Optical Dictionary 
 
 AND 
 
 Encyclopedia 
 
 THIRD EDITION 
 
 LEWIS 
 
 REVISED MAY i, 1909 
 
U,C,1PP.EY LIBRARY 
 
imm/ 
 
1^^ 
 
POCKET 
 
 Optical Dictionary 
 
 INCLUDING 
 
 Pronunciation and Definition 
 
 WORDS 
 
 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. 
 
 By JAMES J. LEWIS, Opt. D. 
 
 Professor of Optometry in the Northern Illinois College ol 
 Ophthalmology and Otology. 
 
 THIRD EDITION 
 Revised and Enlarged Illustrated 
 
 Copyrigkt, J. J. LEWIS 
 1908 
 
 M 
 
OPTO 
 
 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- 
 trists. 
 
 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. 
 
bKE 
 
 Z.[ 
 
 PREFACE 
 
 TO THE THIRD EDITION 
 
 ^ 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 
 appendix. 
 
 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 
 
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 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. 
 
ABBREVIATIONS AND OPTICAL SIGNS— Con. 
 
 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 \ 
 
8 LEWIS POCKET 
 
 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 
 medium. 
 
 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- 
 sorption. 
 
 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, 
 
\f 
 
 OPTICAL DICTIONARY. § 
 
 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- 
 ness. 
 
 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, 
 
10 LEWIS POCKET 
 
 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 
 
OPTICAL DICTIONARY. li 
 
 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- 
 mal. 
 
 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 
 lesion. 
 
 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 
 
12 LEWIS POCKET 
 
 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- 
 matism. 
 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, 
 
I OPTICAL DICTIONARY 13 
 
 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- 
 dation.) 
 
 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 
 
14 
 
 LEWIS POCKET 
 
 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 
 
OPTICAL DICTIONARY. 15 
 
 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 
 
A CUT THROUGH THE CILIARY BODY. 
 , 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 
 Filtration. 
 
OPTICAL DICTIONARY. 17 
 
 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 
 
18 LEWIS POCKET 
 
 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, 
 
\' 
 
 OPTICAL DICTIONARY. 19 
 
 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 
 
no LEWIS POCKET 
 
 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 
 shades. 
 
OPTICAL DICTIONARY. 21 
 
 Aniridia (an-ir-id'-e-ah). Congenital absence of the 
 
 iris. 
 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- 
 ness. 
 
 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 
 eyes. 
 
 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. 
 
V 
 
 $9 LEWIS POCKET 
 
 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 
 lens. 
 
 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. 
 
 ^ Appendages of the Eye are the orbits, the eyebrows, 
 the eyelids, the conjunctiva, the lachrymal appar- 
 atus, 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 flattened. 
 
 ^ Aqueous Humor (a'-que-us hu'-mor). A transpar- 
 ent, watery fluid which fills the anterior and. 
 posterior chambers, the iris becoming the boun- 
 dary line between the two chambers. If this 
 humor is allowed to escape it will re-form again. 
 Its index of refraction is 1.33. 
 
 Aquocapsulitis (a'-kwo-caps-u-li'-tis). Serous inflam- 
 mation of the iris. 
 
\ 
 
 OPTICAL DICTIONARY. 23 
 
 Arc. Any part of a curved line. 
 
 Arcus senilis (ar'-kus sen'-il-es). White circle in 
 cornea near sclerotic. Condition in aged. 
 
 Area of Critical Definition. That portion of an 
 optical image within which the detail is clearly 
 defined. 
 
 Argamblyopia (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 accommodation. 
 Can be seen in locomotor-ataxia. 
 
 Artery. The vessel which carries the purified blood 
 from the heart to the different cells of the body. 
 The ophthalmic artery supplies the eye with blood. 
 
 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 position. As a 
 rule, an artificial eye will last about a year, when 
 it begins to lose its smoothness and a new one 
 is required. 
 
 Asep'sis. Free from septic matter, or free from in- 
 fection. 
 
 Asthenopia (as-then-o'-pi-ah). Weak and painful 
 vision; subdivided into three kinds: retinal, 
 muscular, and accommodative. 
 
 Retinal — where the eye cannot stand light with- 
 out pain; intolerance of light; photophobia. ^ 
 
LEWIS POCKET 
 
OPTICAL DICTIONARY. 25 
 
 Muscular — a condition of the eyes in which the 
 muscles controlling their movement sufiFer from 
 speedy fatigue, causing pain. 
 
 Accommodative — fatigue of the ciliary muscles 
 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") . Astigmatism is a 
 term applied to an eye whose refraction is not 
 the same in all its parts, and it is subdivided into 
 two kinds, regular and irregular. Irregular 
 astigmatism is where there is a difference of refrac- 
 tion in one and the same meridian, and according 
 to Hartridge is sur divided into normal and ab- 
 normal. Normal irregular astigmatism is due in 
 a great measure to irregularities 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 cornea, or injury of the cornea, 
 but the same condition may be congenital. This 
 kind of astigmatism cannot be corrected with 
 lenses. Regular 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 
 focuses, which are as follows: 
 
 No. 1. Compound Hyperopic Astigmatism is 
 that condition in which the foci of the two princi- 
 pal meridians are back of the retina at different 
 
26 
 
 LEWIS POCKET 
 
 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 
 
 No. 2. Simple Hyperopic Astigmatism. 
 
 on the retina, the other behind the retina, when 
 the eye is at rest. 
 
 No, 3, Compound Myopic Astigmatism. 
 
 No. 3. Compound Myopic Astigmatism is 
 that condition in which the two principal merid- 
 
OPTICAL DICTIONARY. 
 
 27 
 
 ians focus in front of the retina at different 
 places when the eye is at rest and looking at 
 infinity. 
 
 No. 4. Simple Myopic Astigmatism, 
 
 No. 4. Simple Myopic Astigmatism is that 
 condition in which one of the principal meridians 
 focuses on the retina and the other in front with 
 the eye at rest and looking at infinity. 
 
 No. 5. Mixed Astigmatism. 
 
 No. 5. Mixed Astigmatism is that condition 
 in which one of the principal ^meridians focuses 
 in front of the retina and the other behind the 
 retina when the eye is at rest and looking at 
 infinity. It derives its name, mixed astigmatism, 
 from the fact that one meridian is hyperopic and 
 the other myopic. 
 
 Corneal Astigmatism is caused by irregu- 
 larity of the curvature of the cornea. 
 
\ 
 
 LEWIS POCKET 
 
 Lenticular Astigmatism is caused by an irreg- 
 ularity of the curvature of the crystalline lenis. 
 
 Astigmatism with the Rule is where the axis 
 of a minus cylinder that will correct the astigma- 
 tism is nearer the 180th meridian than the 90th, 
 or the axis of a plus cylinder that will correct the 
 astigmatism is nearel- 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 meridians, 
 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 hie 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 improvement, if any. It is not uncommon 
 for cases, of say 4-D., of astigmatism to see very 
 little better with their glasses at the tinie of fitting, 
 but if they are worn persistently the vision is 
 expected to improve in a few months. 
 
 ^.stringent (as-trin'-jent). An agent that causes 
 contraction and arrests discharges. 
 
 A.syininetry (ah-sim'-et-re). When the eyes do not 
 correspond, or resemble each other in appeal ance, 
 they are said to lack symmetry. 
 
OPTICAL DICTIONARY. 29 
 
 Atrophy. A wasting away of a part from a lack 
 of nutrition. 
 
 Atropine. A mydriatic which is used more than 
 any other to suspend accommodation and dilate 
 the pupil. Atropine paralyzes the sphincter 
 muscle of the iris and the ciliary muscle, and 
 hence results in dilatation of the pupil, and also 
 in inability to see clearly near by. The dilata- 
 tion of the pupil is a maximum one. If, in the 
 case of a dilatation of the pupil caused by oculo- 
 motor paralysis, atropine is instilled, the pupil 
 becomes still more dilated. This proves that 
 atropine, besides producing paralysis of the con- 
 tracting 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 maxi- 
 mum. Commencing with the third day it begins 
 to decrease again, but does not disappear com- 
 pletely 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 employed 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 atropine. 
 
 Autophthalmoscope (au-tof-thal'-mo-skope). An 
 ophthalmoscope planned in such a way that a 
 person can examine his own eyes. 
 
 Axial. Of, or pertaining to, an axis. 
 
 Axially. In the direction of the axis. 
 
30 LEWIS POCKET 
 
 A.xis. Straight line through a center, on which the 
 body is supposed to revolve. The^eye has two 
 principal axes, the optic and visual. vThe optic 
 axis is an imaginary line through the center of the 
 cornea, through theoiodal points to the inner side 
 of the macula lutea.\The visual axis is a line 
 from the center of the macula lutea, through 
 the nodal point to the object looked at. When 
 speaking of the axis of a cylinder we mean the 
 meridian ' of a cylindrical lens having no power. 
 When parallel rays fall on the spherical surface of 
 a lens, the ray which strikes the optical center 
 at right angles will pass through unrefracted, 
 and is known as the principal axis. 
 
 Axis of Refraction. The normal to the surface of a 
 refracting medium at the point of incidence of 
 a ray of light. 
 
 Axonometer (ax-o-nom'-e-ter) . Apparatus for rap- 
 idly determining the axis of a cylindrical lens. 
 
 xSacillar Layer (bas'-il-ar) . The layer of rods 
 and cones of the retina. 
 
 Barometer. An instrument indicating the atmos- 
 pheric pressure. 
 
 Basalts Lamina. Or membrane of Bruch. The 
 membrane which separates the choroid from the 
 pigmentary layer of the retina. 
 
 Base. Foundation or thick end of a prism. 
 
 Beer's Knife. A knife with a triangular blade for 
 corneal incision. 
 
OPTICAL DICTIONARY. 31 
 
 Bi, Is employed to signify two things in one; for 
 instance, bifocal, biconcave, biconvex. 
 
 Biconcave. Concave on both sides. 
 
 Biconvex. Convex on both sides. 
 
 Bifocal. Double focus. There are six kinds, 
 namely : 
 
 No. 1. Solid bifocal. 
 
 No. 2. Split or Franklin bifocal. 
 
 No. 3. Perfection bifocal. 
 
 No. 4. Cemented bifocal. 
 
 No. 5. Invisible bifocal. 
 
 No. 6. Depressed bifocal. 
 
 The solid bifocal is now out of date. The split 
 or Franklin bifocal must be worn in rims, while 
 the depressed, invisible, and cemented can be 
 mounted without rims, but cannot be worn near 
 intense heat. A bifocal lens consists of two parts 
 of two different foci. In 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 accommodation. 
 
 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 onto 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 
 
32 LEWIS POCKET 
 
 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. Pertaining 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. 
 
 Biorbital Angle. The same as the optic angle. 
 
 Birefractive. Doubly refractive. 
 
 Blear-eye. Marginal blepharitis. 
 
 Blennorrhea (blen-or-e'-ah) . Excessive mucous 
 discharge. 
 
 Blepharadenitis (blef-ar-ad-en-i'-tis) . Inflammation 
 of the meibomian glands. 
 
 Blepharal (blef ^-ar-al) . 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 the patient to refrain from 
 winking. (Blinking.) 
 
 Blepharitis (blef-ar-i'-tis) . Inflammation of the 
 eyelids. Ciliaris b. That condition where the 
 hair follicles of the eyelids are inflamed. 
 
OPTICAL DICTIONARY. 33 
 
 Blepharoplegia (blef-ar-o-ple'-ge-ia). That state in 
 which the eyelid is paralyzed, causing ptosis. 
 
 Blepharoptosis (blef-ar-op-to'-sis). That condition 
 where the upper eyelid droops from paralysis. 
 
 Blepharospasm (blef -ar-o-spasm) . That condition 
 in which there is a spasm of the orbicular muscle 
 of the eyelids. 
 
 Blepharostat (blef-ar'-o-stat) . An instrument used 
 for holding the eyelids apart. 
 
 Blepharostenosis (blef-ar-o-ste-no'-sis) . A narrow- 
 ing of the palpebral slit between the eyelids. 
 
 Blepharosynechia (blef-ar-o-sin-ek'-i-a) . A condi- 
 tion in which there is a growing together of the 
 eyelids. 
 
 Blepharotomy (blef-ar-ot'-o-me). 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 
 ' papilla. It is the entrance of the optic nerve 
 on the retina. 
 
 Blinking. That condition in which there is slt 
 involuntary winking. 
 
 Bonnet's Capsule. The same as Tenon's Capsule. 
 
 Bowman's Membrane. The second anterior layer 
 of the cornea. 
 
34 LEWIS POCKET 
 
 Brachymetropia (brach-e-me-tro'-pe-a) . The same 
 as myopia and hypometropia. It is an eye where 
 parallel rays of light will fociis in front of the 
 retina with the muscles of accommodation at rest. 
 
 Brain. A nervous mass within the skull. 
 
 Buphthalmia (buf-thal'-meh-ah) . Enlargement of 
 the eye. 
 
 Bupiithalmus. (See Buphthalmia.) 
 
 \ 
 
 V 
 
 l^yampimeter (kam-pim'-e-ter) . An instrument 
 for measuring the field of vision. 
 
 Canada Balsam. A product obtained from a tree 
 that grows in Canada, and is used for the purpose 
 of cementing lenses. It is easily melted if heated, 
 and readily soluble in alcohol. 
 
 Canals of Fontana. A number of little spaces or 
 openings between the iris and cornea, in the 
 sclerotic. (See Anatomy.) 
 
 Canal of Petit. The space which surrounrls the 
 crystalline lens between the suspensory ligaments. 
 
 Canal of Schlemm. Circular canal surrounding the 
 eye at sclerocorneal junction. (See Anatomy.) 
 
 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 
 iens, during development of the eye. The artery 
 then disappears, but the canal remains. 
 
OPTICAL DICTIONARY. 35 
 
 Canthectomy (kan-thek'-to-my). An operation in 
 which part of the can thus is cut away. 
 
 Canthitis (kan-thi'-tis) . Inflammation of the angles 
 of the eyelids. 
 
 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. The angle at the junction of the eyelids, 
 known as the inner and outer canthi. 
 
 \ 
 
 Capsule (kap'-sule). A sac which encloses an organ 
 for the purpose of support, protection, and lubri- 
 cation. 
 
 Capsule of Tenon. (See Tenon's Capsule.) 
 
 Capsulitis (knp-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. (See Nodal Point.) * 
 
 Cartilage (kar-'til-aj). The gristle or white elastic 
 substance in different parts of the body. 
 
 Caruncula Lachrymalis (kar-un'-ku-lah) . Is the 
 small reddish body at the inner canthus of the eye. 
 
 Cast. A cast in the eye would apply to strabismus, 
 or squint. 
 
\ 
 
 36 LEWIS POCKET 
 
 Cataphoria (kat-af-o'-re-ah) . A tending of one eye 
 downward. If it is the right eye it is right 
 cataphoria, and if it is the left eye it is left cat- 
 aphoria. Esocatophoria is the tendency of the 
 visual line inward and downward. Exocato- 
 phoria is the tendency of the visual line outward 
 and downward. 
 
 Cataract (kat'-ar-akt) . Any opacity of the crys- 
 talline lens or lens capsule of the eye. i^ Lenticu- 
 lar c, an opacity of the lens proper.V Capsular c, 
 
 ' an opacity of the lens capsuJe.V Senile c.,* an 
 opacity of the lens due to age. v Traumatic c, a 
 cataract 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 hya- 
 loid membrane becoming opaque. 'Cortical c, 
 that condition in which the border or outer layeis 
 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 an- 
 terior or posterior pole of the lens. 
 
 Catop'trics. Laws of reflection of light. 
 
 Catoptric Test (kat-op'-trik). A test for cata- 
 ract by light reflected from the crystalline lens. 
 In. this test ask the patient to look straight ahead, 
 then hold a lighted candle 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 cap- 
 sule you will notice three images of the candle. 
 The first will be on the surface of the cornea in an 
 upright position, the second will be on the an- 
 
OPTICAL DICTIONARY. 37 ' 
 
 terior surface of the lens, also upright, while the 
 tliird 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. 
 
