will be 
equally bright in all its parts like a small full 


moon. On the other hand, if there is any astig- 
matism the shadow will have a band or ribbon- 
like appearance, the sphere being a finding for 
the meridian of the band. 

We next proceed to correct the meridian at 
right angles to the band, using a minus cylinder 
(on account of the movement being with that 
of the mirror) with its axis over the band, and 
continue to increase its strength until we find 
the weakest that will open up the band until the 
reflex is round in appearance. 

Prom the sphere now before the eye we 
deduct the power of a lens that will focus at 
the distance the mirror was held from the 
patient's eye. What is left of the sphere com- 
bined with the cylinder is the patient's Rx. 

Myopia: On the other hand, if the shadow 
moves with in all meridians, put on a weak 
minus sphere and increasing its strength until 
we find the weakest that will about reverse the 
shadow in any one meridian. If there is no 
astigmatism the shadow will move the same in 
all meridians and have .the appearance of a full 
moon. If there is any astigmatism the reddish 
fundus reflex will have a ribbon-like appearance 
(the narrower the band the higher the amount), 
the sphere always being the finding for the 
meridian in which the band is seen. The merid- 
ian at right angles to the band is still moving 
with the movement of the mirror and a minus 
cylinder with its axis over the band is used to 
reverse it while moving the mirror across the 

To the sphere already in the trial frame we 
add a minus sphere that will focus at the dis- 

taiice we are holding the mirror from the eye 
of a patient. 

In writing the Rx, put down what is left of 
the sphere after deducting or adding for the 
working distance, combining with it the full 
power of the cylinder, placing its axis at the 
degree the scratch on the lens points to on the 
trial frame. 

If the above directions are followed plus cyl- 
inders will never be used. 

The larger the error the slower the movement 
will be. Large errors are easier than small ones 
to detect and correct with the retinoscope. 

Prove up your retinoscopic test subjectively. 
If more plus can be added or less minus given 
without interfering with the vision, make the 

In using the plane mirror follow above direc- 
tions, but use plus when the shadow moves with 
and minus if against. 

When the light that is coming from the' pa- 
tient's eye (after reflection by the retina) focuses 
in front of the operator the shadow will move 
with the movement of the concave mirror. On 
the other hand, if these rays of light pass the 
operator without focusing, the movement will 
be against that of the mirror. 

The shadow moves against in Hypermetropia, 
Emmetropia and small amounts of Myopia. If 
the operator is working at 41" the eye must 
have one dioptre or more of Myopia for the 
shadow to move with the movement of the 

On page 223 are two cuts showing the fundus 
reflex in the pupil. The reflex shows white 


instead of red as it really is but they will answer 
the purpose; the first is round on the edge like 

""^Efe. ¥S?p-'5'5Jaj9UA 

a full moon, indicating no sign of astigmatism, 
while the second is ribbon or band like, showing 
there must be astigmatism between the 90th 
and 180th meridians in this case. 

Retractor (re-trac'-tor). An instrument used for 
drawing and holding the parts away while 
undergoing an operation, or for any otlier 

Retrobulbar (re-tro-bul'-bar). (L. retro = behind 
+ bulbus = bulb.) That which is situated or 
occurring behind the eyeball. 

Retrobulbar-Neuritis. Inflammation of the optic 
nerve behind the globe of the eye. 

Reversal Point. This term is used Iri retinoscopy 
to describe the change of movement of the 
shadow. For instance if the rays of light 
which are coming from the patient's eye focus 
behind the operator the shadow will always 
move against the movement of the concave 
mirror, if they are made to converge by the 
aid of a plus lens so as to focus just in front 
of the operator, the movement will be with 
that of the mirror, making it the point of 

Rheum (rume). (Gr. rheuma = a flux.) A watery 
discharge from the eyes. 

Rheumatic Iritis. Iritis caused by rheumatism. 

Rhodopsin (rho-dop'-sin). (Gr. rhodon = rose + 
ops = eye.) Visual purple; pigment of outer 
segment of retinal rods. 

Rhytidosis (rit-id-o'-sis.) (Gr. rhytidosis = a wrin- 
kling.) A wrinkling, as of the cornea. 

Riolanis Muscle. An involuntary muscle used in 
closing the eye. It reinforces the orbiculars 
and brings the margin of the lids closer to- 

Rod. Relates to tlie retina. It is one of the cell 
elements of which Jacob's Membrane is com- 
posed. These minute bodies are cylindrical in 
form, hence the term, rod (rods and cones). 

Rodent Ulcer. A -destructive ulcer beginning at 
the margin of the cornea. It is confined to the 
surface, not ^omg deeper than Bowman's 
Membrane. First (described by Dr. Mooren. 

Roentgen Rays. A forna of X rays used in deter- 
mining the presence and also the exact position 
of foreign bodies ?in ithe eyeball or orbit. 


Romberg's Symptoms (Moritz Heinrich Romberg, 
Berlin physician, 1795, 1873). Difficulty in stand- 
ing when the eyes are shut: a sign of loco- 
motor ataxia. 

Rota'tion (L. rota = a wheel.) Process of turning 
around an axis. R. of the Mirror. A term used 
in retinoscopy to indicate the movement of the 
mirror to create a movement of the light area. 

Ru-biform. Having the form or nature of red. 

Rubify. To redden. 

Ruischiana Membrane. The third or chrio- 
capillaris membrane of the choroid. 

Rutilant. Glittering, shining. 


To find the deviating power of a prism, multiply 
the difference of index by the number of de- 
grees of prism. 

To find meter curve of a lens divide dioptric 
power by difference of index. 

To find meter curve of a lens divide one meter 
by the radius of curvature on lens. 

To find difference of in^dex divide power of the 
lens by the meter curves of its radius. 

Refractive power of a lens depends upon its curva 
ture and the index of refraction of the glass 
combined. An increase of either one will pro- 
duce greater refracting power. The shorter the 
focal length the greater the refractive power. 

To find focal length of a lens surface divide the 
radius of curvature by difference of index. 

To Convert — 

Dioptries to meters of focal length, divide 
1 by the number of dioptries. 
Meters of focal length to dioptries, divide 
1 by the number of meters. 

- Dioptries to centimeters of focal length, divide 
100 by the number of dioptries. 

Centimeters of focal length to dioptries, divide 
100 by the number of centimeters. 

Dioptries to inches of focal length, divide 40 
by the number of dioptries. 

Inches of focal length to dioptries, divide 40 
by the number of inches. 

To find dioptric value of any surface, multiply the 
difference of the index of refraction by the 
number of meter curves in the radius of curva- 
ture and give it the sign of the curve of the 
denser media. Remember two meter curves in 
optics mean one-half and three meter curves, 
one-third of a meter, and so on. 
To find the angle of refraction, divide the angle 
of incidence by the index of refraction of the 
second media. 
To find the radius of curvature of any media, 
multiply the focal length desired by the differ- 
ence of the index in the two media. 

Index of Refraction = Angle of Incidence di- 
vided by Angle of Refraction. 

Angle of Incidence = Angle of Refraction 
multiplied by Index of Refraction. 

Focal Length of Curved mirrors = one-Jialf of 
the radius. 

Power of a Mirror = one meter divided by its 
focal length (catoptries). 

Metric Curve of a Mirror = one meter divided 
by the radius of the mirror. 

Radius of Mirror = one meter divided by the 
metric curve of the mirror. 
To find the dioptry power in any meridian of a 
cylinder, take the distance between the merid- 


lan of which you wish to know the power and 
the axis of the cylinder, multiply it by the 
power of the cylinder, and divide by 90. 

To find the number of millimeters to decenter a 
lens for prismatic effect, multiply the prism 
wanted by 10 and divide by the power of the 

When prismatic effect is wanted in both the 
horizontal and vertical meridians, one prism can 
be used by placing a prism obliquely. 

To find the prism to prescribe, square the power 
of the original prisms and add. Extract the 
square root of the sum, which will give you the 
power of the new prism. 

To find the meridian to place the base of the new 
prism, divide 90 by the combined power of the 
original prisms and multiply by the vertical 
prism; this gives the distance from horizontal 
to place the base of the new prism. 

To find the size of the image, focal length of 
emergent wave multiplied by size of object 
divided by focal length of incident wave; or. 
dioptric value of incident wave multiplied by 
size of object divided by dioptric value of the 
emergent wave. 

To find the size of the object, reverse the formula 

To find the size of the image on the retina, multi- 
ply the size of the object by the distance be- 
tween the nodal points and the retina, then 
divide by the distance between the nodal points 
and the object. 

To find circumference of a circle, multiply diam- 
eter by 3.1416. 

To find diameter of a circle, multiply circumfer- 
ence by .31831. 

To find area of a circle, multiply square of diam- 
eter by .7854. 

To find area of a triangle, multiply base by one- 
half perpendicular height. 

To find surface of a ball, multiply square of 
diameter by 3.141 1;. 


No. 1. No eye should be allowed to use 
accommodation at 20 feet or more. 

No. 2. Always give a hyperope the strongest 
plus that will not blur his best distant vision. 

No. 3. Give a myope the weakest minus that 
will give him best vision. Never put minus 
where it does not show returns. 

No. 4. After putting the patient in the fog. 
place the axis of your minus cylinder at right 
angles to the plainest line seen. 

No. 5. Correct presbyopia after correcting 
distant vision. 

No. 6. Before testing for muscle trouble cor- 
rect the ametropia. 


i^AC (L. saccus = a bag). A bag-like organ. 

Saemisch's Ulcer ( sa'-misb-ez). (Edwin Theodor 
Saemisch. Australian ophthalmologist. 1833.) 
Infectious corneal ulcer. 

Sarcoma (sar-ko'-mah ). (Gr. sarx ^ flesh + oma 
= tumor.) A tumor made up of a substance 
like the embryonic connective tissue. It is 
often hijrhly malignant. Sarcoma of the ciliary 



body is generally pigmented, and often passes 
unobserved until it attains considerable size as 
a brown mass, which was at first concealed 
from view by the iris. Occasionally it makes 
its first appearance at the angle of the anterior 

Schematic Eye (ske-mat'-ik). (Gr. schema = 
shape, outline, plan.) A model or drawing that 

represents a normal or emmetropic eye. Used 
in demonstrating optical laws. 

Schlemm's Canal for circular venous sinus). 
(Friedrich Schlemm, German anatomist, ]795- 
1858.) A ring-like canal, of 0.3 by 0.-5 mm. 
diameter, in the first tunic of the eye, between 
the cornea and the sclerotic. By means of the 
Spaces of Fontana it connects with the anterior 
chamber on one side, and directly communi- 
cates with the anterior ciliary veins on the 

The Spaces of Fontana are formed by the 
dividing of the tissue from Descemet's Mem- 
brane in crossing from the corneal margin to 
pass into the base of the iris, and constitute 
the ligament pectinatum iridis. 

i^LU »* io I v^v^ r\ 1 . 

Scintillation rsoin-til-la'-shun ). (L. scintilla ^^ a 
spark J A sensation of sparks before the eye. 

