James John Lewis.

Pocket optical dictionary, including pronunciation and definition of the principal words used in optometry and ophthalmology, together with a complete description of the light wave theory, anatomy of online

. (page 1 of 12)
Online LibraryJames John LewisPocket optical dictionary, including pronunciation and definition of the principal words used in optometry and ophthalmology, together with a complete description of the light wave theory, anatomy of → online text (page 1 of 12)
Font size
QR-code for this ebook

Optical Dictionary










Optical Dictionary


Pronunciation and Definition


Optometry and Oplitkalmology

Together with a complete description
of the light wave theory, Anatomy of
the Eye, functions and nerve supply
of the different parts, Retinoscope,
Ophthalmoscope, Trial Case and how
to use them. Transposition, Toric
and other lenses.


Professor of Optometry in the Northern Illinois College ol
Ophthalmology and Otology.

Revised and Enlarged Illustrated

Copyrigkt, J. J. LEWIS



To the Public:

This edition has been compiled with a
great deal of care. Realizing that perfection
in its full sense hasi 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 optome-

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 Author.





^ P < The second edition of this work has met
with so much favor, that the Author has
attempted to revise it, and in this way make
it more worthy of the commendation of the
profession. Many definitions have been re-
written, and about twenty pages of new
matter has been added in the form of an

I wish to express my appreciation for the
efficient assistance extended by

J. B. McFatrich, M. S., M. D.,

Professor of the Principles of Ophthalmology

and Otology.

Geo. Wilbur McFatrich, M. D.,

Professor of Clinical and Didactic Ophthalmology
and Otology.

Henry S. Tucker, A. M., M. D.,

Professor of Anatomy and Physiology of the Eye
and Brain.

I particularly acknowledge the assistance
of my friend. Dr. G. W. McFatrich, whose
knowledge, gained through experience as Pro-
fessor of Ophthalmology in Medical Colleges
and as Oculist to Hospitals in Chicago and
large professional practice in Diseases of .
the Eye, has been freely placed at my com-
mand in bringing this little book to the
highest possible standard.

J. J. Jm


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 Diopter.

D. Cc Double concave.

D. Cx Double convex.

D. T Distance test.

E or Em Emmetropia.

H. or Hy Hypermetropia.

In Inches.

L. or L. E Left eye.

M. or My Myopia.

Mm Millimeter.

N Nasal.

N V 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 concave.

P. Cx. Periscopic convex.

P. D. . . . , ♦ t , , , , , , 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.

Va Visual acuteness.

W. P Working point.

+ Plus convex.

— Minus — concave.

O Combined with.

^ Degree.

A Prism Diopter.

= .^ Equal to.

00 Infinity, 20 ft. or farther.

'-" Line, 12th part of inch.

Should the word not be found in alphabetical order
refer to the appendix.

When this sign * is found at the end of a definition.
refer to the same word in the appendix.

Lewis Pocket Optical Dictionary.

A-baxial (ab-aks'-e-al). Not situate in the line of
the axis.

Abducens (ab-du'-senz). Refers to the sixth pair of
nerves that control the movement of the external
rectus muscles. They are the straight muscles,
sometimes called the abducens muscles, located
on the temple side of the eyeball, which turn the
eye outward, and under normal conditions these
muscles should overcome about 8 degrees of
prism, base in.

Abduct. To draw away from the median line.

Abduction (ab-duc'-shun). The act of turning the
eye outward. For testing the power of the ab-
ductors or external recti muscles, use the strong-
est prism, base in, with which the eye can over-
come diplopia.

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

Aberration (ab-er-a'-shun). Wandering from nor-
mal. When applied to lenses would mean, unable
to obtain a perfect focus. It is due to the greater
refractive power of the edge over the center of
convex lenses, thus causing the image to be some-
what 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 distanc \


Ablatio-retinae (ab-la'-she-o-ret'-in-e). Detachment
of the retina.