 Cat's-eye Pupil. Where the pupil of the eye is long 
 and narrow (slit-like). 
 
 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. (For Optical Center see 
 appendix). , 
 
 Centimeter (sen'-tim-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 
 radian. 
 
 Centric (sen'-trik). Pertaining to a nerve center. 
 
 Ceratitis (ser-at-i'-tis). The same as kenititis. 
 
 Ceratonosus (ser-at-on'-o-sus). Any disease of the 
 cornea. 
 
 Ceratotome (se-rat'-o-tom). A knife for dividing 
 the cornea. 
 
 V Chalazion (chal-a'-zi-on). 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 depressions are small tubular glands, called 
 meibomian glands, and their ducts open next to 
 
38 LEWIS POCKET 
 
 the margin of the lid. A chalazion is an enlarge- 
 ment of one or more of these glands, due to the 
 stoppage 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 abscess. 
 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 sebaceous 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 position 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 factors in producing chalazion. 
 
 Chambers. The spaces of the eye. Anterior c, the 
 space between the cornea and the iris. Posterior 
 c, the space between the iris and the lens. 
 
 \/ 
 
 Check Ligament. A few fibers 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 probably 
 prevent or retard over-action of the abductor^ 
 or adductors. 
 
OPTICAL DICTIONARY. 39 
 
 Cheniosis (ke-mo'-sis) . Edema of the conjunctiva 
 of the eye. 
 
 Chiasm (ki'-asm). A crossing; especially the cross- 
 ing of the fibers of the optic nerve (optic com- 
 missure) . 
 
 Chiastometer (ki-as-tom'-e-ter) . An instrument for 
 ascertaining the deviation of the optic axis. 
 
 Chlorophaue (klo'-ro-fan). A green-yellow pigment 
 irom the retina. 
 
 ^ Choked Disc. Congested and inflamed state of the 
 optic disc. 
 
 Chondral (kon'-dral). Pertaining to cartilage. 
 
 Choroid (ko'-roid). A part of the second tunic. 
 (See Tunic.) 
 
 Choroidal Fissure. The opening in the choroid 
 through which the optic nerve passes to form the 
 retina. 
 
 Choroideremla (ko-roi-de-re'-me-ah). Absence of 
 the choroid. 
 
 Choroiditis (ko-roi-di'-tis). Inflammation of the 
 choroid. 
 
 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, 
 
40 LEWIS POCKET 
 
 Chromatic (kro-mat'-ik). Relating to color. 
 
 Chromatic Aberration. (See Aberration.) 
 
 Chromatodysopia (kro-mat-o-dys-o'-pi-ah) . Color- 
 blindness. 
 
 Chromatology (kro-mat-ol'-o-gy) . The study of 
 colors. 
 
 Chromatom'eter. An instrument for measuring 
 color or color perception. 
 
 Chromatophobea (kro-mat-o-fo'-be-ah). An ab- 
 normal fear of color. 
 
 Chromatopsia (kro-mat-op'-se-ah) . Abnormal sen- 
 sation of color, due to disorders of the optic cen- 
 ters, or to drugs, especially santonin. 
 
 Chromatoptometry (kro-mat-op-tom'-et-ry) . Tak- 
 ing the measurement of the power of color per- 
 ception. 
 
 Chromometer (kro-mom'-et-er) . An instrument for 
 measuring coloring matter present. 
 
 Chronioptometer (kro-mop-tom'-et-er). An instru- 
 ment to test the color sense. 
 
 Cibisitome (sib-is'-it-om) . An instrument for in- 
 cising the lens capsule. 
 
 Cilia. The eyelashes. Hair. 
 
 Ciliariscope (sil-i-arMs-cope). An ins^v^xument for 
 examining the ciliary region of the eye. 
 
 Ciliary (sil'-i-a-ry) Pertaining to, or like, the eye- 
 lashes. 
 
OPTICAL DICTIONARY. 41 
 
 Ciliary Body. The middle part of the second tunic, 
 composed of ciliary processes, ciliary veins, ciliary 
 muscles, ciliary nerves and arteries. 
 
 Cillo (cilMo) or Cillosis. A trembling or spasmodic 
 twitch of the eyelids. 
 
 Cinerea (sin-e'-re-ah). The gray matter of the 
 nervous system. 
 
 Cut showing Chori^id Ciliary Muscle and Nerves. 
 
 Circles of Haller. Venous and arterial circles of the 
 eye. 
 
 Circulation (cir-cu-la'-shun). The passage of blood 
 in going from and returning to the heart after 
 having made a circuit of the body. 
 
 \ Clonic Spasm. An intermittent involuntary con- 
 ^ traction of the ciliary muscles, which shows itself 
 when the eye is in use. 
 
*2 LEWIS POCKET 
 
 Cocain (ko-ka'-in). A local anesthetic and mydri- 
 atic. Cocain dilates the pupil, and hence would 
 seem to call for mention in this place, although, 
 strictly speaking, it does not belong to the myd- 
 riatics proper — that is, the dilatation of the pupil 
 by cocain 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 cocain 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 cocain is the most complete 
 that can possibly be attained. The accommo- 
 dation is not paralyzed by cocain, but only 
 somewhat weakened. 
 
 CoUyrium (col-lyr'-i-um). Any lotion to be dropped 
 in the eye. 
 
 V Coloboina (kol-o-bo'-mah). A tear or break in the 
 eyeball, as in the iris or choroid. 
 
 Golor-Blindness (Achromatopsia). Bhndness for one 
 or more colors. Due to the absence from the 
 retina of one or two of the three primary sub- 
 stances (according to Hering). The test is made 
 by presenting the patient with samples of differ- 
 ent colored yarns — a number of each color, but 
 different shades — and the patient is requeste/i to 
 separate them. Persons having this anomaly of 
 vision are generally unaware of it themselves. 
 
OPTICAL DICTIONARY. 4^ 
 
 Uommissure (kom'-mis-ur) (Optic). The crossing 
 of the two optic nerves. 
 
 Compound. A lens that contains a sphere and a 
 cylinder. 
 
 Comus (ko'-mus). A cone. A crescentic patch 
 of atrophic choroid tissue near the optic papilla 
 in myopia. 
 
 Concave. The negative of 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. Having a common center. 
 
 Concomitant (kon-com'-it-ant) . Accompanying. 
 Concomitant Squint is a condition where the two 
 eyes deviate, but accompany one another in their 
 movement. The object can be seen by either 
 eye, but not the two eyes at the same time. 
 
 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 ametropia, which must be 
 properly centered as to pupillary distance, and a 
 solid blank disk is put into the cell in front of the 
 other eye. The patient's attention is then di- 
 rected 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 ap- 
 pear i^ the center of the circle. If there is mus- 
 
14 LEWIS POCKET 
 
 cular srror the light will be either above or below 
 or to one side of center, and can be brought to 
 .•:enter by the proper prism with base in proper 
 position. This does away with necessity for com- 
 
 Cone. 
 
 putations where there is combined prismatic error 
 in different angles, and gives at once the position 
 of the base of the correcting prism. (See Muscu- 
 lar Imbalance.) 
 
 Conical Cornea. A condition of the cornea in which 
 it bulges forward in the shape of a cone. 
 
 Conjugate (coupled). 
 
 Conjugate Foci (kon'-ju-gat). Two points so sit- 
 uated 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. 
 
OPTICAL DICTIONARY, id 
 
 Conjunctiva (kon-junc-ti'-va). The mucous mem- 
 brane lining the eyeUds and anterior covering c>f 
 the cornea, and is supplied by a branch of the 
 fifth sensory nerve (ophthalmic). 
 
 V 
 
 Conjunctivitis (kon-junc-tiv-i'-tis). Inflammation of 
 the conjunctiva. 
 
 Convergence (kon-ver'-gence). The power of turn- 
 ing the two eyes to a given point inside of infinity. 
 In the emmetropic eyes of a healthy person, the 
 two functions of accommodation and conver- 
 gence work together so that they can scarcely be 
 performed separatel3\ Yet their objects are 
 totally different, but their harmonious co-opera- 
 tion is none the less essential. The function of 
 accommodation has for its purpose the formation 
 of a clearly defined image on the retina of each 
 eye singly; while the function of convergence is 
 the fusing of the two retinal images into a single 
 sensory perception; that is to say, the turning of 
 the two eyes inward so that the image will fall 
 on corresponding parts of each retina; but an 
 object at a given distance will always require 
 from the same pair of eyes the same amount of 
 accommodation, and it will also require from 
 them the same amount of convergence. Say the 
 object is at thirteen inches, where it will require 
 three diopters of accommodation, then it will also 
 require three meter angles of convergence; that 
 is to say, convergence to such a degree that the 
 lines of direction of the two eyes would intersect 
 at a point thirteen inches from them; and further, 
 that if the object was brought nearer, the accom- 
 modation and convergence would increase to an 
 equal extent. When one's eyes accommodate 
 
46 LEWIS POCKET 
 
 more than they converge, in order to see at a 
 single point, they are hyperopic to the extent 
 of the difference between the two functions; 
 and when they converge more than they accom- 
 modate for a given point, they are myopic the 
 difference. This of course refers to errors of 
 refraction. 
 
 Convergent, Turning 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) . A worn-out state of the 
 eye, caused by eye strain. 
 
 Coreclisis (kor-ek'-lis-is). 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. 
 
 Corectopia (kor-ec-to'-pi-ah). 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 (kor-el'-ys-is) . Detachment of adhesions 
 of the iris to the cornea or the lens capsule. 
 
OPTICAL DICTIONARY. 47 
 
 Coremorphosis (kor-e-mor'-pho-sis) . Creation of an 
 
 artificial pupil. 
 Coreometer (kor-e-om'-et-er) . A contrivance used 
 
 for measuring the pupil. 
 
 Cornea (kor'-ne-ah) . The anterior and transparent 
 V part of the eyeball. It has no blood-vessels, but 
 plenty of nerves and lymphatics. It serves to 
 transmit light into the eye. It is convex in front 
 and concave behind. Its curvature varies in 
 different individuals. It is composed of five 
 layers, arranged as follows, from without inward: 
 namely, (1) Conjunctiva epithelium; (2) Bow- 
 man's Membrane; (3) Cornea proper; (4) Mem- 
 brane Descemet; (5) Endothelium. The third 
 layer (cornea proper) is the foundation layer of 
 the cornea. It is composed of a horn-like sub- 
 stance and is non-sensitive and merely serves to 
 keep the cornea in shape. Th(^ second layer 
 (Bowman's Membrane) 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 first layer 
 (Conjunctiva epithelium) serves to protect the 
 nerves in Bowman's Membrane from cold, wind, 
 and dust, and at the same time gives a highly 
 polished surface to the cornea. The fourth layer 
 (Membrane Descemet) is a layer similar to Bow- 
 man's Membrane, and protects the cornea proper 
 from any diseased condition from the posterior 
 side. The fifth layer (Endothelium) is a lining 
 membrane 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. 
 
48 LEWIS POCKET 
 
 Cor'neal. Pertaining to the cornea. 
 
 Corneal Astigmatism. (See Astigmatism.) 
 
 Corneal Facets (fas'ets). Small, plain distinct sur- 
 faces of the cornea. 
 
 Corneitis (cor-ne-i'-tis)., Inflammation of the cornea. 
 
 Corneo-iritis. Inflammation of the iris and cornea. 
 
 Correction. Making good an abnormal condition, 
 such as correcting an error of refraction. 
 
 Cortical (kor'-tik-al) . To be near the border. 
 Cortical cataract is that variety in which the 
 opacity begins at the border of the crystalline 
 lens and gradually spreads toward the center, 
 which it sooner or later involves. 
 
 Couching. That condition in which the lens is dis- 
 placed in cataract. This operation is now obso- 
 lete. 
 
 Cover Test. A test for muscular imbalance by 
 covering one eye and observing its movement 
 while uncovering; the point of fixation being 
 established. 
 
 Cramp. A spasmodic muscular contraction. 
 
 Cribriform (krib'-rif-orm). Perforated like a sieve. 
 
 Critical Angle (krit'-ik-al) . The least angle of 
 incidence at which a ray of light traveling in a 
 denser medium is totally reflected at the surface 
 which separates it from a rarer medium; also 
 known as limit angle. 
 
 Crossed Diplopia. (See Diplopia.) 
 
OPTICAL DICTIONARY. 
 
 411 
 
 Crystalline Lens (krys'-tal-een) . The lens of the 
 eye which resembles a crystal, located behind the 
 iris, and is made up of layers like an onion, which 
 give it an elastic nature. The lens itself is en- 
 closed in the lens capsule, which is held in its posi- 
 tion by the suspensory ligaments. Its index of 
 refraction is 1.43. The lens of the eye repre- 
 sents from 19 to 20D. of plus when at rest. 
 
 Crytometer. (See Curtometer.) 
 
 Cupped Disc, 
 
 \ Cupped Disc. That condition in which the optic 
 disc has become cupped, as seen in glaucoma. 
 
 Curtom'eter. An instrument for measuring curved 
 surfaces. 
 
 Curvature (curv'-r.-ture) . The bending of a line 
 withoat forming angles. 
 
50 LEWIS POCKET 
 
 Cyclitis (cyc-li'-tis). Inflammation of the ciliary 
 body. 
 
 Cyclochoroidi'tis. Inflammation of the choroid and 
 ciHary body. 
 
 Cyclophoria (cyc-lo-fo'-ri-ah). That condition in 
 which the vertical axis of the eye inclines to the 
 right or left instead of standing vertically, the ex- 
 trinsic muscles being at rest. 
 
 Cyclopia (si-klo'-pe-ah) . A single eye in center 
 of forehead. 
 
 Cycloplegia (cy-clo-ple'-gi-ah). Paralysis of the 
 ciliary muscles. 
 
 Cycloplegic. A drug which produces para/ysis of 
 the ciliary muscles, or muscles of accommodation. 
 
 Cylinder (cylMn-der). (See Lens.) 
 
 Cystitome (sis'-tit-om). An instrument used for 
 opening the sac of the crystalline lens. 
 
 JLl» Abbreviation for diopter, dexter, or dose. 
 
 Dacryadenalgia (dak-ry-ad-en-ar-gi-ah) . Pain in a 
 lacrimal gland. 
 
 Dacryagogue (dak'-ry-ag-og). A medicine which 
 causes a flow of tears. 
 
 Dacryoadenitis (dak-ry-o-ad-en-i'-tis) . Inflamma- 
 tion of a lacrimal gland. 
 
 Dacryocele (dak'-ry-o-cele) . A cyst of the lacrimal 
 sac. 
 
OPTICAL DICTIONARY. 61 
 
 k)acryocyst (dak'-ry-o-cyst) . The tear sac. 
 
 Dacryocystalgia (dak-ry-o-cyst-al'-gi-ah). Pain in 
 the lacrimal sac. 
 
 . Dacryocystitis (dak-ry-o-cys-ti'-tis). Inflammation 
 V of the lacrimal sac. 
 
 Dacryoma (dak-ry-o'-ma). A lacrimal tumor 
 which causes an obstruction of the lacrimal 
 puncta, so that the tears flow over the lids 
 upon the cheek. 
 
 Dacryon (dak'-re-on). The lacrimal point; a place 
 where the lacrimal, frontal, and upper maxillary 
 bones meet. 
 
 Dacryops (dak'-re-ops) . That condition in which 
 there is distention of a lacrimal duct. 
 
 Dacryorrhea. Excessive or morbid flow of tears. 
 
 Daltonism (dawr-ton-izm). Color-blindness. 
 
 Day-blindness (day-blind'-ness) . Partially blind by 
 day, with better vision at night. 
 
 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 
 center. 
 