Scissors Movement. A peculiar movement of the 
retinal reflex, resembling the opening and shut- 
ting of a pair of scissors. It indicates a condi- 
tion of irregular astigmatism. 

Sclera Cskle'-ra). (Gr. skleros ^ hard.; The ex- 
ternal and white coat of the eyeball, The scle- 

Scleral. Pertaining to the sclera. 

Sclerectasia Tskle-rec-ta'-si-ahj. CGr. sclera -r ek- 
tasia ^- an extension.) A bulging state of the 

Sclerectomy (skle-rek'-to-myj. fOr. skleros = 
hard - ektome = excision. j Excision of a por- 
tion of the sclera. 

Sclerectasis Cskle-rek'-ta-sis). A protrusion of the 
.sclerotic coat. See Staphyloma. 

Scleriritomy Cskle-rir-it'-o-myj. (Gr. skleros = 
hard -f- iris + tome == excision.) Incision of the 
sclera and iris in anterior staphyloma. 

Scleritis Cskle-ri'-tis). CGr. skleros ^ hard — ilis 
- inflammation.) Inflammation of the sclerotic 

Sclerochoroiditis Tskle-ro-cho-roid-i'-tis). Inflam- 
mation of both the choroid and the sclerotic 
coats of the eye. 

Scleroconjunctival rskle-ro-con-junc-ti'-valj. That 
condition in which the sclera and the conjunc- 
tiva are concerned. 

Sclerocorneal Sulsus ffurrow). The angle or de- 
pression formed by the difference in the radius 
of curvature of the sclerotic and cornea. This 


angle makes the eyeball stronger and more firm 
at this point, and it is just inside this angle that 
the ciliary muscles are attached. 

Sclerocorneal (skle-ro-cor'-ne-al). Relating to the 
sclerotic coat and cornea. 

Sclerolritis (skle-ro-i-ri'-tis). An inflammation 
which involves both the iris and the sclera. 

Sclerokeratolri'tis. Inflammation of the sclera, 
cornea, and iris. 

Scleronyxis (skl'e-ro-nyx'-is). (Gr. skleros hard 
4- nyxis a pricking.) A perforation of the 
sclerotic coat. 

Sclerophthalmia (skle-rof-thar-mi-ah). (Gr. skle- 
ros = hard 4 ophthalmos = eye.) That condi- 
tion in which the sclera overlaps the cornea, so 
that only a portion of the latter remains clear. 

Scle'rosed (Gr. skleros = hard). That condition in 
which a part is affected with sclerosis; a 

Sclerosis (sclero'-sis). (Gr. sklerosis = hardness.) 
The process of becoming hard, tough, or in- 

Sclerotic (skle-rot'-ic). (Gr. skleros = hard.) The 
posterior five-sixths of the first tunic. It is 
firm, hard, and opaque; known as the white of 
the eye. It serves to give shape to the globe, 
protects its more delicate interior, and at the 
same time acts as a dark-box or camera. It is 
to this coat that the muscles are attached. Th(^ 
sclerotic is thickest in the posterior part, where 
it has a thickness of about 1 mm. It gradually 
diminishes in thickness toward the anterior 
part, becoming somewhat thicker near the cor- 

nea, because here the tendons of the recti 
muscles are attached and fused with it. The 
sclerotic consists of fine cotton-like fibers or 
connective tissues, which are united into bun- 
dles which seem 'to be woven in all directions. 
Between the bundles are found lymph-spaces, 
which are in part lined with fat cells. The 
sclera has very few blood-vessels and nerves. 
The blood-vessels are derived from the anterior 
ciliary and posterior ciliary arteries. The venous 
blood is removed by the venae vorticosae and 
the anterior ciliary veins. Its nerves are de- 
rived from the ciliary nerves. 

Scleroticectomy (skler-ot-i-kek'-to-my). (Gr. skle- 
ros = hard + ektome = excision.) An operation 
for artificial pupil by removal of a portion of 
the sclerotic. 

Sclerotomy (skle-rot'-o-me). (Gr. skleros = hard 
+ tome = incision.) Surgical incision of the 

Scotodinia (sko-to-din'-iah). (Gr. skotos = dark- 
ness -|- dine = a whirling.) Dizziness, with head- 
ache and dimness of vision. 

Scotoma (sko-to'-mah). (Gr. skotoma = darkness.) 
That condition in which there is a blind or par- 
tially blind area in the visual field. Sometimes 
the patient will complain of seeing dark, vanish- 
ing, cloudy spots before the eyes. Absolute S., a 
part of the visual field in which there is absolute 

Scotometer (sko-tom'-e-ter). An instrument for 
measuring scotoma. 

Sebaceous Cysts (L. sebum = suet -f Gr. kystis = 
bladder.) A small rounded body, the size of a 


pea, which appears in the thicker portions of 
the skin of the eyelids. 

Seborrhea (seb-or-e'-ah). (L. sebum = suet -f Gr. 
rhoia = a flow.) An abnormal secretion of the 
sebaceous glands. 

Se'cant (L. secare = to cut). (Geometry.) A 
line that cuts another, or divides it into parts. 
The secant of a circle is a line drawn from the 
circumference on one side to a point on the out- 
side of the circumference on the other. 

Secondary Axis. See Axis. 

Secondary Foci. See Focus. 

Seg'ment (L, segmentum; secare ^^ to cut). A 
section of a circle. A cylindrical lens is a seg- 
ment of a cylinder which refracts rays of light 
in all meridians but one. This meridian is known 
as the axis. A spherical lens is a segment of a 
sphere. A segment of anything is one of the 
parts into which it is divided. 

Serpiginous (ser-pij'-in-us). (L. serpere = to 
creep.) Resembling a ringworm. 

Shadow Test. See Retinoscopy. 

Sheath. A tubular case or envelope. Optic S., 
the covering of the optic nerve formed by the 
dura mater on the outside, and the pia mater 
on the inside, of the subarachnoid space. 

Shortsightedness. See Myopia. 

Sight. The sense by which external objects are 
located and seen, their color, size, and form 
described, as compared with other objects, 
through the medium of the visual organ. 

Sign. That by which anything is represented. 
The sign of addition ( + ) represents convex 

sperical and convex cylindrical lenses. The 
sign of subtraction ( — ) is used to represent 
concave spherical and concave cylindrical 

Sine. (L. sinus = sine.) The length of a per- 
pendicular drawn from one extremity of an arc 
of a circle to the diameter drawn through the 
other extremity. Sine of an angle is a circle 
whose radius is unity, the sine of the arc that 
measures the angle; in a right-angled triangle, 
the side opposite the given angle divided by the 
hypotenuse. Versed sine, that part of the diam- 
eter between the sine and the arc. 

Sinis'trad. fGr. sinister = left + ad = to.) To or 
toward the left. 

Sinus (si'-nus). (L. "gulf.") A hollow cavity. 
Frontal Sinus, one of the two irregular cavities 
in the frontal bone containing air and commu- 
nicating with the nose through a funnel-shaped 
passage. Occipital Sinus is the smallest of the 
cranial sinuses, occasionally there are two. It 
is situated in the attached margin of the falx 
cerebelli, opening into the torcular Herophili. 
Lateral Sinus, two veins of the dura running 
along the crucial ridge of the occipital bone. 
Cavernous Sinus, venous cavities, starting be- 
hind the sphenoidal fissure, running back on the 
side of the pituitary fossa, and joining the su- 
perior and inferior petrosal sinuses. Each cav- 
ernous sinus receives anteriorly the superior 
ophthalmic vein through the sphenoidal fissure. 
on the inner wall of each sinus is the internal 
corotid artery, filaments of the corotid plexus, 
abducent nerve; and on the outer wall, the 


trochlear, ophthalmic, oculo motor and the 
maxillary division of the trigeminal nerves. 

Skiascope (ski'-as-kope). (Gr. skia = shadow + 
skopeo ^= I examine.) Better known as the 

Skiascopy. (Gr. skia =^ shadow -f- skopeo = I ex- 
amine.) See Retinoscopy. 

Snellen, M. D., Prof. H. Born in Holland. A pro- 
fessor of ophthalmology occupying the chair at 
the University at Utrecht, Holland. A pupil of 
Dr. F. C. Bonders, whom he succeeded in prac- 
tice and his professorship. He devised a chart 
consisting of letters and symbols by which the 
subjective means of measuring the range of 
vision could be uniformly and scientifically de- 
termined. It is held by Snellen that in order to 
distinguish one letter from another the eye must 
be able to distinguish the spaces between the 
lines which correspond to a visual angle of 1'. 
This is true for certain letters, as, for instance, 
to differentiate between O and C, where the eye 

Snellen Chart. 

must distinguish the white space which inter- 
rupts the circle in C. The same is true for 
E and F, but the principle is not applicable to 
the other letters of his series. In a lecture on 

refraction by Landolt, we learn of what great 
advantage it is to determine the visual aciite- 
ness and the refraction at the same time. We 
must determine the refraction at such a dis- 
tance as shall exclude the accommodation as 
much as possible. For this a distance of twenty 
feet, or six metres, is necessary. We therefore 
place our test type at 20 F, and see what are the 
smallest characters which each eye, separately, 
can distinguish. These types are so designed 
that at the distance at which they should be 
seen they each subtend an angle of 5' at the eye. 
And when the letters marked 20, or 6 M, are 
read from 20 F, vision is said to be normal, and 
an eye with normal vision can read any of the 
letters on the chart at the distance at which 
they are marked. 

Snow-bllndness. Long exposure of the eyes to the 
glare from snow gives rise to an acute conjunc- 
tivitis, attended with intense pain, photophobia, 
and occasionally conjunctival hemorrhages. 

Socket (sok'-ket). (L, soccus = a show, a sock.) 
A hollow part into which a corresponding part 

Spasm. (L. spasmus = I draw.) An involuntary 
contraction of a muscle. Spasm of accommoda- 
tion is a spasmodic contraction of the ciliary 
muscles, thus increasing the convexity of the 
crystalline lens and making the eye appear to 
have a higher refractive power. There are two 
kinds — tonic and clonic. Tonic s. is where the 
spasm persists for a considerable time, and 
Clonic s. is where the muscles contract and re- 
lax intermittently. 


Spectacles. (L. spectare ^ to regard.) A pair of 
lenses mounted in frames with temples attached. 

Spectrum (spec'-tnim). White light is composed 
of all the colored lights known, and when it is 
separated by a prism or other means and 
thrown on a white screen, in an otherwise dark 
room, a band of colors resembling a rainbow 
is seen. This is called a prismatic or solar 

Of the seven primary colors which form the 
spectrum, Violet is refracted the most, then 
Indigo, Blue, Green, Yellow, Orange i',nd Red 
the least. There are also invisible rays called 
"ultra'-red, and ''ultra"-violet beyond its ap- 
parent boundaries. 

Ocular Spectrum color seen by an eye where 
none exists. 

Diffraction Spectrum is a spectrum produced 
by diffraction. 