Ablepharia (ah-blef-ar'-e-ah). That condition in
which the eyeHds are absent.

Ablepsia (ah-blep'-se-ah). BUndness — want of sight

Abnormal. Away from normal. Relating to vision
would mean, any defect of sight. (Ametro-
pia.) An eye wherein parallel rays of light do
not focus on the retina with the muscles of accom-
modation at rest.

Abrasio-cornea (ab-ra'-sio-cor'-ne-ah) . The rub-
bing off of the outer layer of the cornea.

Abscess (ab'-ses). A collection of pus in any cavity
formed by the separation of tissue.

Absolute Index of Refraction is that which is found
when light passes from a vacuum into a given

Absorption (ab-sorp'-shun) . 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-

V Accommodation. The power to adjust the eye to
see within its far point. It takes place by con-
tracting the ciliary muscles which encircle the
lens and draws forward the choroid and hyaloid
membrane, the suspensory ligaments be-
coming relaxed, and the lens (by its own elas-
ticity) allowed to as.^ume a greater convexity,



especially its anterior surface, thus increasing its
refraction. Amplitude of Accommodation (from
Landolt) as follows:

Age in Amplitude

Years (dioptres)

10 14

15 12

20 10

25 8.5/

30.. 7.0

35 5.5

40 4.5

45 3.5

50 2.5

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.

Achroma. Without color.

Achromatic Lens (ah-kro-matMk). (See Lens.)

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

Achromatopsia (ah-kro-mat-op'-se-ah). Color-blind-

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

Acorea (ah-ko'-re-ah). When the pupil is absent.
Acouired. Ngt hQvn with, but developed after birth,


f Acuity (ak-u'-it-e). Sharpness, like a needle. The
sharpness of vision; the keenness of the visual
powers. The acuteness of vision means the vision
the patient has with his full correction. The
faculty of the retina to perceive forms depends
on many conditions —

1. Primarily, 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 image.

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-ap-ta'-shun). Adjustment of the
pupil to light.

Adducens (ad-du'-sens). When this term is applied
to the eye it means the internal rectus muscle,
the muscle which turns the eyeball inward toward
the nose. The power of adduction of the eye
ranges from twenty up to fifty degrees. For
testing the power of the adducens or internal
rectus muscle, use the strongest prism, base out,
with which the eyes can overcome diplopia.


Adduct. To draw inward toward a center.

Adduction. Movement of the eyeball inward. 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 placing the


base out of the strongest prism with which the eyes
can overcome diplopia.

Adenectomy (ad-en-ek'-to-me). Removal of a gland
by operation.

Adenemphraxis. That condition in which the duct
or gland is obstructed.

Adenoid (ad'-en-oid). Resembling a gland.

Adenophthalmia (ad-en-off-thal'-me-ah) . Inflam-
mation of the meibomian glands.

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-

Albinism (al'-bin-ism). Abnormal deficiency of pig-
ment in the iris and choroid.

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

Alexia (a-lex'-ia). Unable to read, due to a central

Amaurosis (am-aw-ro'-sis). A disease of the optic
nerve or retina, which causes blindness.

"^ Ambiopia (am-be-o'-pe-ah). Vision with both eyes.

. Amblyopia (am-ble-o'-pe-ah). A dimness of vision
^ from defective sensibility of the retina. A
condition in which there is a possibility of re-
storing 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 the 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 diopters apart in-
struct 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 way you will
notice an improvement each week. When the
pinhole disc fails to improve vision, the eye is
either amblyopic or in a diseased state. Toxic
Amblyopia is a dimness of vision from the poison-
ous effect of drugs, such as quinine, upon the
nervous system — excessive use of tobacco or al-
coholic 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 recov-
ering the former vision. A., Postmar'ital, that due
to sexual excess. A., Crossed, on one-half of retina.

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

Ametrometer (a-met-rom'-e-ter) . An instrument
used for measuring ametropia.