 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 
 
52 LEWIS POCKET 
 
 lens. The optical center of a plus lens is at its 
 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-diopter 
 lens decentered 9.4 millimetres will give the 
 effect of a 1-degree prism, while a 2-D. lens will 
 only require to be decentered half this amount, 
 or 4.7 millimetres; a 3-D. lens, one-third of this 
 amount, or 3. 1 + mm. for the same effect, and 
 so on according to the strength of the lens. To 
 obtain the effect of a 2-degree prism these lenses 
 ' must be decentered twice as much, that is to saj^, 
 a 1-D. lens, 18.8 mm.; a 2-D. lens, 9.4 mm.; a 
 3-D., 6.3 mm. From this table one can easily 
 figure the exact amount any lens should be de- 
 centered to obtain a given prismatic effect. 
 
 Decentration (de-cen-tra'-tion). The act of remov- 
 ing from a center. 
 
 Decimeter (des'-im-e-ter) . One-tenth of a meter- 
 Defect (de-fectO. 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. 
 
 Depilation (dep-il-a'-shun). The removal or loss 
 of the hair. 
 
 Deplumation (de-plu-ma'-shun) . Loss of eyelashes 
 by disease. 
 
 Deprimens Oculi (dep'-ri-mens ok'-u-li). The rectus 
 inferior muscle. 
 
OPTICAL DICTIONARY. 53 
 
 Descemet^s Membrane (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) . Turning aside, as in stra- 
 bismus. Conjugate d., deviation of both eyes to 
 the same side. Minimum d., the smallest devia- 
 tion of a ray that a given prism can produce. 
 
 Dexter, Dextra (dex'-ter, dex'-tra). On right side. 
 
 Dextrad (dex'-trad). Toward the right side. 
 
 Diameter (di-am'-e-ter) . A straight line joining 
 opposite points of a circle. 
 
 Diaphaneity (di-af-a-ne'-i-ty) . Transparency; the 
 power of transmitting light. 
 
 Diaphanous (di-af '-a-nous) . Having power to 
 transmit rays of light, as glass. 
 
 Diaphragm (di'-af-ram) . A term applied to the 
 partition with a central aperture in optical in- 
 struments so that rays of light may be controlled. 
 The iris with its pupil constitutes the diaphragm 
 of the eye. 
 
 Diapyesis (di-ap-i-e'-sis). Suppuration. 
 
 Diffraction (dif-f rak'-shun) . Deflection or decom- 
 position of light in passing by the edges of opaque 
 bodies or through small apertures. 
 
 Diffusion (dif-f u'-shun) . A spreading or scattering 
 of rays of light, causing a blurred image by im- 
 perfect refraction. 
 
 Dilatant. A medicine that causes dilatation. 
 
54 LEWIS POCKET 
 
 Dilatation (di-la-ta'-shun). The expansion of any 
 orifice or canal. 
 
 Dilator (di-la'-tor). Dilator iris refers to th« radi- 
 ating fiber of the iris which dilates the pupil. 
 
 Diopter (di-op'-ter) . A lens of one meter focus is 
 taken as the unit frorh the metric system, and is 
 called a diopter. A lens of two diopters is twice 
 the strength of the former, and has a focal length 
 of half a meter. Synonyms, Dioptre and 
 Dioptry. 
 
 Dloptometer (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 (di-op'-tral). Pertaining to a diopter. 
 
 Dioptrics (di-op'-triks). Pertaining to refracted 
 light. 
 
 Dioptry (di-op'-tre). (See Diopter.) 
 
 Diplocorla (dip-lo-ko'-re-ah) . Double pupil. 
 
 \ Diplopia (dip-lo'-pe-ah). Double vision. The ob- 
 ject 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 ^ich do not 
 exactly correspond in the two eyes. V Heterony- 
 mous d., where the object seen with the right 
 eye appears 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. 
 
V 
 
 OPTICAL DICTIONARY. 65 
 
 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) . 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) . Points on the 
 two retinae upon which light does not produce the 
 same impression. 
 
 Dispersing Lens (dis-per'-sing). Same as • con- 
 cave lens. 
 
 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) . 
 That condition of the eyelashes in which a second 
 row rubs against the cornea, causing inflammation. 
 
 Divergence (di-ver'-gens) . To turn outward froOl 
 parallelism. 
 
56 LEWIS POCKET 
 
 Donders (Frans Cornelia). A Dutch physician, born 
 t Tilburg, Holland, May 27, 1818. He was 
 educated at Utrecht, where he became a profes- 
 sor of physiology, histology, and ophthalmology 
 in 1847. Among his works are, **A Study of 
 the Movements of the Eyes," "Astigmatism,'' 
 "Anomalies of Refraction and Accommodation.'* 
 He died March 27, 1889. 
 
 Double Prism. 
 
 Double Prism. An opaque disc with a slit-like 
 opening. Over this slit there are two prisms 
 with their bases together. Used for testing for 
 muscular imbalance. 
 
 Double Vision. Seeing two images instead of one. 
 (See Diplopia.) 
 
 Doublet (doubMet). Composed of two lenses. 
 V pynamic Refraction (dy-nam'-ic). The refraction 
 of the eye when adjusted for the near point. The 
 differenf'e between the dynamic and static refrac- 
 tion is known as the Amplitude of Accommodation 
 
\. 
 
 OPTICAL DICTIONARY. 57 
 
 -Kccentric (ek-sen'-trik) Away from a center. 
 
 Ecchyraosis. An extravasation of blood into tissue. 
 
 Ectasia (ek-ta'-se-ah) . Abnormal distention or 
 dilatation of a part. 
 
 E^tiris (ek-ti'-ris) . The external portion of the iris. 
 
 Ectochoroidea (ek-to-cho-roi'-de-ah). The outer 
 layer of the choroid coat. 
 
 Ectocornea (ek-to-kor'-ne-ah) . Outer layer of the 
 cornea. 
 
 Ectoretina (ek-to-ret'-in-ah) . Outermost layer of 
 the retina. 
 
 Ectropion (ek-tro'-pi-on) Ectropium. Turning out 
 or inside out of the edge of an eyelid. 
 
 Em'bolism. Obstruction of a vessel by an embolus. 
 
 Em'bolus. A clot or plug which obstructs a blood- 
 vessel. 
 
 Emergent. A ray of light after having passed 
 through a refracting medium. 
 
 Emissive. Radiating. 
 
 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 aw^y 
 that the rays appear to be parallel because the divergence 
 is so slight. 
 
58 LEWIS POCKET 
 
 Emmetropia (em-met-ro'-pi-ah) . An eye where 
 parallel rays of light will focus on the retina with 
 the muscles of accommodation at rest. (Cut, 
 p. 57.) 
 
 Encan^this. A minute tumor in the inner canthus 
 of the eye. 
 
 Enophthalmus (en-of-thal'-mus). A condition 
 where the eyes are deep-seated. 
 
 Enstrophe (en'-stro-fe). A turning inward. 
 
 En'tad. Toward a center. 
 
 Entochoroidea (en-to-cho-roi'-de-ah) . The inner 
 layer of the choroid. 
 
 Entocornea (en-to-cor'-ne-ah). Descemet's Mem- 
 brane. 
 
 Entoptic (en-top'-tic) . Situated within the eye. 
 
 Entoptoscppy (en-top-tos'-co-py) . Inspection qf the 
 interior of the eye. 
 
 Entoretina (en-to-ret'-in-ah) . The nervous or inner 
 layer of the retina. 
 
 Entropion. (See Entropium.) 
 
 \' Entropium (en-tro'-pi-um) . A turning in or inver- 
 sion of the eyelid or eyelashes. 
 
 Enucleate (e-nu'-cle-ate) . To remove from its cover. 
 
 Enucleation (e-nu'-cle-a'-shun) . jOperation for the 
 removal of the eye. 
 
 Epicanthus (ep-i-can'-thus) . A fold of skin pro- 
 jected over the inner canthus. 
 
OPTICAL DICTIONARY. 59 
 
 Epipbora (e-pif '-or-a) . An overflow of tears, caus- 
 ing them to run down the cheek. 
 
 Episcleral Cep-i-scie'-ral)- Situated over the sclera 
 ot the eye. 
 
 Episcleritis (ep-i-scle-ri'-tis) . Inflammation of the 
 outer layers of the sclera. 
 
 Equiribrating operation. Tenotomy of the muscle, 
 which antagonizes a paralyzed muscle of the eye. 
 
 Errors of Refraction. Abnormal conditions of 
 refraction in the eye. 
 
 Erythropsia (er-ith-rop'-se-ah) . Red vision. 
 
 \ Eserine (es'-er-een) . An alkaloid obtained from the 
 \r 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 adjustment 
 of the eye for the near point, as if marked myopia 
 were present. We generally apply sulphate of 
 eserine in one per cent solution. This solution, 
 when freshly prepared, is colorless, 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 one 
 to two per cent solution, is recommended as a 
 miotic for ordinary use. Its solution keeps 
 
60 LEWIS POCKET 
 
 better than that of eserine, and does not act as 
 powerfully as the latter, but is not accompanied 
 by any unpleasant complications. Eserine is 
 best reserved for those cases in which pilocarpine 
 is ineffectual. 
 
 \^ Esophoria (es-o-f o'-ri-ah) . A tendency of the eyes 
 to deviate inward, usually caused by hyperopia. 
 
 Esotropia (e-so-tro'-pi-ah) . 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. 
 
 V 
 
 Excavation (ex-cav-a'-shun). Excavation of optic 
 nerve; cupping or hollowing of the optic disc. 
 
 Exophoria (ex-o-f o'-ri-ah) . A tendency of the eye 
 to deviate outward. 
 
 Exophthalmic Goiter (eks-off-thal'-mik goi'ter). A 
 goiter with exophthalmos and cardiac palpitation; 
 Basedow's disease; Graves' disease. The most 
 prominent symptoms are protrusion of the eye, 
 excited action of the heart, enlarged thyroid 
 (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); infrequency of involun- 
 tary winking (Stellwag's sign) and abnormal 
 width of the palpebral aperture are also found. 
 
 Exophthalmos (ex-of-thal'-mos). Abnormal prr 
 trusion of the eye. 
 
 Exor'bitism. Protrusion of the eyeball. 
 
OPTICAL DICTIONARY. 
 
 61 
 
 Exotropia (ex-o-tro'-pi-ah) . When the eye is turned 
 outward from parallelism. Divergent strabismus. 
 
 Extraction (ex-trak'-shun). The remrival of a body 
 by surgical means. 
 
 Eye. 
 
 i<3ye. 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 produced on the ground glass of a camera. 
 By means of the optic nerve the image that is 
 received on the retina is conveyed to the brain, 
 
62 LEWIS POCKET 
 
 which recognizes the visual appearances and com- 
 pletes 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. 
 
 Eyelashes. The hair of the eyelids. 
 
 Eyelids. The anterior covering of the eye; that por- 
 tion of movable skin with which the eyeball is 
 covered 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 sup- 
 plied by a separate muscle, levator palpebrae 
 superioris. When the eyelids are open an ellip- 
 tical 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 lachrymaliSo 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 com- 
 mencement of the lachrymal canal. Structures 
 of the Eyelids. The eyelids are composed of 
 
Posterior View of Eyelid showing how 
 the Tears enter the Conjunctiva. 
 
 1. Orbicularis Palpebrarum Muscle. 
 
 2. Opening between the lids (Palpebral 
 
 Fissure). 
 
 3. Lachrymal Glands, where the tears 
 
 have their origin. 
 
 4. Its ducts opening in the fold of the 
 
 Conjunctiva. 
 
 5. Conjunctiva lining inside of lid. 
 
 6. Puncta Lacrimalia, through which the 
 
 tears pass. 
 
 7. Inner Canthus. 
 

 Posterior View of the Palpebral (eyelid) 
 with the Conjunctiva Removed. 
 
 1. Origin of the Tensor-tarsi Muscle. 
 
 2. Superior Oblique Muscle after passing 
 
 through its Trochlea. 
 
 3. Inferior Oblique Muscle. 
 
 4. Attachment of Orbicularis Palpebrarum 
 
 on Nasal side. 
 
 5. Tarsal Cartilages showing position of 
 
 Meibomian Glands. 
 
 6. Opening between the lids known as the 
 
 Palpebral Fissure. 
 
 7. Lower part of Orbicularis Palpebrarum 
 
 Muscle. 
 
 8. The insertion of the Tensor- tarsi Muscle 
 
 near the Puncta. 
 
 9. Lachrymal Sac in the nose. 
 
OPTICAL DICTIONARY. 63 
 
 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 at 
 the margin of the Hds with the conjunctiva. The 
 Subcutaneous Areolar Tissue is very lax and deli- 
 cate, seldom cor* tains any fat, and is extremely 
 liable to serous infiltration. 
 
 Eyepiece. The lens or combination of lenses at the 
 eye end of a telescope or other optical instrument 
 through which the image formed by the object 
 glass is viewed. 
 
 Eyesight. The sense of seeing; sight of the eye; 
 viewing; observation. 
 
 i^ acultative (f ak'-ul-ta-tiv) . The power or ability 
 to maintain extra effort whenever called upon. 
 
 VFalse 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 
 y the distant point at which an object may be seen 
 clearly, with the muscles of accommodation 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. 
 
64 LEWIS POCKET 
 
 Field of Vision, The area or space which the fixed 
 eye can see. 
 
 Filtration Angle. (See Iritic Angle.) 
 
 Fissure (fis'-yur). A narrow cleft or depression. 
 Palpebral Fissure, A slit or opening between the 
 eyelids. 
 
 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, 
 distance between the center of lens and its 
 principal focus. 
 
 Focal Length of Lenses. 
 
 opters. 
 
 • English Inches. 
 
 Centimeters, 
 
 .12 
 
 320 
 
 800 
 
 .25 
 
 160 
 
 400 
 
 .37 
 
 108 
 
 300 
 
 .50 
 
 80 
 
 200 
 
 62 
 
 60 
 
 170 
 
 .75 
 
 52 
 
 130 
 
 .81 
 
 48 
 
 115 
 
 1.00 
 
 40 
 
 100 
 
 1.12 
 
 36 
 
 90 
 
 1.25 
 
 32 ....... 
 
 80 
 
 1.50 
 
 .. 26 
 
 65 
 
 1.75 
 
 22 
 
 55 
 
 2.00 
 
 20 
 
 50 
 
 2.25 
 
 18 
 
 43 
 
 2.50 
 
 16 
 
 40 
 
 2.62 
 
 15 
 
 38 
 
 2.75 
 
 14 .. 
 
 35 
 
OPTICAL DICTIONARY. 66 
 
 Focal Length of Lenses — Continued. 
 
 Diopters. English Inches. Centimeters. 
 
 3.00 13 33 
 
 3.25 12 .. 30 
 
 3.50 11 28 
 
 4.00 10 25 
 
 4:50 9 22 
 
 5.00 8 20 
 
 5.50 7 18 
 
 6.00 6i 16 
 
 6.50 6 15 
 
 7.00 5i 14 
 
 8.00 5 12J 
 
 9.00 4i 11 
 
 10.00 4 10 
 
 11.00 3i 9 
 
 12.00 3i 8 
 
 13.00 3 .. 7i 
 
 14.00 21 7 
 
 15.00 2i .. .- 6J 
 
 16.00 2i 6 
 
 18.00 2J 5i 
 
 20.00. . 2 5 
 
 The above table is approximately correct, yet 
 there is a slight difference in close figuring, but is 
 correct as far as the optometrist is concerned; for 
 instance, a + 1-D. lens has- a focal length of 39 . 37 
 in., while we call it 40. 
 
 Focus (fo'-kus). The point produced by rays of 
 light passing through a convex spherical lens and 
 coming down to a sharp point of light. • 
 
 Folders. A term employed for eye-glasses that can 
 be folded up and placed in a small pocket. 
 
 Follicle (folMk-l). A small secretory cavity or sac. 
 
66 LEWIS POCKET 
 
 Follicular (f ol-ik'-u-lar) . Containing foiiicles. F. 
 Conjunctivitis. A form of conjunctivitis marked 
 by the presence of follicles. This occurs gener- 
 ally in children, and is characterized by the for- 
 mation of small, clear elevations, consisting of 
 adenoid tissue, in the conjunctiva of the lower 
 lid; in some cases they are present also in the 
 retrotarsal fold of the upper lid. 
 