Chromatic Spectrum is the visible colored 
rays of the solar spectrum, showing the seven 
principal colors in their order and covering the 
larger portion of the space of the w^ole spec- 

Sphenoid (sphe'-noid). (Gr. sphen = wedge -f 
eidos = resemblance.) Sphenoid Bone. A bone 
situated at the upper and back part of the 
orbits on the median line, at the base of the 
cranium. It articulates with all the other bones 
of that cavity, and strengthens their union. 
When seen from above it resembles a bat with 
its wings extended. 

Sphere (sfer). (3r. sphaira = a ball.) A ball- 
like body. 

Spherical. Having the form of a sphere. Spherical 
Lens is one the curved surface of which is a 
segment of a sphere and is known as a lens 
with the same refracting power in all its 
meridians. There are three ways to grind a 
plus or minus sphere of the same value; 
namely, bi-concave, plano-concave, periscopic- 
concave, bi-convex, plano-convex, periscopic- 
convex. See Lenses. 

Spheroid (sphe'-roid). (Gr. sphaira = sphere -h 
eidos = resemblance.) That which resembles a 
sphere in shape. 

Spherometer. (Gr. sphaira = sphere + metron ^ 
measure.) An apparatus for measuring the 
curvature of a surface. 

Sphincter (sphinc'-ter). (Gr. sphinkter = a band.) 
A ring-like muscle. The sphincter muscle of 
the iris when contracted closes down the pupil. 
"When relaxed allows the pupil to become 

Spintherism (spin'-ther-ism). (Gr. spinther = 
spark.) That condition in which the patient 
complains of seeing star-like flashes of light. 

Squamous (skwa'-mus). Scaly. 

Square (skwar). (L. quatuor = four.) (a) An 
equilateral rectangle, (b) The second power of 
a number, (c) To raise a number to the second 

Squint. (Fr. guigner to wink or direct with one 
eye.) The act of half closing the eyelids while 
viewing an object. The word squint is some- 
times used to denote strabismus. 

Staphyloma (sta-fy-lo'-mah). (Gr, staphyle =^ 
grape + oma = tumor.) A bulging of the cor- 

on I'ln A LM 1( " I >ICTIONAIiY 


nea or sclera. Anterior s., a bul^inK forward of 
the anterior portion of the eye. Posterior s., 
backward bulging of the posterior pole of the 
o> e. 

Stat'ic. . (Or. statikos causing to stand.) Not 
in motion: in a state of rest. The static refrac- 
tion is the refraction of the eye with the mus- 
cles of accommodation at rest; just the reverse 
to dynamic refraction. 

Steato'sis. (dr. stear (steat) == tallow -f- sufTix 
osis condition.) That condition in which we 
have fatty degeneration; disease of the sebace- 
ous glands. 

Stenopaic Slit (sten-o-pa'-ic). (Gr. stenos = 
narrow -f ope = opening.) An accessory to be 
found in any complete trial case, and consists 
of an opaque disc with a slit about an inch long 

and one millimetre wide. It is used for the pur- 
p().s«' of linding the principal meridians in cases 
of regular astigmatism. If vision is near nor- 
mal it is best to fog or blur it a line or two with 
a plus sphere, then place the disc in the trial 

frame in front of the eye we are about to ex- 
amine, while the other is covered by the opaque 
disc. Instruct the patient to revolve the disc in 
the trial frame while trying to see the letters 
on Snellen's test type at a distance of twenty 
feet (never tlie astigmatic wheel) and stop when 
the best vision is obtained, thus locating the 
principal meridian with least error. We then 
DOte the degree mark on the trial frame to 
which the slit is pointing and make a right angle 
cross on a piece of paper showing this meridian 
and the one at right angles. We now proceed 
to correct the error by placing spheres over the 
slit until we find the strongest plus or weakest 
minus that allows the best vision, writing the 
amount on the arm of the cross corresponding to 
the slit. Then revolve the slit 90° and fit this 
meridian as above, writing the amount on the 
other arm of the cross. From this cross we 
write the Rx without any change. This will 
represent the Ametropia. 

Stereoscope (ster'-e-o-scope) . (Gv. stereos = solid 
-5- skopeo = I view.) An instrument composed 
of two prisms arranged in such a way that two 
separate pictures of the same kind may be seen 
as one. This instrument makes the picture 
more natural, as the objects appear to stand 

Stereoscopic Vision (ster-e-o-scop'-ic). Where we 
have equal vision with the two eyes and the 
objects appear to stand out in solid form, and 
are not seen as flat pictures. 

Stilling's Canal. (Benedict Stilling, German anato- 
mist, 1810-1879.) A small canal leading from 



the optic disc through the vitreous humor to the 
lens of the eye. See Anatomy. 

Stiilicidium (stil-li-sid'-i-um). (L. stilla = drop -f- 
cadere = to fall.) An overflowing of the tears 
upon the check due to a stricture of or a nar- 
rowing of the nasal duct. Same as epiphora. 

Stilus fsti'-lus). (L. stilus = a stake.) A small 
instrument made of gold or silver used for 
dilating the lacrimal duct. 

Stoke's Lenses. (William Stokes. Dublin physi- 
cian. 1804-1878.) An instrument that was used 
in the diagnosis of astigmatism. 

Stop-needle. A needle with a disc attached to 
regulate the depth of penetration. 

Strablsmometer (strab-is-mom'-e-ter). (Gr. stra- 
bismos + metron = measure.) An instrument 
for measuring the degrees of strabismus. 

Strabismus (stra-bis'-mus). (Gr. strabismos = 
distorted.) (Cross-eyed.) That condition in 
which the eyes are not parallel for distant 
vision. The visual axis of one eye only is di- 
rected towards the object looked at; this is 
known as the fixing eye, while the other is 
known as the deviating eye. It is caused by 
anything which develops preponderance of 
power in a muscle, either directly or indirectly. 
It may be due to an uncorrected error of re- 
fraction; or from anything which prevents 
binocular vision, such as cataract, corneal opaci- 
ties, displaced macula lutea, a short, long, or 
paralyzed muscle. However, it is well to cor- 
rect any ametropia, for when a person has an 
error of refraction in one eye that interferes 
with the vision of its fellow, he will learn to 

turn the eye with the error to one side. Alter- 
nating s., affecting both eyes equally, but not at 
the same time. Concomitant s. is that form of 
strabismus in which one eye, although deviated, 
always moves with the other, so that the 

One Eye turning in. 

Both Eyes turning in. 

Both Eyes turning out. 

amount of deflection remains the same. Para- 
lytic s. is due to paralysis of one or more of the 
extrinsic muscles, and the eye remains station- 
ary. Hypermetropia is responsible for 80 per 
cent of converging strabismus on account of 
the ciliary muscles and the internal rectus 


muscles being supplied by one and the same 

When the eye attempts to accommodate in 
order to overcome the hypermetropia, the in- 
ternal rectus will contract, and if the patient 
has not the nerve energy to control the external 
rectus, the eye will turn in. See Heterotropia. 

Strabotomy (stra-bot'-o-my). (Gr. "oblique" + 
tome= a cutting.) An operation calling for the 
outting of an ocular tendon for relief in cases of 

'otrain. (L. stringere = to bind.) Injury from 
over-use. Ciliary s., the result of overwork of 
the ciliary muscles in hypermetropia and some- 
times in emmetropia. Muscular s., overwork of 
the extrinsic muscles as in heterophoria. 
Retinal s., fatigue of the retina caused by too 
strong light or from over-use in a normal light. 
The eye should be protected from all direct 
rays of light, as only reflected light is neces- 
sary for vision. 

Stroma (stro'-ma). (Gr. "I spread out.") The 
foundation tissue or support of a formation. 

Stye ("to rise") or Hordiolum. A small boil af- 
fecting the connective tissue near the edge of 
the eyelid, sometimes several appear at once, 
or there may be a succession of them. They 
cause swelling of the lid. In a day or two the 
swelling increases, with considerable pain, and 
the skin over it becomes red, afterwards show- 
ing a yellowish discoloration at the center that 
finally opens near the border of the lid, with a 
discharge of pus. After which the inflammatory 
symptoms abate and the cavity soon closes. 

Treatment: Small poultices or hot fomenta- 
tions until pus forms, then open by incision 
parallel to the edge of the lid. General health 
requires attention if eye strain is not the cause. 

Subarach'noid Space. (L. sub = under + Gr. 
arachne ^^ cobweb + eidos = resemblance.) 
That space between the dura mater and the pia . 
mater which forms the optic sheath and the 
Capsule of Tenon. 

Subconjunctival (sub-con-junc-ti'-val). That which 
is situated just beneath the conjunctiva. 

Subjective (sub-jec'-tive). That which pertains 
to, or is perceived by, an individual. Not per- 
ceptible to any other person. It refers to the 
patient as he sees objects or feels concerning 
his own impressions. 

Subla'tio Ret'inae. (L. sublatus = taken away -f 
rete = net.) Detachment of the retina. 

Subluxa'tion. (L. sub = under -f luxare = to dis- 
locate.) Where the lens of the eye is a little 
displaced, subluxation may consist in the lens 
being turned a little obliquely, so that one end 
of it looks somewhat forward. This condition 
may be recognized from the unequal depth of 
the anterior chamber. In cases of luxation, 
that is, where the lens has left its place fn its 
capsule, so that it partly covers the pupil, that 
part of the pupil which is a deep black has no 
lens, while the part which contains the lens 
would be of a delicate gray. Any dislocation 
of the lens entails a considerable disturbance of 
vision. If the lens still lies behind the pupil the 
eye becomes very myopic, because the lens is | 
allowed to assume its maximum convexity on ' 



account of separating from the suspensory liga- 
ments which keep it elongated when the eye is 
at rest. Invariably any tear in the suspen- 
sory ligament results in soft cataract. Added 
to this is a considerable degree of astigmatism. 
Dislocations of the lens usually entail second- 
ary consequences which may be extremely dis- 
astrous to the eye, but in those cases in which 
the dislocation entails no further injurious con- 
sequences than the disturbance of vision, the 
treatment consists in prescribing suitable 

Suborbital (sub-or'-bit-al). Beneath the orbit. 

Subretinal (sub-ret'-in-al). Situated beneath the 

Subtraction (sub-trak'-shun). (L. sub = under -f- 
trahere =^ draw.) The operation of finding the 
difference between two numbers. 

Subvolution (sub-vo-lu'-shun). (L. sub = under + 
volvere =^ to turn.) An operation for the re- 
moval of a pterygium. 

Suction (suc'-shun). (L. sugere = to suck.) A 
method by which fluid is withdrawn. 

Suffusion (suf-fu'-zhun). L, suffundere = to pour 
down.) State of being blood-shot, or of being- 
moistened. A suffusion of tears is an excess of 
the flow of tears. 

Super Cilia. fUpper hairs.) (L. super = above -f- 
cilium eyelash.) The eyebrows. 

Superciliary (su-per-cil'-i-a-ry). That which per- 
tains to the eyebrow. 