V Ametropia (a-met-ro'-pe-ah). Any error of re-
fraction, such as hyperopia, myopia, or astig-
Amphice'lous. Concave on both sides or ends.
Amphodiplopia (am-f o-dip-lo'-pe-ah) . That condi-
.XlQU where both eyes have double vision,


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

Amplitude of Accommodation. The power or force
N necessary to change the eye from its far point
to its near point (or from its punctum remotum
to its punctum proximum). (See Accommo-

Amplitude of Convergence. The power or force
Ny^ necessary to turn the eyes from their far point
to their near point of convergence. It is rep-
resented by the greatest number of meter angles
of convergence that the eyes can exert.

Anacamptom'eter. An instrument for measuring
the reflexes.

Anaclasis (an-akMas-is). When this term is applied
to Hght, it refers to the rays traveling obliquely
from a rarer to a denser media, being bent back-
ward toward the perpendicular (refraction).

Anaesthesia (an-es-the'-ze-ah). Lacking sensitive-
ness, where the retina is amblyopic.

Anatomy (an-at'-o-me) (Eye). Relates to the
description of the structures of the eye and its
parts. The eyeball is nearly spherical in shape and
measures about 24 mm. in diameter. The cornea
represents a segment of a small sphere projecting
from its anterior surface. The first tunic of the
eyeball is the sclerotic and cornea. The posterior
five-sixths is the sclerotic, which is white and
opaque, and serves to 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
sclerotic. The cornea is set in the sclerotic as

a watch 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 cornea,
there are a number of comb-like openings which
are iu the trabecular tissue or pectinate ligament


which runs from the periphery of the 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 cir-
cular canal extending around the periphery of
the cornea at the sclero corneal junction, but
entirely within the cornea. From this canal the
humor passes into the anterior ciliary veins. The
second tunic of the eye is composed of the choroid,
ciliary body and the iris. It lines the inner side
of the sclerotic, and is perforated to allow the
optic nerve to enter, and has a circular opening in
front, which is known as the pupil. Through
this tunic the eye obtains its principal blood and
nerve supply. This is the tunic in which the
pigment is deposited for the purpose of absorbing
light. The choroid is said to nourish the retina
and the vitreous. The ciliary muscles are within
the ciliary body, and are used for accommodating.
The iris is the most anterior portion of the second
tunic. It is located in front of the crystalline
lens, and separates the posterior and anterior
chambers; it gives the eye its color, regulates
the amount of light which enters, and prevents
spherical aberration of the lens. The third tunic
is the retina. It is a very delicate, transparent
membrane, made up of ten layers, one of which is
the layer of optic nerve fibers. These fibers pass
through the lamina cribrosa at the optic disc,
and flatten out more and more 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 ophthalmoscope you will

, Cornea; Scl, Sclerotic; Ch, Choroid; R, Retina; or^ C
Serrata; Z, Zonule of Zinn or Suspensory Ligamen
//, Petit's Canal; p, Edge of Pupil; P, the most promint
part of the Ciliary Process; sp, Sphincter Pupillae Muse
a, Canal of Schlemm; L, Conjunctiva; B, Lens; I, Angle


notice the optic disc on the nasal side which
marks the entrance of the optic nerve into the
globe. The macula lutea, which is the most sen-
sitive 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 functions of the retina are 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 transpar-
ent, 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 substance about the consistency of
the white of an egg, and is enclosed in a thin trans-
parent sac known as the hyaloid membrane. This
membrane divides at the ciliary body and forms
what is known as the anterior and posterior sus-
pensory 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 crystal-
line lens is made up of layers closely resem-
bling 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 membranous sac, which isolates it and at the
same time allows free movement. This sac is
named the Capsule of Tenon. It is a very deli-
cate membrane consisting of two layers which
invest 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, which is known as the subarachnoid
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) muscle,!
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. The orbits are two pyramidal
I cavities, 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 would 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 palate;
but three of these, the frontal, ethnoid, and
sphenoid, enter into the formation of both orbits,