 S. Fontana's Canals or Spaces (f on-tah'-nah) . A ring 
 \ of spaces at the junction of the cornea, iris, and 
 sclera. (See Glaucoma.) 
 
 Foramen (fo-ray'-men) (Optic). Opening for pas- 
 ^ sage of optic nerve and ophthalmic artery at 
 apex of orbit. 
 
 Fornix Conjunctiva. The turn or fold of the con- 
 junctiva. 
 
 Fossae Patellaris (pa-tel-Ia'-ris) (meaning dish-like 
 depression). The depression in the anterior sur- 
 face of the vitreous body in which the crystalline 
 lens lies. Also called the Hyaloid Fossa. 
 
 \. Fovea (f oh'-ve-ah) . A small depression. F. Centra- 
 lis is employed to designate the little depression 
 in the center of the macula lutea. 
 
 Frame Fitting. There are times when patients com- 
 plain that their glasses are not comfortable, yet 
 they have the right correction. The cause of the 
 trouble is sometimes found in the improper adjust- 
 ment of the frames. The fitting of a frame is 
 very important, and if neglected will sometimes 
 destroy the benefit of the most carefully fitted 
 lenses. When a student understands the relation 
 between accommodation and convergence the 
 
Ol^TlCAL DICTIONARY . 6'. 
 
 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 of prisms with their bases out- 
 ward. 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 accommodation 
 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 careful 
 attention it becomes a very easy matter. I will 
 here mention a few points which may be of assist- 
 ance to my fellow-student. 
 
 1st. See that the pupillary distance is correct 
 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 patient 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 slight- 
 ly closer and lower, and the top of the lenses must 
 be inclined forward, so as to be as near as possible 
 at right angles to the line of vision. In this way 
 better vision is enjoyed. 
 
68 LEWIS POCKET 
 
 2d. The lenses should be placed as near the 
 eye as the lashes will permit. 
 
 3d. Never prescribe a small lens for a large 
 face nor a large lens for a small face, but always 
 make the lenses as large as you possibly can with- 
 out interfering with the patient's appearance, 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 time do not press on the flesh. If you de- 
 sire to tilt the lenses do not bend temples, but 
 bend the end piece. All glasses should tilt out- 
 ward 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 commencing 
 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 vari- 
 ous dimensions. Then by finding 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. 
 f Fundus. The fundus of the eye is the solid struc- 
 ture seen by means of the ophthalmoscope, 
 namely, the retina, the blood-vessels, and the 
 optic disc, collectively. 
 Fuscin (fus'-sin). A brown pigment of the retinal 
 epithelium. 
 
\: 
 
 OPTICAL DICTIONARY. 69 
 
 Cranglion Ciliary (gang''-gle-on) . A semi-inde- 
 pendent nervous center in the posterior part of 
 the orbit. 
 
 Qeometrical Center. A point midway between all 
 
 5dges. 
 
 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. 
 
 Qlabel'la, Glaberium. Space between the eye- 
 brows. 
 
 Gland. A secretory organ. Lacrimal g., the gland 
 which secretes the tears. 
 
 Glass. A hard, brittle, artificial substance 
 formed by the fusion of silica, potash, and lead. 
 Under the best conditions it is quite transpar- 
 ent. Nothing definitely is known as to its 
 origin. The Egyptians used it, and glass has 
 been discovered 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). A disease of the eye 
 characterized by increased intraocular tension. 
 In order to fully understand this disease it will 
 be necessary 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. 
 
70 LEWIS POCKET 
 
 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 straining of the ciliary muscles, as in hyper- 
 metropia, thus closing the Spaces of Fontana, the 
 drainage system would be blocked, while the 
 humors continue forming, resulting in a painful 
 intraocular 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, when 
 caused by a disease like iritis. It is a progressive 
 disease, and unless checked by treatment ends 
 in permanent blindness. 
 
 V Symptons 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 accommodation. 
 
 (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, some- 
 what occluding the Spaces of Fontana and inter- 
 fering with the free exit of aqueous humor. As 
 the intraocular tension increases, the stoppage 
 becomes more complete. When the atropine is 
 discontinued the sphincter muscle of the pupil 
 
OPTICAL DICTIONARY. 71 
 
 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 condition 
 may result in glaucoma. For the reasons men- 
 tioned it is, as a rule, unsafe to use atropine 
 after the age of from 30 to 35. 
 
 Glaucomatous (glau-kom'-at-ous). Of the nature 
 of glaucoma. 
 
 Glioma (gly-oh'-mah) . A malignant tumor of the 
 retina. 
 
 Gliosarco'ma. Glioma combined with sarcoma. 
 
 Globulin (glob'-u-lin) . A proteid from the lens. 
 
 Goggles. Spectacles with wire screens for the eyes. 
 
 Goiter (goi'-ter). An enlargement of the thyroid 
 gland. Exophthalmic g. (See Exophthalmic 
 Goiter.) 
 
 Graduated Tenotomy. An incomplete cutting of 
 the tendon of an eye muscle. 
 
 Granular Lids (Trachoma). Roughness and sore- 
 ness of the inside of the eyelids. This roughness 
 is caused by a swelling of the lymph-corpuscles, 
 forming, as it were, little lymphatic glands oi 
 lymphatic follicles. 
 
 Gran'ulc. A small rounded body. G. Layer, one 
 
 of the layers of the retina. . 
 
72 LEWIS POCKET 
 
 xialler's Circles. Arterial and venous circles 
 within the eye. 
 
 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 ircipient glaucoma. 
 
 Hec'tometer. One hundred meters. 
 
 Helcol'ogy. Science of ulcers. 
 
 Helco'sis. The formation of an ulcer. 
 
 Hemeralopia (hem-er-al-o'-pi-ah) . An inability to 
 see at night. 
 
 Hemiachromatopsia (hem-i-a-chro-mat-op'-si-ah) . 
 Color-blindness in one-half, or in corresponding 
 halves, of visual field. 
 
 Hemianopia (hem - i - an - o'- pi - ah) , Hemianopsia. 
 
 Blindness for one-half the field of vision in one or 
 both eyes. 
 
 Hemiopic (hem-e-op'-ik). That condition which 
 affects one eye only. 
 
 Hemophtharmia, Hemophthal'mus. Extravasation 
 of the blood inside of the eye. 
 
 Hemorrhage (hem'-or-aj). 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 modi- 
 fied by anabolism for black, green, or blue, and 
 by catabolism for white, red, and yellow. 
 
V 
 
 OPTICAL DICTIONARY. 73 
 
 Heterochromia (het-er-o-kro'-me-ah) . A difference 
 in color (in the irides or of different parts of the 
 same iris). 
 
 Heteronymous (het-er-on'-im-us) . Crossed. (See 
 Diplopia.) 
 
 Heterophoria (het-er-o-pho'-ri-a) . A tendency cf 
 the visual lines away from parallelism. It is 
 subdivided into eight kinds. When the eyes have 
 a tendency to turn in it is known as esophoria; 
 if a tendency to turn out, it is known as ex- 
 ophoria; if a tendency to turnup, it is known as 
 hyperphoria; if up and in, hyperesophoria, 
 and if up and out, hyperexophoria; if a ten- 
 dency downward, it is known as cataphoria; and 
 if down and in, esocatophoria; if down and out, 
 exocatophoria. Any error of refraction is liable 
 to bring on Heterophoria, and by correcting the 
 error, the Heterophoria will disappear, though 
 it may linger for a month or two. 
 
 Heterophthal'mos. That condition in which the 
 irides differ in color. 
 
 Heterotropia (het-er-o-tro'-pi-a) (Strabismus). This 
 term expresses a stronger meaning than hetero- 
 phoria, where there is merely a tendency, while in 
 heterotropia there is a positive and visible ap- 
 pearance of the eyes turning, and they may turn 
 in any direction, as in heterophoria. When the 
 eye turns up it is hypertropia; if downward, 
 catatropia; if inward, esotropia; if outward, 
 ex otropia. 
 
 Hippus (hip'-us) . Spasmodic pupillary movements^ 
 independent of the action of light. 
 
7* LEWIS POCKET 
 
 Holmgren's Test (holm'-grens) . A color test with 
 a number of different colored yarns representing 
 the various shades of different colors. Used for 
 detecting color-blindness. 
 
 Homocentric Rays (ho-mo-sen'-tric). A conic pen- 
 cil of light-rays. 
 
 Homonymous. (See Diplopia.) 
 
 .Hordeolum (hawr-dee'-o-lum). Sty; inflammation 
 
 V of sebaceous glands of the eyelid. 
 
 Horny Epithelium. Trachomatous conjunctivitis. 
 
 Horopter (ho-rop'-tur) . 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. A fluid element of the eye (Aqueous, 
 
 crystalline lens, and vitreous.) 
 
 Hyaline (hi'-al-in). Glassy. 
 
 Hyalitis (hy-al-i'-tis) . Inflammation of the vitreous 
 humor or hyaloid membrane. 
 
 Hyaloid (hy'-al-oid) . That which resembles glass 
 
 V in its transparent quahties. 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, 
 
\ 
 
 OPTICAL DICTIONARY. 76 
 
 Hyaloid Fossa. The depression in the anterior sur- 
 face of the hyaloid membrane in which the 
 crystalHne lens lies. 
 
 Hyaloid Membrane. The delicate transparent mem- 
 brane which forms a sac and contains the vitreous 
 humor, and forms the suspensory ligaments of 
 the lens and the Zone of Zinn. 
 
 Hydrophthalmia (hy-drof-thal'-mi-ah) , Hydroph- 
 thalmus. 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). A sac or cyst filled with 
 fluid. 
 
 Hyperaesthesia (hi-per-as-the'-si-ah). Over-sensi- 
 tiveness. H. of Retina, over-sensitiveness of the 
 retina. 
 
 Hyperemia (hi-per-e'-me-ah) . A condition where 
 there is an abnormal fulness of the blood-vessels. 
 H. of the eyelids is often a forerunner of inflam- 
 mation. It is usually accompanied by a slight 
 marginal blepharitis and even conjunctivitis, and 
 if these are relieved the hyperemia to a great ex- 
 tent will disappear. 
 
 Hyperkeratosis (hy-per-ker-at-o'-sis) . Hypertrophy 
 of the cornea. 
 
 Hypermetropia (hy-per-me-tro'-pi-ah) (far-sighted) . 
 An error of refraction, where parallel rays 
 of light focus back of the retina with 
 the muscles of accommodation at rest. Sub- 
 divided into three classes — latent, manifest 
 
76 LEWIS POCKET 
 
 and total. Latent h. has no subdivisions; it 
 is hypermetropia that is hidden by cramp of 
 the ciHary 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 be- 
 gins to relax and more, hypermetropia becomes 
 manifest. It may take a week or a year. Mani- 
 fest h. is that part found and corrected 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 his error 
 
 A hypermetropic eye. The heavy lines show tne focus of 
 parallel rays behind the retina. The dotted lines show the 
 effect of accommodation upon the same rays. 
 
 by accommodation, and sees well at all distances. 
 Classes 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. 
 
OPTICAL DICTIONARY. 77 
 
 The correction 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- 
 metropia. 
 
 Hyperopia (hi-per-o'-pe-ah). (See Hypermetropia.) 
 
 \ Hyperphoria (hy-per-f o'-ri-ah) . The tendency of 
 elevation of one visual axis above the other. 
 
 Hyperplasia (hi-per-pla'-ze-ah) . Excessive tissue 
 formation. 
 
 Hypertropia (hy-per-tro'-pi-ah). Elevation of one 
 visual axis above the other. 
 
 Hypertrophy (hy-per'-tro-f y) . An abnormal in- 
 crease in the size of a part or an organ. 
 
 Hyphemia (hi-f e'-me-ah) . Hemorrhage within the 
 eye. 
 
 Hypnogenet'ic. Causing or producing sleep. 
 
 Hypnolepsy (hip'-no-lep-se) . Abnormal sleepiness. 
 
 Hypometropia (hy-po-me-tro'-pi-ah). (See Myopia 
 and Brachymetropia.) 
 
 V Hypophoria (hi-po-f o'-re-ah) . , A tendency of a 
 visual line downward. 
 
79 LEWIS POCKET 
 
 Hypopyon (hi-po'-pe-on) . Pus in the anterioi oiiam- 
 ber of the eye. 
 
 Hypotonia (hi-po-to'-ne-ah). Diminished intra- 
 ocular tension. 
 
 Hypotonus (hi-pot'-o-nus). (See Hypotonia.) 
 
 Hypotony (hi-pot'-o-ne) . (See Hypotonia.) 
 
 Xdentical Points. When the image falls on corre- 
 sponding points on the retinae of the two eyes. 
 
 Iliaqueation (il-lak-we-a'-shun) . The curing of in- 
 growing eyelashes by drawing with a loop. 
 
 Illumination (il-lu-min-a'-shun) . The lighting up of 
 a place or object for inspection. Focal i., when 
 light is brought to a focal point by lens or mirror. 
 Axial Uy 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'-zhun) . An unreal image presented 
 to the mental vision. 
 
 Image (im'-ej). A picture or conception of any- 
 thing real. Aeri^^., image seen as in the air by 
 the ophthalmoscopeSsj Direct i., Erect i., and 
 Virtual i., formed by rays not yet focused. An 
 upright imag^M False i., image formed on the 
 retina of the deviating eye in strabismus. 
 Optical i., an appearance of an object created by 
 refraction or reflection. 
 
 Inad'equacy. Unable to perform' allotted functijn 
 
\ 
 
 OPTICAL DICTIONARY. 79 
 
 m cideiit Ray. The name given to a ray of light 
 before it strikes the second medium. 
 
 Index of Refracting. The refracting or bending 
 y 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 
 the vitreous humor, 1.33. 
 
 i Infinite Distance. When rays of light proceed from 
 V a distance of twenty feet or more they are con- 
 sidered parallel, and are said to come from in- 
 finity. 
 
 Inflammation (in-flam-ma'-shun). A diseased con- 
 dition characterized by redness, pain, heat, and 
 swelling. Traumatic i., that which follows a 
 wound or injury „ 
 
 Infraduction, Deorsumvergence. The power of the 
 inferior rectus muscles. 
 
 Infraorbital (in-f ra-or'-bi-tal) . Situated beneath 
 the orbit. 
 
 J[nstrunients and their uses. 
 
 N^ Amblyoscope — An instrument to stimulate, ex- 
 ercise, and develop the fusion faculty in strabis- 
 mus, or squinting patients. 
 
 Color Test (Holmgren's) — A set of worsteds, 
 consisting of various shades and tints, for testing 
 color-blindness. 
 
80 LEWIS POCKET 
 
 Deviometer — An instrument for determining 
 the degree of deviation in strabismus, or squint. 
 
 Keratometer — (See Ophthalmometer.) 
 
 Latest Optometer — An instrument combining 
 the advantages of a fixed and revolving-cell trial 
 frame, Stevens Phorometer, Rotary Prism, and 
 Maddox Multiple Rod. 
 
 Ophthalmoscope — An instrument with which 
 the interior of the eye may be examined. Also 
 the dioptric and pathological states may be deter- 
 mined. There are many different kinds of oph- 
 thalmoscopes; 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 combined ophthalmo- 
 scope and retinoscope, a combined instrument 
 for indirect ophthalmoscopy and for retinos- 
 copy. 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 refraction 
 s 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 
 patient. 
 
 Savage Monocular Phorometer and Cyclo- 
 Phorometer — Two instruments which together 
 
OPTICAL DICTIONARY. 81 
 
 ixiake a complete appliance for measuring all of 
 the muscles of the eye. 
 
 Self- Luminous Retinoscope — An instrument for 
 retinoscopy, self -lumina ted. 
 
 Skiascope — A frame with a series of plus and 
 minus spherical lenses, to be used in place of test 
 frame and lenses when refracting a patient by 
 retinoscopy. 
 