Supra Choroidal Space. The space between the 
sclerotic and choroid. 

Supraduction, Sursumvergence. (L. sursum = up- 
ward + vergere = to bend. The act or power of 
turning one eye above its fellow. 

Supraorbital (su-pra-or'-bi-tal). (L. supra = above 
+ orbita = orbit.) Located over the orbits. 

Supra-orbital Foramen. A small passage in the 
Supra-orbital Ridge through which passes the 
supra-orbital nerve (a branch of the fifth) 
artery and vein. 

Surface (ser'-fas). (L. superficies = the upper 
face.) The bounding or limiting parts of a solid. 

Sursumduction (sur-sum-duk'-shun), (L. sursum 
= upward + ducere = to draw.) The act of 
turning one eye upward independent of its fel- 
low. The test is made by placing the base of 
the prism down until we find the strongest 
which the eyes can see an object singly. It is 
seldom more than 3°. 

Sursumvergence (sur-sum-vur'-jenz). 
= upward + vergere = to turn.) 
turning of the eye. 

Sursumversion (sur-sum-vur'-shun). 
= upward + vertere = to turn.) 
turning the eyes upward. 

Suspensory (sus-pen'-so-ry). (L. suspendere 
suspend.) Serving to hold up a part. 

Suspensory Ligaments. The hyaloid membrane 
forms the hyaloid sac in which the vitreous 
humor is contained. It runs forward up over 
the ciliary body, divides and forms the suspen- 
sory ligaments, which are attached to the lens 
capsule. C. B. Lockwood. in a journal of Anat- 
omy and Physiology, vol. XX., part I. — Ed. of 








act of 



15th English edition, has also described a thick- 
ening of the lower part of the Capsule of Tenon, 
which he has named the suspensory ligament of 
the eye. It is slung like a hammock below the 
eyeball, being expanded in the center and nar- 
row at its extremities, which are attached to 
the malar and lachrymal bones respectively. 

Suture fsu'-ture). (L. sutura = a seam.) The 
serrated junction of the intracranial bones. 
Dovetail joint. 

Sylvius, Aqueduct of. A passage from the third 
to the fourth ventricle of the brain. 

Symblepharon (sym-blef'-ar-on). (Gr. syn = to- 
gether + blephron = eyelid.) Adhesion of the 
lids to the eyeball. This develops whenever 
two opposed spots of the conjunctiva of the lid 
and of the eyeball have raw surfaces which 
come into contact with each other, and in con- 
sequence become adherent. Causes which can 
give rise to the formation of raw surfaces upon 
the conjunctiva are burns by the action of heat, 
burns from caustic substances, diphtheria, oper- 
ations, ulcers of all kinds, etc. 

Sympathetic Ophthalmitis (sym-pa-thet'-ik of-thal- 
mi'-tis). (Gr. syn = with + pathos = suffering 
+ ophthalmos = eye -f itis.) An inflammatory 
condition of the iris and ciliary body, which is 
developed through an injury or disease of the 
opposite eye. 

Symptoms. (Gr. syn = with + ptoma = I fall.) A 
perceptible change which indicates disease, or 
that which indicates the existence of something 
else. See Objective and Subjective Symptoms. 

Synchysis (syn'-chy-sis). (Gr. confusion.) Lique- 

faction of the vitreous. When observing opaci- 
ties of the vitreous with the ophthalmoscope, 
we see that most of them float about freely in 
the vitreous. From this we would assume that 
the framework of the vitreous must have been 
destroyed, so that this body Itself is converted 
into a perfectly liquid mass. 

Syndesmi'tis. (Gr. syndesmos = ligament + itis 
= inflammation.) That condition in which 
there is inflammation of a ligament or of the 

Synechia (syn-e'-chi-ah). (Gr. synecheia = con- 
tinuous.) Adhesion, as of the iris to the lens 
or cornea. Posterior s., adhesions of the iris to 
the lens capsule. Anterior s., adhesions of the 
iris to the cornea. 

Synizesis (sin-iz-e'-sis). (Gr. "a falling in.") Con- 
traction of the pupil of the eye. 

Synophthalmus (syn-of-thal'-mus). (Gr. syn = to- 
gether + ophthalmos = eye.) A one-eyed mon- 

Syntropic (sin-trop'-ik). (Gr. syn = together + 
tropikos = turning.) Turned in the same direc- 

System. (Gr. systema = to place together.) A 
bodily organism. An assemblage of parts or 
organs which unite in a common function. 

JL • An abbreviation for tension or temperature. 

Tangent (tan'-gent). (L. tangere = to touch.) 
Touching at a single point; specifically meeting 
a curve or surface at a point and having at that 


-point the same direction as the curve or sur- 
face — said of a straight line, curve or surface; 
as. a line tangent to a curve; a curve tangent to 
a surface; tangent surfaces. Tangent plane is 
a plane which touches a surface in a point or 

Tapetum (ta-pe'-tum). (L. "a carpet.") The 
luminosity seen in the eyes of many beasts. A 
lustrous, greenish membrane seen in the eyes 
of cats and many animals that require night 

Tarsal Cartilages ftar'-sal kar'-til-aj-es). (Gr. 
tarsos = a wicker work frame + cartilago == 
gristle.) That which forms the tough skeleton 
layer of the eyelids, giving them rigidity of 
form and affording them firm support. The 
shape is like that of the lids being fastened 
around the edge of the orbit. The tarsus of the 
upper lid is broader than that of the lower. 

Tarsitis (tars-i'-tis). (Gr. tarsos = a wicker work 
frame -f- itis = inflammation.) An inflammation 
involving the tarsal cartilages. 

Tarsoplasty (tar'-so-plas-ty). (Gr. tarsos + plasso 
= I form.) Plastic surgery of the tarsus. 

Tarsorrhaphy (tar-sor'-a-fe). (Gr. tarsos + rhaphe 
= a stitching.) An operation upon the eyelids. 

Tarsotomy (tar-sot'-o-my). (Gr. tarsos -j- tome = 
incision.) A surgical operation which involves 
the cutting of the tarsal cartilages. 

Tarsus (tar'-sus). (Gr. tarsos = a wicker work 
frame.) That which forms the skeleton of the 
eyelid, giving it rigidity of form and affording it 
firm support. The tarsus of the upper lid is 
broader than that of the lower 

Tears. The watery secretion of the lacrimal 

Teichopsia (tei-kop'-si-ah). (Gr. teichos = wall + 
opsis = vision). A luminous appearance before 
the eyes, with a zigzag, wall-like outline. 

Telangiectasis (tel-an-je-ek'-ta-sis). (Gr. telos = 
end == angeion = vessel + ektasis = a stretch- 
ing out.) Dilatation of capillaries. 

Tendency (tend'-en-cy). A disposition on the part 
of a muscle to incline toward certain directions. 

Tendon (ten'-don). (L. tendo = I stretch.) The 
fibrous cords by which the muscles are 

Tendons. (Sinew.) White, glistening, fibrous 
cords, varying in length and thickness, some- 
times round, sometimes flattened, of consider- 
able strength and devoid of elasticity. Apon- 
euroses are flattened or ribbon-shaped tendons. 
They are without nerves and have very few 
blood-vessels. Tendons pass through all mus- 
cles and form their attachment at each end. 

Tendon of Lockwood gives origin to the 
Superior Internal and upper head of the Ex- 
ternal recti muscles. It is part of the ligament 
of Zinn. 

Tenonitis (ten-on-i'-tis). (Gr. tenon = tendon + 
itis.) Inflammation of the Capsule of Teno^^. 

Tenon's Capsule. (Jacques Tenon, French anat- 
omist, 1724-1816.) (Tunica vaginalis oculi.) The 
cup-like thin membranes which envelop the eye- 
ball, covering the sclera from the optic nerve to 
the ciliary region, where it joins the ocular sub- 
conjunctival tissue. The space within the orbit 


which is not occupied by the eyeball, its mus- 
cles, nerves, vessels or other parts belonging to 
it is completely filled with soft, fat and deli- 
cate, elastic connective tissue. In various places 
this tissue is condensed into two layers of con- 
siderable strength. One layer investing the 
sclera of the eyeball and the other lining the 
cushion of fat in which the eyeball rests. These 
two layers lined with flattened endothelial cells 
encloses a lymph space which communicates 
with the subdural and subarachnoid lymph 
spaces of the optic sheath. They are traversed 
by delicate bands of connective, elastic tissue, 
thus forming a flexible socket, in which the eye- 
ball rotates by means of its muscles. This cap- 
sule is perforated by the ocular muscles and is 
reflected back on each as a tubular sheath. 
These two layers are sometimes referred to as 
the dura mater and pia mater, owing to their 
connection through the optic sheath, with the 
dura and pia mater which lines the skull. 

Tenotomy (ten-ot'-om-e). (Gr. tenon = tendon + 
tome = incision.) An operation for cutting or 
dividing the tendon of a muscle. 

Tension (ten'-shun). (L. tendere = to stretch.) 
The condition of being stretched or tense. 

Tensor-tarsi Muscle (ten-sor-tar'-si). A very small 
muscle located at the inner canthus of the eye. 
It takes its origin at the crest of the lacrimal 
bone, and is inserted into the tarsal cartilage of 
the eye-lids. It is supplied by the facial nerve. 
Its use is to compress the puncta and lacrimal 

Test. (L. testis = witness.) An examination or 

trial. T. types, letters of various shapes and 
sizes used in testing visual power. 
Tetranopsia (tet-ran-op'-si-a). (Gr. tetra = four + 
an - away + opsis — vision.) Obliteration of 
one-fourth of the visual field. 

Thermometer (ther-mom'-e-ter). (Gr. therme = 
heat + metron ^^ measure.) An instrument by 
which temperature is measured. 

Thalamus (thal'-a-mus). (A room; a bed.) The 
place in which a nerve originates, Optic Thal- 
amus. A mass of nerve matter on both sides of 
the third ventricle of the brain. 

Thrombosis (throm-bo'-sis). (Gr. thrombosis = a 
curdling, a clot.) The formation of a blood-clot 
in a vessel at the point of obstruction. 

Thyroid (thi'-roid). (Gr. thyreos = an oblong 
shield + eidos = form.) Shield-shaped. T. Gland 
is a vascular body situated at the front and 
sides of the neck, and extending upwards upon 
each side of the larynx. It is a single gland, 
varying greatly in size in different individuals. 

Tinea Tarsi. Blepharitis marginalis. See Bleph- 

Tobacco Amaurosis. (Gr. amauros — obscure.) A 
dimness of vision caused by the excessive use 
of tobacco, which acts directly upon the nervous 
system. The reduction in the visual acuity is 
almost always the same in both eyes. Treat- 
ment consists, first of all, in abstinence from 
tobacco, and it is probable that in light cases 
this alone is sufficient to effect a cure. 