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 circular
opening known as the optic foramen, which trans-
mits the optic nerve and ophthalmic artery.
There are nine openings communicating with
each orbit, viz., the optic foramen, the spheno-
maxillary fissure, sphenoidal fissure, supraorbital
foramen, anterior and posterior ethmoidal for-
amina, infraorbital canal, malar foramina, and
the canal for the nasal duct. Spheno-maxillary
fissure transmits the superior maxillary nerve
and its orbital branches, the infraorbital 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 filaments from the cavern-
ous plexus of the sympathetic, the orbital
branch of the middle meningeal 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 ethnoidal foramen transmits
the anterior ethmoidal vessels and nasal nerve.
Posterior ethmoidal foramen transmits the poste-
rior ethmoidal vessels. Infraorbital canal opens
just below the margin of the orbit. Malar
foramina is a passage for nerves and vessels from
the orbit.

Angle, A figure formed by two straight lines ex-
tending out from one point in different direc-
tions. yAngle Gamma is formed at the center of


rotation of the globe by the optic axis and a line
drawn from the point on the object looked at.
Angle of Convergence is the angle which the two
visual axes form in turning from infinity to a
point less remote. The angle thus formed, when
the two 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 distance, it
is called a two-meter angle of convergence, and
when looking at a third meter distance it is called
a three-meter angle of convergence. V Visual A.
is an angle formed by rays of light coming from
the extremities of an object looked at and cross-
ing at the nodal point of the eye. This angle
depends for its existence upon the size and dis-
tance of the object. A. of Incidence is the angle
formed by the incident ray with the perpendic-
ular. A. of View (same as visual angle). Optic
A. is formed by the meeting of the optic axes of
the two eyes. A. of Reflection is an angle
formed by the reflected ray with a line per-
pendicular to the reflecting surface, and is always
equal to the Angle of Incidence.

s. Angle Alpha (ang'gel al'-fa). The angle formed by
the optic and visual axis.

Angle of Incidence. The angle formed by the inci-
dent ray with the perpendicular.

Angle of Refraction. The angle formed by the re-
fracted ray with the perpendicular.

Anian'thinopsy. Inability to distinguish violet


Aniridia (an-ir-id'-e-ah). Congenital absence of the

Anisocoria (an-is-o-ko'-re-ah). That condition where

the two pupils are unequal.

Anisometropia (an-is-o-me-tro'-pe-ah). A diflfer-
\. ence of refraction in the two eyes. The defect is
usually congenital, but it can be acquired, as in
Aphakia, or operations of any kind. One eye
may be emmetropic, the other hypermetropic, or
myopic, or one more hypermetropic, 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-

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

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

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

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

Anophthalmia (an-off-thal'-me-ah) . Absence of the

Anopsia (an-op'-se-ah) . Disuse of the eye from
certain defects.

Anortkopia (an-or-tho'-pe-ah) . When the eyes are
turned from parallelism. (Strabismus.)

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



Antimetropia (an-ti-me-tro'-pe-ah). Where one eye
is myopic and the other hypermetropic.

Antiseptic (an-ti-sep'-tik). A substance which is
destructive to poisonous germs.

Apex (a'-pex). The thin edge of a prism.

\i Aphakia (ah-fa'-ke-ah). Absence of the crystalline

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

Aplanatic (ah-plan-at'-ik). That condition where
there is neither spherical nor chromatic aberration ,
and the lines are also straight. (See Lens.)

Aponeurosis (ap-on-u-ro'-sis) . The fibrinous ex-
pansion of a tendon.

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

1 3 4 5 6 7 8 9 10 11 12

Online LibraryJames John LewisPocket optical dictionary, including pronunciation and definition of the principal words used in optometry and ophthalmology, together with a complete description of the light wave theory, anatomy of → online text (page 1 of 12)