 Stevens Phorometer — An instrument for meas- 
 uring muscular imbalance. 
 
 Stigmatometer — An instrument for testing re- 
 fraction of the eye by the objective method. 
 Also a complete ophthalmoscope for the direct 
 examination. 
 
 InsuflBlciency. Incapacity of normal action within 
 
 the eye. 
 
 Intercilium (in-ter-sil'-e-um) . 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, Sturm's, or Focal i. In astigmatism, is 
 the distance between the two foci, at which the 
 principal 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. 
 Ir'idal. Pertaining to the iris. 
 
82 LEWIS POCKE 
 
 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'-tormy) . The operation for re- 
 moving a piece from the iris for the reHef of ten- 
 sion of the eyeball in the case of glaucoma, thus 
 producing an artificial pupil. 
 
 f ridencleisis (ir-id-en-cli'-sis) . An operation for dis- 
 placing 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 become adherent there. 
 
 Irideremia (ir-id-er-e'-mi-ah) . Defect or imperfect 
 condition of the iris. 
 
 Irides (ir'-id-ez). Plural of iris. 
 
 Iridesis (ir-id'-e-sis) . Strangulation of a part of 
 the iris to form an artificial pupil. 
 
 Iridescent Vision. That condition in which vari- 
 ously 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 is 
 completely torn from its periphery. 
 
 Iridocele (i-rid'-o-sele) . Hernial protrusion of a 
 slip of the iris. 
 
 Iridochoroiditis (ir-.id-o-ko-roid-i'-tis). Inflamma- 
 tion of the iris and choroid. 
 
OPTICAL DICTIONARY. 83 
 
 Iridocinesis (ir-id-o-sin-e'-sis). The movement of 
 the iris in contracting and expanding. 
 
 Iridocyclitis (ir-id-o-syc-li'-tis) . 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) . Separation of the 
 iris from the ciliary body. 
 
 Iridodonesis (ir-id-o-do-ne'-sis) . Trembling condi- 
 tion of the iris. 
 
 IridoDcus (ir-id-on'-kus) . A tumor or swelling of 
 the iris. 
 
 Iridoperiphacitis (ir-id-o-per'-i-f a-si'-tis) . Inflamma- 
 tion of the capsule of the lens of the eye. 
 
 Iridoplania (ir-id-o-pla'-ni-ah) . Trembling of the 
 iris; iridodonesis. 
 
 Iridoplegia (ir-id-o-ple'-gi-ah) . 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, some- 
 times without any other symptoms of that dis- 
 ease, 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. 
 
\, 
 
 ^ LEWIS POCKET 
 
 Iridorrhexis (ir-id-or-rhex'-is) . Rupture of the iris. 
 Tearing away of the margin of the iris. 
 
 Iridosclerot'omy. Puncture of the sclerotic and of 
 the edge of the iris. 
 
 Iridotomy (ir-id-ot'-o-my) . The operation whereby 
 an artificial pupil is formed by the natural gaping 
 of a simple incision in the iris. Iridotomy is most 
 useful when the iris has become tightly drawn 
 toward the operation scar by iritis occurring after 
 a cataract has been removed. 
 
 I'ris. That part of the second tunic which is located 
 in front of the crystalhne lens and gives the eye 
 its color and regulates the amount of light which 
 enters. It contains two muscles, the circular (or 
 sphincter), which surrounds the pupil, and is 
 supplied by the third nerve; the radiating muscle 
 (or dilater), which is chiefly supphed by the sym- 
 pathetic. The iris is suspended in the aqueous 
 humor, which fills the space between the cornea 
 and the lens, thus forming the anterior and pos- 
 terior chambers. 
 
 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). 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. ^ 
 
OPTICAL DICTIONARY. 81 
 
 Irregular Astigmatism. (See Astigmatism.) 
 
 Irritant. Causing irritation. 
 
 Ischemia (is-ke'-me-ah). Bloodlessness. 
 
 Ischemia Retinae (is-ke'-me-ah). Diminution oi 
 
 arteries in the retina. 
 
 Isocoria (i-so-co'-ri-ah) . Where the pupils in the 
 two eyes are equal. 
 
 Isometropia (i-so-met-ro'-pi-ah) . The state in which 
 both eyes are alike in their refraction. 
 
 tJ ager's Test Type. The standard type for close 
 print. 
 
 Jeffrey's Symptom. That condition which exists 
 when patient suddenly turns his eyes upward and 
 there is absence of facial contraction; seen in 
 exophthalmic goiter. 
 
 \ 
 
 -ki^eratalgia (ker-at-al'-je-ah). That condition in 
 which there is pain in the cornea. 
 
 Keratectasia (ker-at-ek-ta'-si-ah) . That condition 
 in which the cornea protrudes. 
 
 Keratitis (ker-at-i'-tis) . Inflammation of the cornea. 
 
 Keratocele (ker-at'-o-cele) . Corneal protrusion of 
 Descemet's Membrane. 
 
 Keratoconus (ker-at-o-ko'-nus) . That conditibn in 
 which there is a conical cornea. 
 
86 LEWIS POCKET 
 
 Keratoglobus (ker-at-o-glo'-bus) . A globular pro- 
 trusion of the cornea. 
 
 Keratohelcosis (ker-at-o-hel-ko'-sis) . That condi- 
 tion wherein there is ulceration of the cornea. 
 
 Keratoiri'tis. That condition wherein the cornea 
 and iris are inflamed. 
 
 Keratomalacia (ker-at-o-ma-la'-she-ah) . Softening 
 of the cornea. 
 
 Keratome (ker'-at-om) . A knife for incising the 
 cornea. 
 
 Keratometer (ker-at-om'-e-ter) . An instrument used 
 for measuring the cornea. It is commonly called 
 the ophthalmometer, of which there are several 
 different makes. 
 
 Keraiometry (ker-at-om'-e-try). Measurement of • 
 corneal curves. 
 
 Keratomycosis (ker-at-o-my-ko'-sis) . Fungous dis- 
 ease of the cornea. 
 
 Keratonyxis (ker-at-o-nik'-sis) . Puncture of the 
 cornea. 
 
 Keratoplasty (ker'-at-o-plas-ty) . Plastic surgery of 
 the cornea. 
 
 Keratoscope (ker'-at-o-scope). Instrument for ex- 
 amining the cornea. 
 
 Keratoscopy (ker-at-os'-ko-pe). Examination of the 
 cornea with a keratoscope. Skiascopy. 
 
 Kerectomy (ke-rek'-to-me). Removal of part of tb^ 
 cornea. 
 
OPTICAL DICTIONARY 8V 
 
 Kilometer. One thousand meters. 
 
 Kopiopia or Copiopia (ko-pee-oh'-pee-ah) . (See 
 Asthenopia.) 
 
 Koreetomia or Corectomia (ko-rek-to'-mee-ah) . The 
 • operation for artificial pupil by removal of a part 
 of the iris. 
 
 Korectopia (kor-ek-to'pe-ah) . Displacement of the 
 pupil. 
 
 Koroscopy (ko-ros'-ko-pee) . (See Retinoscopy.) 
 
 \^ 
 
 -Liachrymal Apparatus. Consists of the lachrymal 
 gland which secretes the tears and the exsecretory 
 ducts which convey the fluid to the surface of the 
 eye. This fluid after passing over the eye run? 
 
 . through the puncta into the lachrymal canal, 
 then to the lachrymal sac and along the nasal 
 duct into the cavity of the nose. 
 
 Lachrymal (lak'-rim-al) . Pertaining to tears. 
 
 Lachrymation (lak-rim-a'-shun) . The secretion and 
 discharge of tears. 
 
88 LEWIS POCKET 
 
 Lachrymotomy (lak-rim-ot'-o-my) . Operation for in- 
 cision of lacrimal duct or sac. 
 
 Lacrimal, Lacrymai. (Same as Lachrymal.) 
 
 Lacu'nar Orbitae. The roof of the orbit of the eye. 
 
 ^ La^cus Lacrima'lis. The triangular space at the 
 inner canthus between the two eyelids. 
 
 Lagophthalmus (lag-of-thar-mus) . That, condition 
 in which it is impossible to close the eyes. 
 
 Lakus. The small circular portion at the nasal side 
 of the opening between the eyelids. 
 
 Lamina (lam'-in-a) . A layer consisting of a flat, 
 thin membrane. 
 
 N^' 
 
 I^amina Cribrosa (lam'-in-a crib-ro'-sa) . The per- 
 forated area in the sclerotic through which the 
 optic nerve fibers pass to form the retina. 
 
 Lamina Fus'ca. 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, BerHn, 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 investiga- 
 tions in his specialty have been distinguished by 
 their originality. Among his works are ^^On the 
 Retina,'^ **A Manual of Ophthalmoscopy,*^ pub- 
 lished in French, EngUsh, German, and Spanish, 
 *'The Refraction and Accommodation of the Eye." 
 
OPTICAL DICTIONARY. 89 
 
 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 eyelids. 
 
 Latent (la'-tent). That which is not apparent or 
 manifest. (See Hypermetropia.) 
 
 Layer. A stratum having a certain amount of thick- 
 ness and serving the purpose of a covering. 
 
 Leber's Disease (La'-berz). Atrophy of the optic 
 nerve, which is hereditary. 
 
 Lema (le'-ma). The dry, hard, yellowish incrusta- 
 tions which collect in the inner canthus. 
 
 Lens. The term lens w^s first applied to any trans- 
 y parent refracting body which had two spherical 
 surfaces, on account of its resemblance to a vege- 
 table known as a lentil. A lens is a transparent 
 substance, crown or flint glass chiefly, through 
 which an object may appear to be increased or 
 decreased in size, and may have either convex or 
 concave spherical or cylindrical surfaces. There 
 are six varieties of spherical lenses — three plus 
 and three minus — all of which can be made the 
 same dioptric 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 thinniest at their centers. A plus sphere wil) 
 refract the same in all its meridians and converge 
 parallel rays to a point or focus, while a minus 
 sphere will diverge parallel rays from a point. 
 
90 
 
 LEWIS POCKET 
 
 The different forms of plus and minus spLorical 
 lenses are here represented: 
 
 A 
 
 V 
 
 A. Piano Convex. 
 
 B. Biconvex. 
 
 C. Periscopic Convex. 
 
 D. Piano Concave. 
 
 E. Biconcave. 
 
 F. Periscopic Concave. 
 
 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 refrac- 
 tion. A secondary axis is any line which crosses 
 the principal axis at the optical center of a lens. 
 It is not a straight line, but a refracted one, and 
 on emerging takes a direction parallel to that 
 which it would have pursued had it not been 
 interrupted by the lens. Cylindrical 1., 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. Crystalline 1., the lens of the eye 
 which resembles a crystal. A transparent double 
 convex lens situated in its capsule behind the 
 pupil between the aqueous and vitreous humor, 
 and when in a state of rest has a focal strength 
 of from plus 19 to plus 20 diopters. Compound 1., 
 a lens consisting of two or more lenses made up 
 
OPTICAL DICTIONARY. 91 
 
 together, such as a sphere and a cylinder. Toric 
 1., a lens with power in all meridians, but of differ- 
 ent amounts on the same side, usually made extra 
 deep periscopic. Periscopic 1., a lens having a 
 convex and concave surface. Achromatic 1., 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 re- 
 fractive power, but of equal dispersive power, and 
 overcomes chromatic aberration. Aplanatic 1. 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 instruments. Bifocal 1. (see Bifocal). 
 Lenticular 1. 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 1., a lens with two elements 
 a sphere and a prism, so arranged that the amount 
 of accommodation and convergence should ex- 
 actly correspond. 
 
 Lens Capsule. A transparent, highly elastic and 
 brittle membrane 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. 
 
92 LEWIS POCKET 
 
 Lenticonus (len-tik-o'-nus) . Exaggerated curva- 
 ture of the crystalline lens. 
 
 Lenticular Astigmatism. (See Astigmatism.) 
 
 Lenticular Ganglion (len-tik'-u-Jar gang'-gle-on) . A 
 small reddish body near the back part of the 
 orbit, between the optic nerve and the external 
 rectus muscle. 
 
 Leucoma (lew-ko'-mah). (See Leukoma.) 
 
 Leukoma (leu-ko'-ma). White corneal opacity. Al- 
 bugo. 
 
 Le'sion, Any hurt, wound, or local degeneration. 
 
 Levator Palpebra Muscle (le-va'-tor pal'-pe-bra 
 mus'-l). (See Muscles.) 
 
 Ligament (lig'-a-ment) . A tough band of connec- 
 tive tissue, the purpose of which is to connect the 
 bones together or surround them as a capsule. 
 There are several ligaments concerned in the 
 anatomy of the eye. Ciliary Ligament, Palpebral 
 Ligament, External Palpebral Ligament, Internal 
 Palpebral Ligament, Suspensory Ligament or 
 Zone of Zinn, Ligament of Zinn. The Ciliary 
 1., or circle (annulus albidus), is the bond 
 of union between the external 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 distribu- 
 tion, and it receives the anterior ciliary arteries 
 through the anterior margin of the sclerotic. 
 A minute vascular canal is situated within the 
 ciliary ligament, called the ciliary canal, or the 
 
OPTICAL DICTIONARY. 93 
 
 Canal of Fontana, from its discoverer. The 
 Palpebral 1. joins the cartilage of the lids 
 to the orbit the same as the tarsal ligament. 
 The External Palpebral 1. unites the lid to the 
 outer edges of the orbit. The Internal Palpebral 
 1. covers an area including the upper maxilla 
 to the inner margin of the lid. The Suspensory 
 I., 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 arises the four recti muscles and the 
 superior oblique. 
 
 Light. Light is that physical force which, acting 
 upon the sensitive elements of the retina, excites 
 in the mind the impression of vision (or vibrations 
 of ether), and is made up of rays, beams, and 
 pencils. 
 
 A Ray is the smallest visible line of light. 
 
 A Beam is ti collection or bundle of parallel 
 rays. 
 
 A Pencil is a number of converging or 
 diverging 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 twenty feet or farther away are so nearly 
 so that the difference can only be mathematically 
 expressed, and for the purposes of optics are con- 
 sidered 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 
 
94 LEWIS POCKET 
 
 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 they 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 imagina- 
 tion. 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 short- 
 est 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 twenty 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 twenty 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 considered to have 
 none. This is known as a plane wave. 
 
 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 eo metre. Now, as the one and 
 same wave moves on, it loses its curvature; thus 
 
OPTICAL DICTIONARY^ 95 
 
 when it has traveled one inch from its center its 
 curvature is less, or — 40, and at two inches, 
 — 20; three inches, — 13; four inches, — 10; five 
 inches, — 8; twenty inches, — 2; forty inches, 
 — 1; eighty inches, — .50 (these figures are the 
 fractional parts of a metre, 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 — 1, and a 1-D. lens has a focal length 
 of forty inches. A wave that has traveled twenty 
 inches from a point is known as a — 2, while a 
 2-D. lens would focus at twenty inches. For 
 instance, 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-D. Then 
 you would say that the curve is — 3 if it is 
 going from, a point, but if going to a point, + 3. 
 You will notice that in referring to a metre 
 it is spoken of as forty inches. There is a differ- 
 ence between the two, yet it is near enough for 
 our purpose, and saves the trouble and incon- 
 venience 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 artificial 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 
 
96 LEWIS POCKET 
 
 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 media, such as glass, its speed is retarded, 
 and it regains its former speed on emerging into 
 air again. 
 
 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: 
 
3^ 
 
 .o^- 
 
 
 
 %'^ 
 
D 
 
 i 
 
 
 i- 
 
 / 
 / 
 
 -^ 
 
 .CP 
 
 
 ttOQ 
 
 I- 
 
 ? O 
 
 Si 
 
 
 .^ 
 
 A. 
 