Tonic Spasm. (Gr. tone + "to draw.") A con- 
tinuous involuntary contraction of the ciliary 


muscles. This condition may exist in any 

Tonometer ( to-nom'-e-ter). (Gr. tones — tone 4- 
metron measure.) An instrument for meas- 
uring the tension of the eyeball. 

Tonic Lens. A lens with a sphere and a cylinder 
on the same side, usually periscopic in shape. 
See Lens. 

Torsion (tor'-shun). (L. torquere = to twist.) A 

Toxic Amblyopia. (Gr. toxikon = poison.) Am- 
blyopia caused by a poison, a common cause 
being excessive use of tobacco or liquor or both. 

Trachoma (tra-ko'-mah). (Gr. trachys ^ rough.) 
Granular conjunctivitis. Characterized by 
slowly progressive changes in the conjunctiva 
of the eyelids, in consequence of which this 
membrane becomes thickened, vascular, and 
roughened by firm, round elevations, instead of 
being pale, thin and smooth. Granular disease 
is very important, because it greatly increases 
the susceptibility of the conjunctiva to take on 
acute inflammation and to produce contagious 
discharge. It often gives rise to deformities of 
the lid and to serious damage of the cornea. 
The conditions which favor the development 
and spread of trachoma are unclean and over- 
crowded surroundings in which ventilation is 
neglected, and the locality is damp. The disease 
is common among school children who are 
poorly nourished. 

Tract. See Optic Tract. 

Transection (tran sek'-shun). (L. trans -- across 

-f sectio; secare = tc cut.) A section made 
across a long axis. 

Transillumination (trans-il-lu-min-a'-shun). (L. 
trans = through + illuminare = to light up.) 
The inspection of the interior of an organ by 
means of a strong light. 

Transit. (L. trans = through.) A passing across. 
A term used in retinoscopy to indicate move- 
ment of the light area. 

Transi'tional Zone. The posterior part of the lens 
sac during the stage of growth. 

Translu'cent. (L. trans = through + lucere = to 
shine.) The quality of transmitting rays of light 
without the object being distinctly seen. 
(Frosted glass.) 

Transparent. (L. trans = through + parere = to 
appear.) Having the property of being clearly 
seen through. 

Transposition (trans-po-si'-shun). (L. trans = 
across + ponere = to place.) Changing the 
form of an optical prescription without changing 
its optical value. To transpose a lens is to 
change its curves without changing its refrac- 
tive value. 

To transpose an optical prescription is to 
change the form or shape of the lens without 
changing its optical value, periscopic effect be- 
ing the prime and important feature in most 
instances. The term periscopic is applied to 
lenses having concavo-convex surfaces, which 
enable the eye to view with equal likeness on 
all sides. When lenses are not of this descrip- 
tion the desired result may be obtained by the 
following rules: 


When the sign of the sphere and cylinder are 
alike (i. e., both plus or both minus) add them 
together for the new sphere, prefixing the same 

When the sign of the sphere and cylinder are 
different (i. e., one plus and the other minus) 
subtract for the new sphere, prefixing the sign 
of the larger number. 

Always change the sign of the cylinder to the 
opposite, but do not change its value. 

Always change the axis to right angle (i. e., 
inove it 90°). 

For transposition of simple cylinders, use the 
lollowing rule: Use the numerical value of 
your cylinder for the new sphere, prefixing the 
same sign, and for the new cylinder use the 
same value as the original, but prefix the oppo- 
site sign and change the axis to right angle. 

To co-nvert cross cylinders into sphero-cylin- 
ders, apply the fpllowing rule: Use the smaller 
number for your sphere (if the numbers are 
alike, take either one, keeping its own sign), 
and when the signs of the cylinders are alike 
(i. e., both plus or both minus) subtract them 
for your cylinder, prefixing the same sign. 
When the signs are unlike (i. e., one plus and 
the other minus) add them for your cylinder, 
prefixing the sign of the remaining cylinder, 
and also its axis. 

If, after transposing cross cylinders, your pre- 
scription is not periscopic, make it so by trans- 
posing again by one of above rules. 

Below find a few examples in transposition, 
with their ansvvers: 

Example, + 3 sph. 3 — 2 cyl. ax. 60. 

Answer, -}- 1 sph. ^ + 2 cyl. ax. 150. 

Example, + 2 sph. 3 +2 cyl. ax. 90. . 

Answer, + 4 sph. 3 — 2 cyl. ax. 180. 

Example, + 4 cyl. ax. 45 3 -f 2 cyl. ax. 135. 

Answer, + 2 sph. 3 +2 cyl. ax. 45. 

Example, — 3 cyl. ax. 20 3 + 3 cyl. ax. 110. 

Answer, — 3 sph. 3+6 cyl. ax. 110. 

Example, + 1 cyl. ax. 60. 

Answer, -f 1 sph. 3 — 1 cyl. ax. 150. 

Writing a prescription from a cross is not 
transposing. We must first have a written pre- 
scription before it can be transposed. 

In order to give the patient glasses which 
give them the best possible results, it will be 
necessary to know how to build lenses of dif- 
ferent shapes, for instance: 

Biconvex, biconcave, piano convex, piano con- 
cave, periscopic and toric. 

Lenses have two kinds of power, minus and 
plus — the former being thinner in the center 
and the latter thinner at the edge. These lenses 
can be made up as a sphere or cylinder. 

A sphere is a lens with the same power in 
all its meridians. 


Cut sliowfng how the nieiidians of an eye are numbered 
from right to left. 



A meridian is any straight line drawn from 
edge to edge over its optical center. 

The optical center being a point in line with 
the thickest part of a plus and the thinnest 
part of a minus lens. 

A cylinder is a lens with power in all merid- 
ians but one, this one, having no power and is 
called its axis. The full power of a cylinder is 
always found at right angles to its axis. 

In the following diagram we will use a plus 
four dioptry sphere and plus four cylinder for 

Notice that the power is the same in all 
meridians of a sphere, while those of a cylinder 
vary in power. 

An optical prescription is nothing more than 
an order for a lens of a given power and shape, 
and when it is transposed, the shape is changed 
but not its optical value (or power) ; for in- 
stance, we take the following prescription: 

+ 4 sph. 3+4 cyl. ax. 180. 
which reads plus four sphere combined with a 
plus four cylinder, axis 180. The optician, on 
receiving this prescription, will grind the plus 
four sphere on one side of the lens and a plus 
four cvlinder on the other and cut it out, so 

that the axis of the cylinder will be at 180". 
This lens being plus on both sides is known as 
a biconvex lens. 

+ 3. 

In this example we have the sphere and cylin- 
der separated and together, showing their com- 
bined powers and also their appearance from 
the side. It should be noted that the sphere 
does not change its value under the axis of the 
cylinder, thus forming one of its principal 

In order to change the shape of this lens we 
must apply the following rule: 

"When the signs of the sphere and cylinder 
are alike, that is, both plus or both minus, add 
the values together for your new sphere which 
would be plus eight, then change the sign of 
your cylinder, which makes it minus, but do not 
change its value. Change its axis 90°, taking 90 



from 180 leaves 90, thus + 4 sph. 3+4 cyl. ax. 
180 transposed gives you + 8. sph. 3 — 4. cyl. 
ax. 90°. ^ 

In the latter prescription you have what is 
known as a periscopic lens, one side plus and 
the other side minus. 

■i-8 ^ 

This shape lens is much preferred by the 
Refractionist of today on account of its appear- 
ance and comfort to the patient. 

Trapezoid (tra-pe'-zoid). (Gr. trapeza = table + 
eidos = form.) A quadrilateral having two 
parallel sides. 

Traumatic (trau-mat'-ik). Of, caused by. or per- 
taining to, an injury. 

Trembling Eyes. See Nystagmus. 

Trial Case (and how to use it). The ordinary 
trial case contains about thirty pairs of convex 
and the same number of concave spherical 
lenses, ranging from 0.12-D. up to 20-Dioptries ; 

twenty pairs of convex and the same number 
of concave cylindrical lenses ranging from 
0.12-D, up to 6-Dioptry; at least ten prisms from 
1 to 10°; a plain red tinted glass; some shades 
of smoked glasses; an opaque disc; stenopaic 
slit; pinhole disc; a ground glass disc; a Mad- 
dox rod, or double prism, and a retinoscope; 
two trial frames, one having three cells to be 

Trial Case. 

used in fitting, the other two cells, so that we 
may allow a patient to wear his correction for 
a short time and still have one to use. The 
patient is seated 20 feet from the test card, 
which must be well illuminated, and shades 
arranged so that the light will throw no direct 
rays on the patient's face. Place a small table 
holding your trial case on the patient's right 
hand side; seat yourself at the table with your 
back to the reading chart. Now you will find 
yourself in a very easy position to change the 
lenses. The trial frame is placed upon the pa- 
tient's face and adjusted so that he will look 


through the center of the lenses, having the 
frame as near the face as possible. Now you 
are in a position to begin testing. First place 
the opaque disc over the left eye, always making 
it a rule to test the right eye first, as you will 
tind all prescription blanks made out in this 
way. Now instruct your patient to read the 
smallest line of letters that he can see with the 
naked eye. We will say in this case he read the 
line marked 60. As he is seated 20 feet from 
the chart, vision with the naked eye is 20/60. 
You must always remember what the vision 
with the naked eye is, so that you will be able 
to judge whether or not the vision is improved 
with the correction. Now take a plus sphere 
from the trial case, say plus .50-D., place it be- 
fore the right eye, asking the patient to again 
read the smallest type that he can see clearly. 
Should the patient not read as well, the case 
may be one of emmetropia, myopia, or astig- 
matism; but, on the other hand, if he reads 
just the same as before, or a line better, it is 
a case of hypermetropia, and we will now pro- 
ceed to work out a case of each kind. 

Hypermetropia. In this case we will say he 
read line numbered 50. Then his vision will be 
20/50. Now we place before this right eye a 
plus ..jO sphere, and if the patient reads the 
same or a line better, it is surely a case of 
hypermetropia. Now, as a plus lens will always 
relax accommodation, and we do not want any 
eye to accommodate for 20 feet, or farther, we 
will add more plus in the following manner: 
take a plus 1 sphere and place it in the second 
cell of your trial frame, then withdraw the plus 

.50. In this way the eye will not be left uncov- 
ered; again ask the patient to read, and should 
he read as well as before we will increase the 
plus sphere until the smallest line that he reads 
becomes blurred, then we will know that he has 
relaxed all the accommodation he had in use: 
that being the object of the fogging system. 
Then draw the patient's attention to astigmatic 


= USO' 

Astigmatic WheeL 

wheel, asking him, 'are all the spokes in the 
wheel equally clear and of the same density?" 
If there is no astigmatism the patient will see 
the wheel uniformly. In that case we would 
ask him to again look at the reading chart, and 
gradually reduce the strength of the plus 
sphere, until we find the strongest that will 
allow the best vision. This will be his correc- 
tion. On the other hand, had the patient told 
you that the wheel did not look uniform, but 
that one or more of the spokes were much 
darker, it would indicate astigmatism, and we 
would ask the patient which spoke appeared the 
most clearly. Now, suppose he says "it is the 
vertical," or the spoke running from 12 to 6, 
then as we wish to know if the patient sees the 


spoke quite clearly, we will ask him to count 
the lines in the spoke. Should he count the 
right number we will consider he is seeing it 
clearly, and to make sure that he is not still 
accommodating before we correct the astig- 
matism, we will increase the plus sphere (al- 
ready in the trial frame) until we just about 
blur all the spokes in the wheel; then reduce 
your sphere a quarter D. at a time, at the same 
time asking the patient to inform you when one 
of the spokes comes out clearly, and he can count 
the lines. Whatever plus sphere you have in 
the frame at this time, place in the cell nearest 
the eye; or, a better way would be to place a 
plus sphere of the same strength as the one 
already in the frame in the cell nearest the eye 
before removing the one in front. In this way 
you will move the lens in the frame without 
exposing the naked eye. It will then be out of 
the way while using the cylinder. Now take 
from your trial case the weakest minus cylinder 
and place it in the trial frame with the axis at 
right angles to the plainest spoke seen. Should 
this fail to make the wheel look uniform, in- 
crease the strength of your cylinder until you 
find the weakest that will make the wheel look 
equal in density in all its spokes. When you 
have done this, draw the patient's attention to 
the reading chart, and gradually reduce the 
strength of your plus sphere while it improves 
the distant vision. In other words, the strong- 
est plus sphere combined with the weakest 
minus cylinder that corrected the astigmatism 
is the patient's correction for constant use. 
Myopia. Seat the patient as in the previous 

case. Cover the left eye with the opaque disc, 
ask him to read the smallest type he can with 
the naked eye, record this vision to compare it 
with the final correction. Now place a plus .50 
in the trial frame, and if the patient is myopic 
he will say, "I cannot see so well," or in other 
words, will not be able to read the same line as 
before. Then draw his attention to the astig- 
matic wheel and say, "can you see the spokes 
in the wheel, and do they look equally clear?" 
If he cannot see any of the spokes clearly 
enough to count the lines, remove a quarter D. 
of the plus sphere. If with this he fails to see 
any of the spokes clearly, remove the other 
quarter from the trial frame. If none of the 
spokes are yet clear, begin with the weakest 
minus sphere and gradually increase same a 
quarter D. at a time until one or more spokes 
come up clearly. If they all appear clear at the 
same time there is no astigmatism, and we turn 
to the reading chart and give him the weakest 
minus sphere that will allow him to read the 
best. This would be his correction. On the 
other hand, if there is astigmatism, the wheel 
will not come up equally clear, but some spokes 
will be plainer than others. The main point is 
not to increase the minus sphere after one or 
more spokes appear clearly; for instance, wie 
will say we have on a minus 1 sphere and the 
patient tells us that he cannot count any lines 
in any of the spokes as yet. We add to this 
sphere a minus .25, which will make it minus 
1.25, and if he says "Now I can see one spoke 
clearly," and it runs from 12 to 6. this is the 
time to begin with the weakest minus cylinder. 


placing the axis at right angles to the plain 
spoke, increasing its strength until you find the 
weakest that makes the wheel look uniform in 
density. In this case we will say that it re- 
quired a minus .75 cylinder, that cylinder com- 
bined with the sphere already in the frame will 
be the correction, which will read as follows: 
— 1.25 sph.Q— -75 cyl. ax. 180. 

Triangfe (tri'-ang-gl). (L. tres = three -f angulus 
= angle.) A three-sided plane figure. 

Trichiasis (trick-i'-a-sis). (Gr. thrix = hair.) That 
condition where the eyelashes, instead of ex- 
tending forward, are directed more or less back- 
ward, so as to come in contact with the cornea. 
Trichiasis causes a continual irritation of the 
eyeball, due to the action of the cilia (eye- 
lashes) ; there is photophobia, lachrymation, 
and a constant sense of a foreign body in the 
eye. The cornea itself suffers considerable 

Trichitis (trick-i'-tis). (Gr. thrix = hair + itis = 
inflammation.) Inflammation of the root of the 

Trichosis (tri-ko'-sis). (Gr. thrix = hair.) A dis- 
ease of the hair. See Trichiasis. 

Trichroic (tri-kro'-lk). (Gr. trichroos = three col- 
ored.) That which exhibits three different 
colors in three dilTerent positions. 

Trichromatic (tri-kro-mat'-ik). (Gr. tri = three 
^- chroma = color.) That which has three 

Trigeminus (trl-jem'-in-us). (L. tri = three -f 
geniinus = double.) T. Nerve, also known as the 
fifth, or trifacial, is the largest cranial nerve. 

It has two roots, motor and sensor; it is the 
sensory nerve of the head and face and motor 
nerve of the muscles of mastication. It is a 
branch of this nerve that forms the ophthalmic. 
(See Nerve.) 

Trigonometry (trig-o-nom'-e-try). (Gr, triangle -i- 
metry.) That branch of mathematics which 
treats of the relations of the sides and angles 
of triangles with the methods of deducing from 
certain given parts other required parts and 
also of the general relations which exist be- 
tween the trigonometrical functions of arcs or 
angles. Plane trigonometry and spherical 
trigonometry are those branches of trigonometry 
in which its principles are applied to plane 
triangles and spherical. 

Triplet. (Gr. tri = three.) A combination of 
three lenses. 

Triplopia. (Gr. triploos = triple + ops = eye.) A 
visual defect in which three images are seen 
of the one object. 

Trochlea (troch'-le-ah). (L. pulley.) A pulley- 
shaped part, such as that through which the 
superior oblique muscle passes. 

Trochlearis (troch-le-a'-ris). That which refers to 
the superior oblique muscle. 

Tropom'eter. (Gr. trope = a turning -f metron =^ 
measure.) An instrument for measuring the 
movements of the eye. 

Tumor (tu'mor). (L. tumere = to swell.) A 
swelling. A growth of new tissue, differing in 
structure from the part on which it grows, not 
the result of inflammation. 


Tunic. (L. tunica = coat.) A name given to dif- 
ferent membranes, which envelop organs; the 
eye has three tunics from without inward; first 
the sclerotic and cornea; second, choroid, cil- 
iary body and iris combined; third, the retina 
which is the only one sensitive to light. 

Tunica. Same as tunic. T. adnata, that portion of 
the conjunctiva which comes in contact with 
the eyeball. 

Tutam'ina Oculi. (L. tutamen = a protection.) 
The protecting appendages of the eye, such as 
the eyelids and lashes. 

Tylosis (ty-lo'-sis). (Gr. "knot" + suffix osis = 
condition.) A thickened, ulcerated condition of 
the lid margins after ulceration. 

Typhlorogy. (Gr. typhlos = blind + logia = dis- 
course.) A treatise on blindness. 

Typlilo'sis. (Gr. typhlos = blind + osis = condi- 
tion.) Blindness. 

U LCER. (L. ulcus.) An open sore, other than 
a wound. 

Ulceration (ui-ser-a'-shun). Formation of an ulcer. 

Umbo (um'-bo). (L. prominence.) The apex, 
pointed or protuberant part of any substance. 
When applied to lenses, the extreme elevation 
of a convex spherical lens, or it may apply to 
the center of a concave spherical lens. 

Umbra. (L. umbra = a shadow.) A shadow. 

Undula'tion. (L. unda = wave.) A wave-like mo- 
tion in any medium. 

Un'dulatory Theory. A theory that light, heat 
and electricity move with a wave-like motion. 

Uniaxial (u-ne-ak'-se-al). (L. unus = one.) That 
which has but one axis. 

Unioc'ular. (L. unus = one + oculus = eye.) Only 
one eye. 

Unit (u'-nit). (L. unus = one.) Any standard 
quantity by the representation and subdivision 
of which any other quantity of the same kind is 

Uremia (u-re'-me-ah), (Gr, "urine" + haima = 
blood.) Blood poisoning from retained urinary 

Uvaeformis (u-ve-for'-mis). (L. uva = grape -f- 
forma = form.) The middle coat of the choroid. 

Uvea. (L. uva ^ grape.) The choroid, ciliary 
body, and iris together. 

Uveal (u'-ve-al). That which refers to the vascu- 
lar layer of the choroid coat, or the ciliary body 
and iris. 

Uveal Coat. The second tunic or coat of the eye- 

Uveitis (u-ve-i'-tis). (L. uva = grape -f itis = in- 
flammation.) That condition in which the uvea 
is inflamed. Iritis. 


• Abbreviation for vision. 

Vein. (L. venio = I proceed.) The blood-vessels 

which convey blood toward the heart. They 

are found wherever there are arteries. Veins 

have three coats like the arteries, but they are 


not SO thick. The veins draining the eyeball 
correspond in their arrangement to that of the 
arteries, the main groups being the retinal, 
anterior and posterior ciliary veins. The venae 
vorticosae, collects the blood from the choroid, 
ciliary body, and the iris and pierces the 
sclerotic coat near its equator as four large 
trunks about equal distance from one another, 
where it is joined by the episcleral veins. The 
anterior ciliary veins receive the blood from the 
ciliary muscle and Schlemm's Canal, and after 
emerging from the sclerotic coat it receives as 
tributaries the episcleral and vessels from the 
conjunctiva. These veins upon emerging from 
the eye unite with the other veins from mus- 
cles and tissue to form two main trunks, the 
superior and inferior ophthalmic, which run 
along the roof and floor of orbit to terminate 
in the cavernous sinus. The ophthalmic vein 
joins the internal angular vein (facial) at the 
inner and outer angle of the orbit, thus escaping 
from the orbit in either direction. The inferior 
ophthalmia vein arises in the veins of the eye- 
lids and lacrimal sac, it also receives the veins 
from the floor of the orbit and passes out 
through the sphenoidal fissure. 

Velocity. (L. velocitas, from velox = swift.) 
Quickness of motion. 

Venae Vortico'sae ("a whirlpool"). The veins 
which principally form the external or venous 
layer of the choroid coat (second tunic) of the 
eye; so called from their peculiar arrangement, 
four of them passing out about halfway back. 

Ventricle (ven'-tri-kl). A small belly-like cavity, 
as the two inferior cavities of the heart and 

various cavities in the brain, of which there are 
five in number, namely, the two lateral, the 
third, fourth and fifth. The lateral ventricles 
are the cavities of each half of the cerebrum. 
The third ventricle is between the optic thalami 
at the base of the brain. The fourth V. is the 
space between the cerebellum and the medulla 
oblongata. Fifth V. is in the septum lucidum. 

Vertex (ver-teks). (L. vertex = top from vertere 
= to turn.) A turning point; the principal or 
highest point; top; summit. The point in any 
figure opposite to, and farthest from, the 
base; the terminating point of some particular 
line or lines in a figure or a curve: vertex of 
a curve is the point in which the axis of the 
curve intersects it. Vertex of an angle is the 
point in which the sides of the angle meet. 
A^'ertex of a solid or of a surface of revolution 
is the point in which the axis pierces the 

Vertical. Situated at the vertex or highest point. 
Vertical line is a line perpendicular to the hori- 
zon. Vertical plane. A plane passing through 
the vertex of a cone, and through its axis. (See 

Virtual Focus. (L. virtus — power + "the hearth.") 
An imaginary or negative focus. 