 ^•^ 
 
 o 
 
 o 
 
 SB 
 
 go* 
 
 si 
 
 ^& 
 
 BS 
 
 is 
 
 §5* 
 
 §1- 
 
 (DP* 
 
 
 o 
 
 
 •s 
 
 JO 
 
tB i::^j^ ^ 
 
 p o ^ ^ ^ Q ^P" 
 
 §-§3cL^-h8 
 
 , ca3 "' a (D *^ ^„ 
 
 
 S o 1^ ^trg a-i2 
 
 S erg so P B^P S^ 
 |w ?;-clJ? p-«> p 
 
 « 2 S 2 P ^-tj 
 
 §8:3 CD? 
 P25 
 
 * ^ cf-2 r^p'p "* 
 
 rrsl ^ '^ 2 <P C I 
 
102 LEWIS POCKET 
 
 lAsht Area on the Face. The term used to desig- 
 nate the Hght upon the face when the beam of 
 hght from the retinoscope is directed upon the 
 eye under observation. 
 
 Light Area in Pupil. The Hght seen in the pupil 
 of an eye under observation with the retinoscope, 
 caused by the reflex from the retina. Its char- 
 acter and relative movement indicate the re- 
 fractive condition of the eye. 
 
 Limbus Cornea (lim'-bus). (Border line.) The 
 region where the cornea and sclerotic join. 
 
 Limit Angle. (See Critical Angle.) 
 
 Limitans (lim'-it-ans) . That which limits or bounds 
 a body or organ. 
 
 Line of Fixation. A line which connects the object 
 looked at with the macula lutea through the 
 nodal point of the eye. 
 
 Line of Vision. The line which connects the ob- 
 ject looked at with the fovea centralis (visual 
 axis) . 
 
 Lippitudo (lip-pi-tu'-do) . An inflammation of the 
 margins of the eyelids. 
 
 V Liquor Morgagni. A small quantity of fluid between 
 the lens and its capsule. 
 
 Logadectomy (log-ad-ek'-to-my). A removal of a 
 part of the conjunctiva by means of a sharp knife. 
 
 Logades (log'-ad-ees) . The first coat or tunic of the 
 eye. 
 
 Loimophthal^mia. Contagious ophthalmia. 
 
OPTICAL DICTIONARY. . 103 
 
 Long-Sightedness. (See Hyperopia.) 
 
 Lorgnette (lorn-yetO- Double eye-glasses attached 
 to a handle. This term is often applied to opera- 
 glasses. 
 
 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) . That condi- 
 tion in which the eye is turned from parallelism. 
 (Strasbismus; Heterotropia.) 
 
 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. 
 
 S^ Luxation (luk-sa'-shun) of Lens. That condition 
 where the crystalline lens is dislocated. 
 
 iMacropsia (mak-rop'-si-ah). That condition of an 
 eye in which objects appear larger than they 
 really are. 
 
 Macroscopic (mak-ro-scop'-ic). That which may 
 be seen with the naked eye. 
 
 Macula Lutea (mak'-yu-lah lew'-te-ah). Also known 
 y as che yellow spot or most sensitive spot of the 
 retina, situated on the temple side. 
 
104 LEWIS POCKET 
 
 Madarosis (mad-ur-o'-sis). That condition in which 
 the eyelashes are permanently destroyed. 
 
 Maddox Rod. 
 
 Maddox Rod. An opaque disc with a slit through 
 the center. Over this slit is placed a glass rod or 
 cylinder. In looking through this rod at a small 
 round light, it causes the light to look like a long 
 streak. This rod is used for testing muscular 
 insufficiency. Before testing for muscular im- 
 balance 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 
 tissues of the eye, by means of a magnet. 
 
 Magnify (mag'-ni-f y) . To render an apparent in- 
 crease in the size of an object. 
 
 Malacia (mal-a'-se-ah) . Morbid softening of tissue. 
 
OPTICAL DICTIONARY. 105 
 
 Malacocataracta (mal-ak-o-kat-ar-ak'-tah). A soft 
 cataract which forms in the c.ystaUine lens of a 
 person under the fortieth year. This form of 
 cataract is usually the result of injury. 
 
 Malaxation (mal-ax-a'-shun). A rubbing or knead- 
 ing of the eyeball. 
 
 Malignant (mal-ig'-nant). Fatal. 
 
 Malingerer. One who pretends to have a defect of- 
 vision or some other function to evade duty. 
 
 Marginal Keratitis (mar'-jin-al ker-at-i'-tis) . A dis- 
 ease of an inflammatory nature which occurs 
 usually in elderly people. The inflammation ex- 
 tends around the rim of the cornea. If the 
 process continues the cornea is invaded by a 
 densely vascular, superiicially ulcerated, and 
 yet thickened zone. 
 
 Marmarygea (mar-mar'-ij-e-a). Appearance of 
 sparks before the eyes. 
 
 Mature (ma-tur'). Fully developed; ripe. 
 
 Media. The refracting humors of the eye. Opti- 
 cally, media is the plural of medium. 
 
 Medium. Intervening body or quantity. The diop- 
 tric media of the eye consist of the cornea, aque- 
 ous humor, crystalline lens, and vitreous humor. 
 
 Megalocornea (meg-al-o-kor'-ne-ah) . That condi- 
 tion in which there is bulging of the cornea. 
 
 Megalopia (meg-al-o'-pi-ah). (See Macropsia.) 
 
106 
 
 LEWIS POCKET 
 
 Megalopsia (meg-al-op'-si-ah) . That condition of 
 the eye in which objects appear larger than they 
 really are. 
 
 Meg'aloscope. A large magnifying lens. 
 
 Megascope (meg'-a-skope) . A microscope for ex- 
 amining large objects. 
 
 Megophthalmus (meg-of-thar-mus) . That condi- 
 tion in which the eye is abnormally large. 
 
 ANATOMY OP LIDB. 
 
 No. 1. Melhomian Glands. No. 5. 
 No. 2. Puncta Lachrymalia. No. 6. 
 Nos. 3 and 4. Lachrymal Oanals. 
 
 Orbicularis Muscles. 
 Lachrymal Glands, 
 
 Meibomian Glands (mi-bo'-me-an). A variety of 
 \r 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, 
 
V 
 
 OPTICAL DICTIONARY. 107 
 
 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 in preventing friction between the eyeball 
 and lids, and at the same time prevents the cornea 
 from becoming dry so quickly. 
 
 Mel'anin. A dark pigment from choroid, hair, and 
 other dark tissues. 
 
 Melasma Palpebrarum (mel-as'-ma pal-pe-bra'-rum) . 
 A discoloration of the eyelid, which occurs fre- 
 quently in pregnant women. 
 
 Membrana Capsularis. That portion of the arteria 
 centralis, which forms a vascular network and 
 coats the posterior surface of the lens. 
 
 Membrana Pupillaris (mem-bra'-na) . A membrane 
 covering the pupil in fetal life. This sometimes 
 fails to disappear. 
 
 Membrane (mem'-bran). A thin tissue covering 
 some surface or organ. 
 
 Membrane Nictitating. That which is sometimes 
 called the third eyelid, to be seen in various 
 animals. 
 
 Meniscus Glasses (men-is'-kus) . (Or Periscopic.) 
 Glasses that refract at some distance from the 
 center the same as at the center, so that one can 
 see obliquely through them. Minus on one side 
 and convex on the other. Convexo concave. 
 
 Menotyphlosis (men-o-tyf-lo'-sis) . A condition of 
 the eye in which tr^re is diminution of vision 
 during night. 
 
i08 LEWIS POCKET 
 
 Mcramaurosis (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) . A meridian of a circle is 
 any one of its several diameters. A meridian of 
 a lens is any line crossing its surface over its 
 optical center. A meridian of the cornea is any 
 line crossing its surface through its anterior pole. 
 A circle describes 360 degrees, one-half of which, 
 or 180 degrees, is marked on trial frame. and 
 180 are generally found in the horizontal, 90 
 describes the vertical. On the clock-dial they 
 are numbered from left to right, and on trial 
 frame from the right to the left. The figures 
 on trial frame correspond with clock-dial when 
 they are face to face. 
 
 Meropia (mer-o'-pi-ah). (See Amblyopia.) 
 
 Mesoropter (mes-o-rop'-ter). The position of eyes 
 in state of absolute rest. 
 
 Metamorphopsia (met-am-or-fop'-si-ah). That con- 
 dition of the eye in which objects appear distorted. 
 
 Vi Meter Angle. An angle formed by the visual axes 
 of the two eyes looking at a point one metre 
 distant. 
 
 Metre Lens. A lens that will focus parallel rays at 
 a distance of one metre. 
 
 Metric Curve. A curve that has a radius of one 
 
 metre. 
 
 Microblepharia (mi-kro-blef-a'-ri-ah). A very nar- 
 row and thin eyelid. 
 
OPTICAL DICTIONARY 109 
 
 Microcornia (mi-kro-kor'-ne-ah) . A small cornea. 
 
 Microlentia (mi-kro-len'-ti-ah) . A very small crys- 
 talline lens. 
 
 Micrometer. An instrument which is used for mak- 
 ing measurements of very small bodies. 
 
 Micropsia (my-krop' see-ah). That condition of 
 the eye in which objects appear smaller than they 
 really are. 
 
 Microphthalmia (my-krof-thal'-mee-ah) . Abnor- 
 mally small eyes. 
 
 Microscope (mi'-kro-scope). An optical instrument 
 used for examing minute objects. 
 
 Milium. A small elevation, on the skin of' the eye- 
 lid, filled with a greasy secretion. 
 
 Milphae (mil'-phae). A morbid condition in which 
 the eyelashes drop out. 
 
 Milphosis (mil-fo'-sis). That condition in which the 
 eyebrows as well as the eyelashes have fallen out. 
 
 Minus. Minus lenses, same as concave. 
 
 V Miosis (mi-o'-sis). Excessive contraction of the 
 pupil. 
 
 Miotic (mi-otMc). Any agent or medicine which 
 causes the pupil to contract. 
 
 Mirror. An instrument of regular reflection, thus 
 capable of creating images. 
 
 Monoblepsia (mon-o-blep'-si-ah). Blindness to all 
 colors but one. 
 
no LEWIS POCKET 
 
 Monocle (mon'-o-kl). A large round glass worn 
 within the socket of either eye. 
 
 Monocular (mon-ok'-u-lar). Having one eye only. 
 Monocular vision is that condition where the 
 patient has vision in one eye only. 
 
 Moon-Blindness. Amblyopia caused by having the 
 eyes exposed to the full glare of the moon for 
 considerable time. 
 
 Monops (mon'-ops). A foetus with but one eye. 
 
 Motor. 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 
 muscles. 
 
 Mucocele (mu'-ko-sele). Distention of the lachry- 
 mal sac, chronic thickening of the Hning mem- 
 brane, and increased secretion of mucus. The 
 mucus may be clear or turbid. Any tumor con- 
 taining mucus. 
 
 \ Muscae Volitantes (mus'-cae vol-i-tan'-tes) . Small 
 Y floating bodies, resembling sticks, etc., which 
 niove about in the field of vision, but do not ac- 
 tually cross the fixation point, and never inter- 
 fere with sight. They are usually seen against 
 some bright object. They depend upon minute 
 changes in the vitreous, which are present in 
 nearly all eyes. They vary, or seem to vary, 
 greatly with the health and state of the circula- 
 tion, but are of no real importance. They are 
 most abundant and troublesome in myopic eyes. 
 
OPTICAL DICTIONARY. Ul 
 
 tyiUBcles (Eye;. There are six extrinsic muscles tnat 
 \ move the eyeball, namely: 
 
 Internal Rectus Muscle turns the eye in, 
 and is supplied by the third cranial or motor 
 oculi nerve. 
 
 Superior Rectus Muscle turns the eye up, 
 and is supplied by the third cranial or motor 
 oculi nerve. 
 
 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 
 nerve. 
 
 Superior Oblique Muscle rolls the eye on its 
 optic axis, turning the back part of the eye in- 
 ward and upward, while the front part moves 
 down and out, and is supplied by the fourth 
 cranial or patheticus nerve. 
 
 The ciUary muscles are inside the eyeballs, and 
 are used for accommodating only. They are 
 supplied by the third nerve. 
 
 Th« orbicularis palpebrarum muscle closes the 
 lids, and is supplied by the seventh, or facial 
 nerve. (One of the muscles of expression.) 
 
 The levator palpebra superioris lifts the lids, 
 and is fed by a branch of the third cranial nerve. 
 
 The sphincter muscle which closes the pupil is 
 supplied by the third nerve. 
 
112 
 
 LEWIS POCKET 
 
 The radiating muscles of the iris which dilate 
 the pupil are supplied by the sympathetic nerve. 
 
 Tensor tarsi compresses the lachrymal sac and 
 pulls the puncta against the eyeball. Supplied 
 by the seventh cranial nerve. 
 
OPTICAL DICTIONARY. 
 
 113 
 
 Corrugator supercilii draws eyebrow down and 
 inward, and is supplied by the seventh facial 
 nerve. 
 
 Pyramidalis nasi. This muscle depresses the 
 eyebrow. Supplied by the seventh facial nerve. 
 
 Cut showing the Extrinsic Muscle. 
 
114 LEWIS POCKET 
 
 Muscular Asthenopia. (See Asthenopia.) 
 
 Muscular Imbalance. It is generally agreed by the 
 authorities of today that ametropia is responsible 
 for 90 per cent of Muscular Imbalance. For this 
 reason it is considered advisable to always correct 
 any ametropia that may be present, and have the 
 patient wear the correction for at least six weeks. 
 At the end of this time, should any muscular im- 
 balance 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. 
 
 Mycophthalmia (me-kof-thal'-mi-ah) . Inflammation 
 of the conjunctiva, caused by a spongy growth. 
 
 Mydriasis (mid-ri'-as-is). Dilatation of the pupil, 
 caused by the use of atropine or other mydriatics, 
 or paralysis of the motor oculi nerve. 
 
 Mydriatic (mid-ri-at'-ic). A drug that dilates the 
 pupil. 
 
 Myiocephalon (my-i-o-sef '-al-on) . A small protru- 
 sion of the iris through a perforation of the cornea. 
 
 Myodesopsia. (See Muscae Volitantes,) 
 
 Myope (my'-ope). A nearrsighted person. 
 
 \^ Myopia (my-o'-pi-ah). Same as brachymetropia and 
 hypometropia. A visual defect which causes 
 parallel rays of light to focus in front of the retina, 
 with the muscles of accommodation at rest. The! I 
 
OPTICAL DICTIONARY. 115 
 
 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 disap- 
 pear under the influence of atropine. 
 
 These cuts havejjnot been made'with mathematical precision, but 
 are merely intended to roughly exemplify the principle in- 
 volved. The above illustrates 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 indistinct. 
 
 Bonders prcnounced every highly myopic eye 
 a diseased eye, but of late years it has been shown 
 that this remark is liable to convey a false mean- 
 ing. 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 expect to obtain 
 perfect vision by proper lenses, and look for varl 
 cus pathological conditions. 
 
116 LEWIS POCKET 
 
 Symptoms. The patient sees distant objects 
 badly and near objects well. The pupils are 
 usually large, and as presbyopia advances 
 they contract. The eyes look prominent 
 and the patient complains of fatigue, pain, 
 and intolerance of light. All of these symptoms 
 will pass away when the right correction 
 is worn. The cili?iry muscle is 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 Myopia. 
 
 r 
 
 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 allowing 
 the sclerotic to show through. Found in high 
 degrees of myopia. 
 
 Myosis (my-o'-sis). Abnormal contraction of the 
 pupil. (Same as miosis.) 
 
 Myotic. An agent that will contract the pupil, such 
 as eserin, pilocarpine, etc. 
 
 Myotomy (mi-ot'-o-me) . The dissection or divi- 
 sion of muscles. 
 
OPTICAL DICTIONARY. 117' 
 
 IN asal Duct. That part of the tear duct below 
 lachrymal sac, and opening into the nose. 
 
 \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' refraction 
 is adjusted when the full amount of accommoda- 
 tion is being used. 
 
 Near-Sight. (See Myopia.) 
 
 Neb'ula. Slight corneal opacity. 
 