Visibility (vis-i-bil'-i-ty). That which has the ca- 
pacity of being seen. 

Vision. (L. videre = to see.) The ability of the 
organ of sight (the eye) to recognize surround- 
ing objects. Double v., see Diplopia. Binocular 
v., seeing an object with both eyes at the same 


time without diplopia. Monocular v., the act ot 
seeing with only one eye. 

Visual. Pertaining to vision or sight. V. Angle, 
an angle formed by lines drawn from the ex- 
treme edges of an object which cross at the 
nodal point. V. Axis, a line drawn from the 
macula lutea through the nodal point to the ob- 
ject looked at. V. Field, the space containing 
all objects visible while the eye is in a fixed 
position. V. Purple, purple pigment to be found 
in the retina, which is bleached by the action 
of light. 

Visual Acuteness. The amount seen by the naked 
eye if emmetropic; if ametropic, while wearing 
his correction. The smaller the objects that 
the eye can distinguish, or the greater the dis- 
tance at which an object of given size can be 
seen, the greater is the acuity of vision the eye 

Vitreous (vit'-re-ous). (L. vitrum = glass.) A 
transparent fluid occupying the posterior and 
interior four-fifths of the eye. 

Vitreous Humor. (L. vitrum = glass + humere = 
to be moist.) A transparent, colorless, gela- 
tinous mass which fills the posterior cavity, 
four-fifths of the eye. It somewhat resembles 
the white of an egg and is surrounded by the 
hyaloid membrane. See Anatomy. Its index 
of refraction is 1.33. 

Volume (vol'-um). (L. volvere = to roll around.) 
Solid contents. 

Von Graefe's Sign. That condition where the lid 
fails to move downward with eyeball in exoph- 
thalmic goiter. 


ALL-EYE. This term has several meanings. 
It generally refers to white opacities of the cor- 
nea or a pale blue iris. Sometimes divergent 

Wave Theory. The theory that light travels in 
waves instead of rays. See Light. 

Wink. The act of opening and closing the eyelid 

Winker. See Eyelash. 

Worsted Test. The common test employed for 


ANTHELASMA (zan-thel-as'-mah). (Gr. xan- 
thos = yellow + elasma == a beaten metal plate.) 
That condition in which there is a flat tumor of 
a dirty sulphur-yellow color which projects a 
little above the skin of the lid. It is found 
most frequently on the upper and lower lids at 
the inner angle of the eye. 

Xanthocyanopla (zan-tho-cy-an-o'-pi-ah). (Gr. xan- 
thos = yellow + kyanos = blue + ops = eye.) 
That condition in which there is an inability to 
perceive red and green colors. 

Xanthoma (zan-tho'-mah). (Gr. xanthos = yellow.) 
A yellowish new growth on the skin. 

Xanthophane. (Gr. xanthos = yellow.) A condi- 
tion in which objects appear yellow. 

Xeroma (ze-ro'-mah). (Gr. xeroa = dry.) That 
condition where the conjunctiva is abnormally 

< il'JIIllAL.MH' DK'IIONAKV 2T.'. 

Xerophthalmia ( zo-rof-thar-nii-ah ). (CIr. xeros — 
dry + ophthalmos ^- eye.) Conjunctivitis with 
atrophy and no liquid discharge. 

Xerosis (ze-ro'-sis). (Or. xeros = dry.) Abnormal 

dryness of the eye. 

1 ELLOW SPOT. The macula lutea. 
Young-Helmholtz Theory of Color Blindness. 
rrhoniiis Young, English physicist, 1773-lS:ii>; 
Herman Ludwig Helmholtz, German physicist. 
1821-1894.) The theory that color vision de- 
pends on three sets of retinal fibers which cor- 
respond to the colors red. violet and green. 

#jEISS"S GLANDS. The sebaceous or sweat 
i; lauds locaird al the free border of the eyelids. 

Zinn's Ligament. (Johann Gottfried Zinn, German 
anatomist, 1727-1759.) A circular ligament at 
the optic foramen from which arises the recti 
muscles of the eye; the ligament itself is at- 
tached to the bone and allows the optic nerve 
to pass through its center. 

Zone. (L. girdle.) A girdle or belt. 

Zonula. A very small membrane surrounding a 
body. A small zone. 

Zonule of Zinn. The suspensory ligaments of the 
t^ye-lens form the Zone of Zinn. It consists of 
delicate fibers which take their origin from the 
inner surface of the ciliary body, beginning at 
the ora serrata. The fibers are in contact with 
the surface of the ciliary body, but leave it at 

the apices of the ciliary processes, and, becom- 
ing free, divide and pass over to the edge of the 
lens, thus forming the anterior and posterior 
suspensory ligaments. These ligaments are at- 
tached to the capsule of the lens with which 
they become fused. The space, triangular in 
shape, included between the fibers of the zonule 
or suspensory ligaments and the edge of the 
lens is called the Canal of Petit. 

Just outside of the optic nerve, where it 
pierces the eyeball, is found a circle of blood- 
vessels giving a free supply to the optic sheath 
at this point, and sending branches into the 
substance of the nerve to supply nutrition. This 
circle is known as the Circulus of Zinn or some- 
times called a Zone of Zinn. 
Zonulitis. (L. zonula + Gr. itis.) Inflammation 
of the zonule of Zinn. 



1. Q. What governs the passage of light through 

any transparent media? 
A. Density. 

2. Q. On what does the visual angle depend for 

its existence? 
A. The size and distance of the object. 

3. Q. What three laws accompany refraction? 
A. Reflection, absorption and dispersion. 

4. Q. In what three ways can an incident ray be 

disposed of? 
A. Reflected, absorbed or refracted. 

5. Q. What three laws must be brought into play 

in order to obtain distinct binocular vision 
at various distances? 
A. Refraction, accommodation and converg- 

6. Q. Why is it necessary for the aqueous humor 

to be thinner than the vitreous humor and 
yet have the same density? 
A. To allow freedom of movement to the iris. 

7. Q. Why is accommodation and convergence so 

closely associated? 
A. Because they are both operated by the 
same nerve. 

8. Q. What lens represents the focal strength of 

the dioptric system of the eye? 
A. From 62 to 65-D. plus. 

9. Q. vVhen is a lens periscopic? 

A. When it is minus on one side and plus on 
the other. 
10. Q. What are objective and subjective symp- 

A. Objective symptoms are what the operator 
detects without questioning the patient. 

Subjective symptoms are those described 
by the patient. 

11. Q. Why does Astigmatism in one eye some- 

times cause convergent Strabismus? 
A, In order to prevent the eye Avith the 
blurred vision interfering with the vision 
of tlie good eye the patient learns to turn 
it toward the nose. 

12. Q. Why do we add and subtract from retino- 

scopic findings? 
A. To place the patient's far point at 20 feet. 

13. Q. Why is the concave retinoscope superior 

to the plane? 
A. Because a concave retinoscope combined 
with a plus 20-D. lens can be used as an 

14. Q. What lens can be combined with plus 2 

sphere combined with plus 1 cylinder, axis 
90, that will increase the cylinder and de- 
crease the sphere? 
A. Any minus cylinder under 2 dioptrics with 
its axis at 180. 

15. Q. What is false myopia, and how is it pro- 

A. A spasm of accommodation in emmetropia 

will cause the eye to appear myopic, and is 

brought about by continual strain at close 

work, exophoria or hyperopia. 
Ifi. Q. Is an Ophthalmic lens used to improve 

A. No. The lens is to refract the light only, 

which sometimes brings the focus nearer 

to the retina resulting in better vision. 
17. Q. Could Strabismus exist and <he eyes be 



A. Yes. The deviation may be due to Hyper- 
metropia or abnormal vision in one eye 

18. Q. Can an eye be parallel with its fellow while 

wearing a single prism? 
A. Not unless the Macula Lutea is displaced. 

19. Q. Do prisms make eyes parallel in Hetero- 

A. No. They allow them to deviate from 

20. Q. Name three things that would interfere 

with the action of accommodation. 
A. Paralysis, hardening of the lens, loss of 
Crystalline Lens. 

21. Q. What three things determine the focal 

length of a lens? 
A. Curvature, density and distance of object. 

22. Q. What is a prism diopter? 

A. The power of a prism to deviate a ray of 
light one centimeter in a meter. 

23. Q. What are the constituents of Crown Glass? 
A. Crown glass is so called from the trade- 
mark by the early manufacturers. It is 
composed of lime, sand and soda. 

24. Q. What is the composition of Flint Glass? 

, A. Somewhat like Crown only less sand and 
lead is used to increase its density. 

25. Q. Which is the harder, flint or crown glass? 
A. Crown glass is about 20 per cent harder^ 

because it has no lead and more sand. 

26. Q. Which has the most dispersive power, flint 

or crown? 
A. Flint has the most dispersive power, be- 
cause of its higher index of refraction. 


27. Q. Transpose the following Rx.: 

— 1. cyl. ax. 20 
—2. sph.+2.50 cyl. ax. 180 
4- .50 sph. + l cyl. ax. 60 
A. — 1 spli. -f 1 cyl. ax. 110 
+.50 sph. — 2.50 cyl. ax. 90 
— 1.50 sph. — 1 cyl. ax. 150 

28. Q. TMiat errors of refraction will the above 

prescriptions correct? 
A. (a) Simple myopic astigmatism, (b) Mixed 
astigmatism, (c) Compound hypermetropic. 

29. Q. What vision does an emmetropic eye al- 

ways have? 
A. Emmetropia has no reference whatever to 
vision, but we expect normal. 

30. Q. Does a hypermetropic eye ever have nor- 

mal vision? 
A. Yes. Provided he is able to overcome his 
error by accommodating. 

31. Q. Name four reasons why vision would not be 

A. Cataract. Focus off the retina. Amblyopia. 

32. Q. If an object is 80 inches from a -f 3 sphere 

where will the image be? 
A. 16 inches. 

33. Q. If an eye looking 20 feet away sees as well 

without as with a +2 sph. should it be worn? 
Give reason for your answer. 
A. Yes. It shows relaxation from accommo- 

34. Q. In correcting astigmatism where would you 

place the axis of the cylinder, if the spoke 
from 11 to 5 was seen the blackest? 
A. 150 degrees. 

:>J» Q WhAi orrv^r of ivtYaction wouKI vou c-^uso 

And \vouK1 it bo with or ajiainsst tho rulo if 

you plaoi?d a -f 1 Ql- a^ lJ^<^ K>foro an onv 

motropiv-* ove? 

A iNinipIo Myopio a^tiiimatisim. With tho ruU\ 

;>ti. Q rvv>n what i:^ tho doviatin>: innver vM' a 
V^rism dopondont ? 
A. The pv^wor of pri;?m is doptnidont upon its 
«ui|rlo and its indox of ivtYaotion. 

*^T, Q What is a ov>mpvnim1 lens? 

A, A Ions made with a spherical and cylin- 
drioal effoot, also known as a sv^heiwoyl^ 

C>S, Q What IS tho kind of iilass tYoni which or- 
dinary spootaolo lenses are madet What 
is its index t 
A, It is Crown Glass Index varies t>i"»m 1 50 
to 1 5:V 

Si*, Q What does myosis with photophobia in nor- 
mal lij:ht indicate t 
A, Myosis in normal lijtht with photophobia 
indicates a serious disease, as a nile. 

40, Q What is the first thiiv.^ to do in making an 
A >Cxamine for diseased conditions befortMVir- 
rectins errors of refraction. 

41 How would you prove a pair of eyes has 
cxophoria that roiiuin^s a prismatic correc- 
tion for constant wear* 
A, If after the patient has worn his distjtnt 
correctio>n for the ametrt^pia a few weeks 
the muscle trouble remains, 1 would tvciire 
to correct the trouble With the maddox 
Tv»d horizontal before the ri»;ht eye and the 
rt>d glass befort^ the left, the jvitient will 


see the red light to the right of streak, and 
it would require prisms base in to bring 
them together, proving exophoria. 

Points one should be familiar with before attempt- 
ing a State Examination: 

1. Mechanical parts of frames and guards for 
mounting lenses; making face measurements 
for same; truing up bent frames and guards; 
adjusting same to different persons. 

2. The common shapes and forms and diop- 
tric values of lenses of different kinds; sub- 
mitting ten different kinds to applicants for 
determination of these qualities. 

3. Practical fitting with trial case, a test of 
the applicant's practical ability to go through 
these tests and accurately fit different classes 
of cases with lenses. 

4. Shadow testing, with or without stand in- 
strument; the actual doing of this work and 
determining the error of refraction by the 
method. The mirror or instrument preferred 
may be used, 

5. Muscle testing, and the use of muscle test- 
ing devices; a test of the applicant's ability to 
make these tests and draw correct conclusions 
from them and their showings. 

6. The proper use of different optical instru- 
ments used to measure the refraction of the 
eyes or any surface, or the power of the mus- 
cles of the eyes. 

7. Questions on the anatomy and physiology 
of the eyes, including muscles, nerves, tissues 
and their functions. 

8. Questions on retraction of lenses, transpo- 
sition, conjugate foci, image forming, and the 
media of the eye. 



1. Name the extrinsic and intrinsic muscles of 
the eye. 

2. Describe the Iris, the muscles that control its 
movements and the mechanism that causes the 
pupil to contract and expand, what causes the 
movements and how they assist in procuring clear 

3. Describe the humors of the eye and why it is 
desirable that a certain humor be more fluid than 
the others. 

4. Describe the Choroid and its functions. 

5. Describe the Crystallme Lens. What holds 
it in position? What controls and alters its sh^pe? 
What is its index of refraction? What is its 
strength in diopters and how does it assist in 
procuring good vision? 

6. Describe the Optic Nerve and Retina and 
their functions. 

7. Is the human eye chromatic or achromatic? 
How can it be proven? 

8. Describe the Conjunctiva and its office. 

9. Which part of the eye has the greatest re- 
fracting power? Why? 

10. Describe the eyelids, eyebrows, eyelashes 
and the office of each. 

11. Describe the Lachrymal Gland and its ap- 
pendages and their office, 

12. In which part of the brain are the optic cen- 
ters situated? 

13. Describe the principal veins and arteries of 
the eye. 

14. Prom what source does the Cornea receive 
its supply of nourishment? 

15. What is meant by abduction? Adduction? 


Sursumduction? Torsion? Name the muscles that 
produce them. 

16. Define visual angle; minimum visual angle; 
visual acuity. 

17. What is Pterygium? Trachoma? Nystag- 
mus? Keratitis? 

18. Explain the Helmholts and Tscherning the- 
ories of accommodation. Which, in your opinion, 
is more reasonable? Why? 

19. What do you understand by Co-ordinate 
movements of the eye? 

20. Make a diagram of an eye, showing the 
principal parts, briefly describing the functions of 
eaoh part. 


1. Explain what is meant by the Conjugace 
movements of the eyes. 

2. What is the retractive condition and ampli- 
tude of accommodation of a person whose P. R. 
with a plus 5 D. Sphere is 50 C. M. and whose 
P. P. with a plus 2 D. Sphere is 10 C. M.? 

3. What is the usual size of the ocular pupil in 
uncorrected ametropes who do not complain of 

4. A person has a fixed deviation outward of 
one eye of 4 meter angles. What prism will cause 
the images to fuse at 50 C. M.? Where would you 
place the base of the prism? 

5. Describe fully your method of measuring the 
relative strength of the extrinsic muscles of the 

6. Give the rule for the prism diopral decentra- 
tion of lenses, and work the following problem by 
it: A pair of plus 3 D. S. are decentered 5 mm. 
inward. How much prism value results? 


7. Give the rule for transposing plus spheres 
I combined with plus Cyl's to plus Sph. combined 

with minus Cyl's and work the following by it 
(leaving your figures on the paper): (a) Plus 1.75 
D. S. combined with plus .75 D. C, axis 15. (b) Plus 
1.25 D. S. combined with plus 1.50 D. Cyl. axis 135. 

8. Give the rule for transposing cross Cyl's into 
Sphero Cyl, and work the following by it, leaving 
your figures: (a) Plus 1 D. C. axis 90 combined 
with a plus 2 D. C. axis 180. (b) Plus 1.25 D. C. 
axis 90 combined with a minus .50 D. C. axis 180. 

9. In Retinoscopy what is the nature of the 
refraction of the eye under observation when one 
point of reversal is found at 20 inches and another 
at 40 inches? 

10. A coin one inch in diameter is held 12 inches 
from a lens, the principal focus of which is 4 
inches. Where will the image be formed? 

11. Explain the relation existing between accom- 
modation and convergence. 

12. Explain the principles governing the use of 
the Ophthalmometer and its practical working. 
To what extent can it be relied upon as a means 
of estimating refractive errors? 

13. A child of 10 years who has never worn 
glasses is found to have 4 D. of hyperopia and 
esophoria of 5 degrees. Would you order prisms 
or decenter the lenses in this case? 

14. A certain prescription reads plus 1 D. S. 
combined with plus 1.25 D. C. axis 90. Give the 
dioptric value of the surfaces of the lens. 

15. Define Anisometropia; Asthenopia; Amblyo- 
pia; Orthophoria. 

16. With the static method and the retinoscope 
at 40 inches the shadow is neutral with a plus Z 


Sphere before the observed eye. What two points 
are conjugate and what is correction for that eye? 

17. In static skiametry with plane mirror at 26 
inches and a plus 1.50 D. S. in rear cell of trial 
frame no movement is found in the horizontal 
meridian and a plus .75 Sph. neutralizes motion 
in the vertical meridian. What direction had the 
shadow before the plus .75 D. S. was used? What 
kind and amount of ametropia was indicated? 

18. A boy of 14 years has vision equal to 20-15 
without glasses. Would you accept that as proof 
of emmetropia? Give your reasons. 

19. If double concave lens could be made of air 
with its radius of curvature 20 inches for each 
side, what would be the nature of its refraction if 
it were immersed in water and what would be its 
action on parallel rays of light? 

20. If a person 15 years of age should come to 
you to have a complete examination of the eyes, 
how would you proceed? What questions would 
you ask and how would you proceed to make the 
examination, together with the record you would 
make? Give full particulars just as if you had 
such a case. 


1. What is light? How does it travel from a 
luminous pomt? What three things may happen 
to it when it comes in contact with another 

2. What is reflection? Give the law governing 
incident and reflected rays. If a ray is incident 
at an angle of 30 degrees, at what angle will it be 

3. The radius of curvature of a concave mirror 
is 16 inches. What will be its principal focus? 


If a candle is placed 12 inches in front of it, at 
what distance will its image be formed? 

4. What is refraction? Make a diagram sliow- 
ing the path of a ray of light as it strikes the 
surface of a plate of glass, as it passes through. 
and after it emerges. What are the three parts 
of the ray called? 

5. What is meant by the term "surface power 
of a lens"? A certain lens has a surface power of 
plus 6.25 D. S. on one side and on the other minus 
1.25 D. S. What curvatures must a cement seg- 
ment have to make the reading portion plus 6 D. 
when the index of refraction is the same in both 
parts of the lens? 

6. Make diagram showing three double convex 
lenses and, the course of parallel rays of light 
through them, the principal focus, the secondary 
focus, and one pair of conjugate foci. 

7. A plus 2.50 D. S. is held 30 inches from a 
candle. Where will the image be formed? 

8. The light from a candle passes through a 
plus 3 D. S. at 50 C. M. Where should a screen 
be placed to get the best defined image? Show 
your method of working this problem. 

9. A certain lens focuses parallel rays of light 
at 20 C. M. What lens must be placed in front of 
it t© send the focus back to one meter? 

10. What is meant by "the power of a prism"? 
If you had two weak prisms and desired to know 
their powers within one per cent, what method 
would you (Miiploy and how would you proceed to 
carry out the measurement? 

11. Describe how bifocal lenses should be ad- 
justed and the position which the reading portion 
should occupy. 


12. A plus 1.50 D. piano Cyl is placed in contact 
with a similar one of plus .75 D.; axis right angles. 
What Is the resultant combination? 

13. If you desired to find the power of a double 
concave lens and had no lens measure or neutral- 
izing lenses, how would you proceed if the index 
of refraction of the glass was 1.50? 

14. Give the rule for transposing plus spheres 
combined with minus Cyls and work the following 
by it: Plus 3 D. S. combined with minus 1.25 
D. C. axis 45. Plus 2 D. S. combined with minus 
2.50 D. C. axis 65. 

15. Transpose the following: 

Plus 3.50 D. S. plus 1.25 D. C. axis 135. 
Plus 2 D. S. plus D. C. axis 65. 
Minus 3 D. C. minus 2 D. C. axis 75. 
Minus 2 D. S. minus 3.25 D. C. axis 155. 
Plus 2.25 D. C. axis 90 plus 150 D. C. axis 180. 
Minus 2.25 D. S. plus 175 D. C. axis 135. 

16. What error will the following prescription 
correct: R. plus 1 D. S. minus .75 D. C. axis 180, 
combined with 2 degree prism base up. 

17. Describe Glaucoma. Trachoma, Pterygium. 
Cataract. Granulated lids. 

18. What is Ophthalmia Neonatorum? What 
simple method will prevent it? 

19. Describe the fogging method of measuring 
refraction and your everyday manner of apply- 
ing it. 

20. A young person complains of Asthenopia 
and the third trial case shows Myopia of 1.25 D. 
The Retinoscope shows 1.50 of Hyperopia. What 
would you give in the way of lenses? Why would 
you give them?