 Needling (needMing). An operation for soft cata- 
 ract. The lens capsule is needled, and the aqueous 
 ^ allowed to absorb the lens. 
 
 Negative (neg'-a-tive) . The opposite of positive. 
 The negative surface of a periscopic lens is the 
 concave surface. 
 
 Neotocophthalmia (ne-ot-ok-of-thal'-mi-ah) . (See 
 Ophthalmia Neonatorum.) 
 
 Nephablepsia (nef-ab-lep'-si-ah). (See Snow-Blind- 
 ness.) 
 
 Nephelopia (nef-el-o'-pi-ah) . A diminutior. of vision, 
 caused by a cloudiness of the transparent parts 
 of the eye. 
 
118 LEWIS POCKET 
 
 Nephritic Retinitis (nee-f rif-ik) . A form of inflam- 
 mation of the retina associated with Bright's dis- 
 ease of the kidneys, characterized by white 
 streaks along the course of the blood-vessels. 
 
 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 
 
 3. Motor Oculi, motor nerve for eye muscles. 
 
 4. Patheticus, motor nerve for superior oblique 
 muscle. 
 
 5. Trigeminus, sensory, motion, and taste. 
 
 6. Abducens, motor nerve for external rectus 
 muscle. 
 
 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. Hypo Glossal, 
 
 Motor n., one which contains wholly motor 
 fibers. N. center, a group of cells which consist 
 of gray matter and have a common function. 
 Mixed n., a nerve which is both motor and sensory. 
 N. head, the optic disc or papilla. Sensory n., 
 any nerve which transmits sensations or im- 
 pulses. Sympathetic n,, any nerve of the sympa- 
 thetic system. 
 
 Nerve (Optic). The nerve that transmits retinal 
 sensations to the centers of perception in the 
 brain, there to be translated into sight. The 
 
View of the Eye from the Temporal side 
 with part of the Orbit Removed. 
 
 1. Eyeball with part of external rectus 
 
 muscle. 
 
 2. Superior Maxilla. 
 
 3. Third pair (or Motor Oculi) nerves. 
 
 They are distributed to all the 
 muscles of the eye except the Supe- 
 rior Oblique, External Rectus and 
 the Dilator Muscles of the Iris. 
 
 4. Fourth pair of Nerves, feeding Superior 
 
 Oblique Muscles. 
 
 6. Sixth pair of Nerves, feeding External 
 Rectus. 
 
 8. Ciliary Nerves entering the globe. 
 
OPTICAL DICTIONARY 119 
 
 nervous system is a system of connection and 
 communication by which the different organs, 
 vessels, and various parts of the body are brought 
 into direct relation with each other and with the 
 mind, and the various organs stimulated to 
 harmonious or alternating action. It consists 
 of the brain and spinal cord, called the central 
 nervous system, which controls the voluntary 
 actions of the body, sometimes called the nerves 
 of animal life, and is directly connected with the 
 sympathetic nerves, w^hich 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 cen- 
 tral, 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 oblongata, 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, stimulation of w^hich cause 
 dilatation of the blood-vessels and an increased 
 amount of blood to a part, and vaso constrictors, 
 stimulation of which cause constriction or con- 
 traction 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 nly 
 in the past few years been known to any extent, 
 
120 LEWIS POCKET 
 
 the vaso motor center being discovered by 
 Schiff in 1855, and more accurately localized 
 by Ludwig in 1871. The cranial nerves are 
 those that have their apparent origin in the 
 cranium. Sommering and other European 
 anatomists name twelve pairs, while WilHs and 
 a few other authors designate only nine pairs, 
 according to the order in which they pass out 
 of the base of the brain. 
 
 Neuritis (neu-ri'-tis) . Inflammation of the optic 
 nerve. 
 
 Neurology (nu-rol'-o-je) . A study of the nervous 
 system. 
 
 Neurodealgia. Pain or excessive sensibility of the 
 retina. 
 
 Neurodeatrophia. Atrophy of the retina. 
 
 Neuroretinitis (neu-ro-ret-in-i'-tis) . Inflammation 
 of the optic nerve and retina. 
 
 Neutralize (neu'-tral-ize). The method of counter- 
 balancing or doing away with power in lenses. 
 In order to det rmine whether a lens is of plus 
 or minus power, hold it up and look at some dis- 
 tant object through it, then move the lens from 
 side to side and if the object appears to move 
 in the opposite direction to the movement 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 movement of the lenses the 
 minus is not strong enough. On the other hand, 
 should the movement be reversed and now the 
 
OPTICAL DICTIONARY. Ul 
 
 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 in- 
 stance, 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, -f2 sphere combined with +1 
 cylinder, axis 90*' is required, then the lens being 
 neutralized is a — 2 sphere combined with — 1 
 cylinder, axis 90^, etc. 
 
 Nictitation (nik-tit-a'-shun) . Involuntary convul- 
 sive twitching of the eyelids. 
 
 Xight-Blindness. (See Hemeralopia.) 
 
 Niphablepsia (nif-ab-lep'-si-ah) . That condition 
 wherein blindness is caused by the glaring reflec- 
 tion of sunlight upon the snow. Snow-blindness. 
 
 No'dal Points. (Or Cardinal Points.) Are two points 
 situated on the optic axis, connecting the centers 
 of curvature of the refracting compound dioptric 
 
system of the eye. The nodal points of the eyo 
 are so close together that they may be considered 
 as one point.* 
 
 Normal. That which conforms 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. Sup- 
 pose, 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. 
 
V 
 
 Nubecula (nu-bek'-u-la) . "Slight cloudiness of the 
 cornea. 
 
 Nuclear Cataract. (See Cataract.) 
 
 Nyctalopia (nyk-tal-o'-pi-ah) . (See Day-Blindness.) 
 
 Nyctotyphlosis (nyk-to-tyf-lo'-sis) . State of blind- 
 ness at night-time. 
 
 Nystagmus (nys-tag'-mus) . Short, jerking move- 
 ments 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 
 attributed to the nystagmus, but, on the con- 
 trarj^, 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. 
 
 Ubfuscation (ob-f us-ka'-shun) . 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 intelligently 
 impressed and appreciated by the brain. 
 
 Objective (ob-jek'-tive). Symptoms observed by 
 operator usually with ophthalmoscope or retino- 
 scope. Symptoms which the refractionist dis- 
 covers by means Oi one or more of his five senses; 
 Objective Examination. An examination cou' 
 ducted independent of the patient's statements. 
 6. g.^ retinoscopy. 
 
124 LEWIS POCKET 
 
 Oblique. ' Slanting; placed in a plane between the 
 horizontal and vertical planes. 
 
 Occlusion of the Pupil (ok-klew'-zhun). Blocking 
 up of the pupil by a membrane. 
 
 Ocular (ok-'u-lar). 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 before 
 the eyes. 
 
 Oculist (ok'-u-list) . A physician and surgeon who 
 has received the degree, ** Doctor of Medicine," and 
 makes a speciality of the eye and its diseases. 
 
 Oculomotor (ok'-yu-loh-moh'-tor). Pertaining to 
 the movements of the eye. 
 
 Oculus (ok'-yu-lus) . 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. An accumulation of pus between the layers 
 of the cornea. 
 
 Opacity (o-pas'-i-ty). A want of transparency. 
 
 Opaque (o-pake'). Impervious to light. Not trans- 
 parent. 
 
OPTICAL DICTIONARY. 125 
 
 Operculum Oculi (o-per-cu'-lum oc'-u-li). The eye- 
 lid. 
 
 Operation (op-er-a'-shun) . An act performed with 
 instruments or by the hands of a surgeon. 
 
 Ophryitis (of-ry-i'-tis). That condition in which the 
 eyebrows are inflamed. 
 
 Ophrys (of'-rys). Eyebrows. 
 
 Ophthalmagra (of-thal'-ma-grah) . A sudden intense 
 pain in the eye, usually rheumatic or gouty in 
 origin. 
 
 Ophthalmalgia (of-thal-mal'-ge-ah) . Sudden vio- 
 lent pain in the eye, not the result of inflamma- 
 tion, but neuralgic in character. 
 
 Ophthalmatrophia (of-thal-mah-tro'-fe-ah). Atrophy 
 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. 
 
 Ophthalmic (of-thar-mic) . That which pertains to 
 the eye. 
 
 Ophthalmitic (of-thai-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) . Inflammation of the 
 eye, more especially the globe with its membranes. 
 
 Ophthalmoblennorrhoea (-blen-ur-ree'-ah). A flow of 
 mucus from the eye. 
 
 Ophthalmocarcinoma (-kahr-si-no'-mah). Cai^cer 
 of the eye. 
 
126 LEWIS POCKET 
 
 Ophthalmocele. (See Stapyloma.) 
 
 Ophthalmocopia (-koh'-pee-ah) . Fatigue of the eyes; 
 Asthenopia. * 
 
 Ophthalmodynia (-din'-e-ah) . Neuralgic pain of the 
 eye. 
 
 Ophthalmography (-mog'-rha-f ee) . A description of 
 
 the eye. 
 
 Ophthalmologist (of-thal-moF-o-gist) . One who 
 practices opthalmology and has taken the degree, 
 ^'Doctor of Medicine." An Oculist. 
 
 Ophthalmology (of-thal-mol'-o-gy) . A study of the 
 eye and its diseases. 
 
 Ophthalmomiaerosis (-ma-kro'-sis) . Enlargement of 
 the eyeballs. 
 
 Ophthalmomalacia (-ma-la'-sha) . That condition in 
 which there is abnormal softness of the eyeball. 
 
 Ophthalmopathy (-mop'-a-thee) . Any disease of the 
 eye. 
 
 Ophthalmophthisis (-mof '-thi-sis) . That condition 
 in which there is wasting of the eyeballs. 
 
 Ophthalmoplegia (-ple'-jah). Paralysis of the 
 ocular muscles of the eye. O. Partial, a form 
 In which only some of the muscles are para- 
 lyzed. O. Progressive, a gradual paralysis of all 
 the muscles of 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, par- 
 alysis of the internal muscles. 
 
OPTICAL DICTIONARY. 127 
 
 Ophthalmoptoma (-mop-to'-mah) . Protrusion of 
 the eyeballs. 
 
 Ophthalmorrhagia (-mor-rha'-gee-ah) . Hemorrh- 
 age from the eye or orbit. 
 
 Ophthalmorrhexis (-mor-rex'-is) . The bursting of 
 the eyeball. 
 
 Ophthalmoscope (of-thar-mo-scope). An instru- 
 ment 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 rever- 
 sible 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 aperture 
 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 ^o 
 far as estimating the refraction of the eye is con- 
 cerned, 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 diseased condition 
 exists in the interior of the eyeball. 
 
128 LEWIS POCKET] 
 
 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 patient's 
 face. We take our seat in front of the patient 
 and hold our ophthalmoscope at the focal dis- 
 tance 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 from the eye will leave it 
 as parallel rays in cases of emmet^opia; as diver- 
 gent rays in hypermetropia; and as convergent 
 rays in myopia. These rays will be brought to 
 a focus by the convex objective glass which we 
 hold close to the eye under examination. 
 
 We direct our patient to look slightly inward 
 while making this examination, in order to bring 
 the optic disc into view. It will be remembered 
 that the optic disc is situated slightly to the 
 
OPTICAL DICTIONARY. 129 
 
 inner or nasal side of the center of the retina, so 
 that when our patient looks slightly inward, the 
 back part of the eye naturally moves outward, 
 bringing the optic disc on a line with our vision. 
 The rays emanating from our patient's eye will 
 be brought to a focus by the convex objective 
 glass. 
 
 In the hypermetropic eye the image of the 
 optic disc will look larger than it does in emme- 
 tropia, because the rays from a hypermetropic 
 eye are divergent, and will consequently be 
 brought to a focus beyond the focal distance of 
 the convex objective glass, and on slightly with- 
 drawing our objective glass we will note that the 
 size of the optic disc decreases. 
 
 It must always be remembered in using this 
 method of examining the eye, that we do not 
 see the back part of the eye itself, but simply an 
 inverted image of the fundus of the eye formed 
 in the air between the objective lens and our 
 own eye. 
 
 In emmetropia the optic disc will look smaller 
 than it does in hypermetropia, and larger than 
 in myopia. On slowly withdrawing the objec- 
 tive lens from the emmetropic eye the optic disc 
 will neither increase nor decrease in size, because 
 the rays which emanate from an emmetropic 
 eye will be parallel, and hence will at all times 
 be brought to a focus exactly at the focal distance 
 of the convex objective glass. 
 
 In myopia the image of the optic disc will 
 Appear smaller than in emmetropia and much 
 smaller than in hypermetropia. On gradually 
 withdrawing the objective glass the optic disc 
 will increase in size. 
 
130 LEWIS POCKET 
 
 In cases of astigmatism the optic disc usually 
 looks oval, and on withdrawing the glass it will 
 increase or decrease more rapidly in one meridian 
 than in one at right angles to it. 
 
 In making the direct ophthalmoscopic exam- 
 ination we also use a concave mirror, and arrange 
 the position of the light similar to that described 
 for making the indirect examination, but in this 
 case we place our own eye very close to that of 
 the patient. We place our ophthalmoscope 
 at a distance of about two inches from the 
 patient's eye, and place our own eye immediately 
 
 behind the perforation in the mirror. It is 
 necessary in this examination that neither the 
 patient nor the operator shall use any accommo- 
 dation whatever, and in order that this may be 
 thoroughly accomplished it is well to place the 
 patient under the influence of atropine, assum- 
 ing that the operator has thorough control of 
 his own accommodation and can suspend it at 
 will. 
 
 Upon throwing the light into the emmetropic 
 eye, we illuminate the retina, and a set of rays 
 immediately starts from each point in our pa- 
 tient's retina and passes out of the eye. Each 
 ray of each set is parallel to the other rays in 
 the same set. Therefore, if the operator be 
 
OPTICAL DICTIONARY. 131 
 
 emmetropic himself he will be able to distinctly 
 see the details of the fundus in the back part of 
 his patient's eye, because the rays leave 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 his 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 fundus. 
 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 accommodation 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 observ- 
 er's emmetropic eye, and hence he will be unable 
 to distinctly see the details of the fundus in his 
 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 pro- 
 duces this result will represent the measure of 
 his patient's hypermetropia. In order that the 
 
IJ2 LEWIS POCKET 
 
 operator may distinctly see the hypermetropic 
 retina, he must use a convex glass strong enough 
 ^ to render parallel the divergent rays which are 
 leaving his patient'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 dis- 
 tinctly see the retina of the myopic eye. The 
 
 glass which accomplishes this result is the meas- 
 ure 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-ves- 
 sels 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 meri- 
 dian which was at first blurred, and thereby dim 
 the meridian which was first seen plainly. The 
 
OPTICAL DICTIONARY. 133 
 
 glass which clears up the meridian 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 opera- 
 tor 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 dioptre, 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 hia 
 patient's fundus, he then knows that his patient 
 has two dioptres of hypermetropia, because one 
 of the three was required to correct his own eye, 
 and likewise if he had been examining 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 dioptres of 
 myopia, because he himself was one dioptre 
 hypermetropic. 
 
 Ophthalmostat (of-thal'-mo-stat) . An eye-speculum. 
 
 Ophthalmula (of-thal'-mu-lah). A cicatrix located 
 upon the eye or its appendages. 
 
 Optic. That which pertains to the science of light,^ 
 and also to the eye itself, together with its func- 
 tions. 
 
 V 
 
 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. 
 
V 
 
 134 LEWIS POCKET 
 
 Optic Nueritis. Inflammation of the optic nerve. 
 Optical. Pertaining to the organ of vision. 
 
 Optical Center. A point on line with the thickest 
 point of a plus sphere or the thinnest point of a 
 minus. A ray of light when passing through the 
 optical center of a lens will always emerge paral- 
 lel to the incident ray or in the same plane. 
 
 Optical Corrections. Lenses that change the direc- 
 tion of light rays entering the eyes to such an ex- 
 tent that the eyes are adapted to receive and 
 focus them upon the retina, creating artificial 
 emmetropic conditions when ametropic condi- 
 tions exist. 
 
 Optic Commissure (kom'-mis-ur). The linking or 
 joining together of the right and left optic nerve. 
 
 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 disc. 
 
 Optic Nerve. The nerve which forms a communica- 
 tion between the brain and the organ of vision 
 It transmits retinal sensations to the centers 
 of perception in the brain, there to be translated 
 into sight. (See cut, page 135.) 
 
 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 the 
 manufacture of optical instruments. 
 
OPTICAL DICTIONARY. 
 
 135 
 
 Optics. That part of the science of physics which 
 deals with the transmission of Hght, the laws of 
 refraction, reflection, and the phenomena of 
 vision. 
 
 Optic Tract. The optic nerve between the visual 
 centers and the optic commissure. 
 
 HEAD OF THE, OPTIC NERVE. 
 
 , Opthalmoscopic view of the Optic Disc. The small excava- 
 tions seen around the center is the Lamina Cribrosa. The 
 Papilla is encircled by the white Scleral Ring (c), also the 
 dark Choroidal Ring marked (d) , 
 
 , Longitudinal Section of Head of Optic Nerve; r, the Retina; 
 b, Optic Excavation and Canal for Central Artery (porus 
 opticus); ch, the Choroid; E, Optic Nerve; e, the narrow 
 interspace which corresponds to the Scleral Ring seen by the 
 Ophthalmoscope; s, Sclerotic; ci. Entrance of short Ciliary 
 Artery. 
 
136 LEWIS POCKET 
 
 Optist (op'-tist). A person skilled in optometry. 
 
 Optogram (op'to-gram). A faint image stamped 
 on the retina for a brief period. 
 
 Optometrist. One who measures the eye's refrac- 
 tion. 
 
 Optometry (op-tom'-e-try) . The science and art of 
 employing the various methods of measuring the 
 optical state of the eye. 
 
 ^ O'ra Serra'ta. The anterior limit or edge of the 
 retina. 
 
 Orbicularis Palpebrarum. The circular muscle of 
 the eyelids. 
 
 Orbi cuius Ciliaris. A zone of about one-sixth of 
 an inch in width. It is directly continuous with 
 the anterior part of the choroid. 
 
 Orbit (or'-bit). The bony socket in which the eye- 
 ball is placed. The orbit is made up of seven 
 bones: the Superior Maxillary, Frontal, Lachry- 
 mal, Palate, Malar, Ethmoid, and Sphenoid. 
 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, leav- 
 ing the eyeballs to be protected by the eyelids in 
 front. 
 
 Orbital (or'-bit-al). Pertaining to the orbit. 
 
 Origin (or'-ij-in). The more fixed end of a muscle; 
 for instance, the end attached to the bone of the 
 orbit. 
 
OPTICAL DICTIONARY. 137 
 
 Orthochromatic (or-tho-chro-mat'-ic) . A term used 
 by photographers denoting that the colors are 
 normal or correct. 
 
 Orthometer (or-thom'-e-ter). An instrument for 
 finding the exact relative protrusion of the two 
 eyeballs. 
 
 \, Orthophoria (-f oh'-ree-ah) . That condition in which 
 the eyes are properly placed with respect to each 
 other. Perfect muscular balance. 
 
 Orthoptic (or-thop'-tic) . Correcting heterophoria, 
 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 tojv^ard 
 the apex of the prism in order to see. 
 
 Orthoscope (or'-tho-scope). An instrument for 
 neutralizing the refraction of the cornea by ex- 
 amining it through water. 
 
 Orthoscopic Lenses. A lens with two elements — a 
 sphere and a prism — so arranged that the amount 
 of accommodation and convergence should exactly 
 correspond. 
 
 Orthotropia (or-tho-tro'-piah). Perfect binocular 
 fixation. 
 
 O. S. (Oculus Sinister). Left eye. 
 
 O. U. (Ocular Unati). Both eyes. 
 
 Oxyopia (ox-y-o'-pi-ah). That condition in v/hich 
 the sight is abnormally acute. 
 
138 LEWIS POCKET 
 
 Jr achyblepharon (pach-y-blef-ar'-on) . That condi- 
 tion in which the eyeUds have become thickened. 
 
 Palpebra (pal'-pe-brah) . The eyelid. 
 
 Palpebral (pal'-pe-bral) . That which relates to the 
 eyelid. 
 
 Palpebral Fissure (pal'-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. 
 
 Palpebritis (pal-pe-bri'-tis) . An inflammation of 
 the eyelids. 
 
 Pannus (pan'-nus) . Pannus consists of the new for- 
 mation of a tissue resembling granulations directly 
 beneath the epithelium of the cornea. 
 
 Panophthalmia (pan-of-thal'-miah) . An inflamma- 
 tion of the entire eye structure. 
 
 Panophthalmitis (pan-off -thal-mi'-tis) . General in- 
 flammation of the eyeball. 
 
 Pantiscopic. A lens tilted outward at the top. 
 
 Papilla (pap-il'-lah) . A conic elevation observable 
 at the optic-nerve head. P. Lachrymallis, the 
 mound at the inner canthus of the eye pierced 
 by the lachrymal puncta. 
 
 Papillitis (pap-il-li'-tis) . That condition in which 
 there is an inflammation of the optic disc or 
 papilla. 
 
 Papilloretinitis (pap-il-lo-ret-in-i'-tis) . Inflamma- 
 tion of the optic disc and retina. 
 
OPTICAL DICTIONARY. 139 
 
 Parablep8is (par-ab-lep'-sis) . False vision. 
 
 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 posi- 
 tion. 
 
 Parallel (par'-al-lel) . That which pursues the 
 same direction, but in a separate path. 
 
 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. That condition in which there is a loss 
 of power of voluntary 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, accommodate, 
 the ciliary muscles being in a state of rest. 
 
 Paralyt'ic. Pertaining to, or affected with, paralysis; 
 a person who is affected with paralysis. 
 
 ^Paresis (par'-es-is) . A slight form of paralysis. 
 
 Paropsis (par-op'-sis) . That condition in which the 
 vision is disordered, and may be due to either a 
 false impression being made upon the retina or 
 a disordered condition of the mind. 
 
 Passive. That which is not active; for instance, a 
 muscle that is in a state of rest. 
 
140 LEWIS POCKET 
 
 Pathetic (pa-thet'-ik) . That which pertains to the 
 feelings. The pathetic n^.^iscle is the superior 
 oblique muscle of the eye, which receives its name 
 irom the fact that tho patheticus, or fourth pair 
 
 • of cranial nerves, control its movements. 
 
 Pathological (path-o-log'-i-cal). (See Pathology.) 
 
 Pathology (path-ol'-o-je). The science v/hich haa 
 for its object the knowledge of disease. 
 
 Pediculis Pubis (ped-ik'-u-lus pu'-bis). 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 absence of inflammation and 
 the rather peculiar appearance will lead, in 
 doubtful cases, to the use of a magnifying glass, 
 by which the question will be settled at once. 
 
 Pathologic. Pertaining to diseased conditions. 
 
 Penumbra (pe-num'brah). A partial shadow. 
 
 Perception. The acquiring of impressions 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 receive 
 impressions. 
 
 Perfection Bifocal . (See Bifocal.) 
 
 Pericorneal (per-i-cor -ne-al) . That which is situ- 
 ated iiround the cornea. 
 
 Perichoroidal (-koh-roy'-dul). That which sur- 
 rounds the choroid membrane. 
 
OPTICAL DICTIONARY. 141 
 
 Perimeter (per-im'-e-tur). An instrument for meas- 
 uring the field of vision. 
 
 Periocular (per-e-ok'-u-lar) . That which encircles 
 the eye. 
 
 Perioptic. (See Periocular.) 
 
 Perioptometry (per-e-op-tom'-et-re) . Measurement 
 of the visual acuity of the retinal periphery. 
 
 Periorbita (per-i-or'-bit-a) . That which relates to 
 the lining membrane of the eye socket. 
 
 Periorbital (per-i-or'-bit-al) . Around or about the 
 eye socket. 
 
 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). The tough, fibrous 
 membrane investing a bone. 
 
 Periphacus (per-if-a'-cus). The crystalline lens 
 capsule. 
 
 Periphery (per-if'-er-y). Any outward part or sur- 
 face; for instance, the border of the cornea or 
 crystalline lens. 
 
 V Periscopic (per-is-cop'-ic). A lens having a concave 
 ^ and convex surface. Periscopic lenses are also 
 called miniscus lenses; taken from a Greek word 
 meaning a crescent. (See Lens.) 
 
142 LEWIS POCKET 
 
 Peritomy (per-it'-o-me) . 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). Surrounding a 
 vessel. 
 
 Perivasculi'tis. Inflammation of the sheath of a 
 vessel. This is an increase or a hyperplasia of 
 the connective tissue about the vessels, princi- 
 pally, 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 known as 
 crow's foot; or wrinkles at the outer corner of 
 the eye. 
 
 ^^ Petit's ('anal. The space between the suspensory 
 ligaments in which the edge of the crystalline 
 lens is inserted. 
 
 Phaco (fak'-o). Prefix meaning of, or pertaining 
 to, a lens, especially the crystalline lens. 
 
 Phacitis ^f as-i'-tis) . Inflammation of the crystal- 
 line lens. 
 
 Phacomalacia (f ak-o-mal-a'-she-ah) . A soft cata- 
 ract. 
 
 Phacometer (f a-com'-e-ter) . An instrument for 
 measuring the curvature of lenses, and so deter- 
 mining their refractive power; if they are cylin- 
 drical, will locate their axes. 
 
 Phacosclerosis (f a-ko-sde-ro'-sis) . Hardening of the 
 crystalline lens. 
 
OPTICAL DICTIONARY. 143 
 
 Phacoscope (f a''-ko-scope) . An instrument used for 
 viewing the accommodative changes of the 
 crystaUine lens. 
 
 Phakitis (f a-ki'-tis) . Inflammation of the lens. A 
 supposition exists that the crystalline lens may 
 become inflamed. 
 
 Phantasma (f an'-tas-mah) . A disease of the eye in 
 which imaginary objects are seen. 
 
 Phengophobia (f en-go-f o'-bi-ah) . (See Photophobia.) 
 
 * 
 Phimosis (fi-mo'-sis) Constrictioii. Abnormal small- 
 ness (as of the palpebral fissure). 
 
 Pho'rotone. An instrument for exercising the mus- 
 cles of the eye. 
 
 Phlyctenula (flik-ten'-u-lah). A small vesicle or 
 blister. 
 
 Phlysis (fly'-sis). A corneal ulcer. 
 
 Phoroscope. An instrument in the form of a head- 
 rest, with a clamp attached so that it may be fas- 
 tened to a table, and is used as a fixed trial frame. 
 
 Phosphenes (fos'-feenz). A luminous sensation, 
 caused by pressing on the eyeball. 
 
 Photalgia (fo-tal'-je-ah). Pain in the eye arising 
 from too much light. 
 
 Photochromatic (fo-to-chro-mat'-ic). That which 
 pertains to various colored lights. 
 
 Photodysphoria. (See Photophobia.) 
 
144 LEWIS POCKET 
 
 Photology (fo-tor-o-gy). The science of light. 
 
 Photometer (-tom'-e-tur) . An instrument for test- 
 ing the hght sense. 
 
 Photonosus (f o-ton'-o-sus) . Any disease of the eye 
 which arises from exposure to the glare of light. 
 
 ^ Photophobia (f o-to-f o'-bi-ah) . Intolerance of light. 
 
 Photopsia (f o-top'-si-ah) . 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). A device for 
 measuring sensitiveness to light by showing the 
 smallest amount of light that will allow an object 
 to become visible. 
 
 Phthisis Bulbi (tis'-sis). Shrinkage of the eyeball. 
 
 Physiolog'ical. (See Physiology.) 
 
 Physiology (fiz-e-ol'-o-je). That department of 
 natural science which treats of the organs of the 
 body and their functions. 
 
 Physostigmine (fi-so-stig'-min) . The same as 
 eserin. 
 
 Pigment. The coloring matter in the choroid coat; 
 the iris, etc. 
 
 Pinguecula (ping-gwek'-yu-lah). A small, yellowish 
 elevation, situated in the conjunctiva near the 
 margin of the cornea. Found in old age. 
 
OPTICAL DICTIONARY. 145 
 
 Pin Hole Disc. An opaque disc with a pin hole in 
 the center, found in the trial case. It is placed 
 in the trial frame quite close to the eye under 
 examination. This perforation gives passage 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 pin-hole 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, and lenses will not improve. 
 
 Pink Eye. A catarrhal conjunctivitis. The eye- 
 V 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. 
 
 1 
 Pladaro'sis. That condition where there is a soft 
 tumor on the eyelid. 
 
 Plane. When applied to glass a fiat surface is 
 meant. A plano-concave lens is a lens having 
 one side concave while the other side is fiat. 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). Tending to build up tissues. 
 
 Plica Semilunaris (ply'-kah). A fold of conjunctiva 
 near inner canthus of the eye. 
 
 Point. The far point or punctum remotum is the 
 farthest point at which the eye can see clearly- 
 and distinctly with the accommodation at rest. 
 The near point or punctum proximum is the 
 nearest point at which the eye can see clearly 
 
146 LEWIS POCKET 
 
 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 tho. 
 mirror. This refers to the concave retinoscope. 
 With the flat mirror the movement would b(i 
 directly opposite. P. of Fixation. The point 
 for which accommodation of the eye is adjusted. 
 
 Pole. The summit of a spherical surface. 
 
 Polarimeter. An instrument for measuring tho 
 rotation of polarized 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. 
 
 Polychromatic (pol-y-chro-mat'-ic). Possessing 
 many colors. 
 
 Polycoria (pol-e-ko'-re-ah) . The presence of more 
 than one pupil. 
 
 Polyopia (pol-e-o'-pe-ah). Multiple vision. 
 Pop-Eyedr A large protruding condition of the eyes. 
 
OPTICAL DICTIONARY. Ifl 
 
 Po'rus Opticus. The opening through the lamina 
 cribrosa 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 
 the convex surface. 
 
 Posterior. Behind; back. 
 
 Postocular Neuritis. Inflammation of part of optic 
 nerve behind the eysball. 
 
 Presbyopia (pres-by-o'-pi-ah). When as the result of 
 age the power of accommodation has diminished 
 to such an extent that the eye cannot produce 
 three diopters comfortably, the condition is 
 called presbyopia. The average age when this 
 state of affairs is present is 45, and as age advances 
 the accommodation gradually diminishes and the 
 * presbyopia correspondingly increases. The 
 amount of presbyopia is represented by the differ- 
 ence between the number of diopters of comfort- 
 able accommodation present and three diopters, 
 which must be made good by plus spheres. The 
 presbyope sees well at a distance, providing there is 
 no error of refraction, but has difficulty in main- 
 taining good vision for near work, 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 
 presbyopia it is necessary to test the patient's 
 distant 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 
 
I4S LiJilWitt rUUiVHiT 
 
 in front of his correction until you find the weak- 
 est that will allow comfort in reading. The dis- 
 tance for which the presbyope requires glasses 
 will also vary much according to his or her occu- 
 pation; ordinarily, it is thirteen inches. 
 
 Prescription (pre-scrip'-shun) . The formula for the 
 lenses required by a patient which are desig- 
 nated by technical characters placed on blanks 
 arranged for this purpose. 
 
 Principal Focus. The point where parallel rays 
 of light meet after refraction by a convex spheri- 
 cal lens. 
 
 Principal Meridians. The meridians of greatest and 
 least curvature. 
 
 Prism. When applied to optics is a wedge-shaped 
 V 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 the base. It is used in making tests 
 for muscular insufficiencies, and sometimes pre- 
 scribed for constant wear in cases of heterophoria. 
 
 Prism Diopter. A prism which has the power to 
 bend a ray of light passing through it and to a 
 distance of one metre beyond, exactly one centi- 
 metre. 
 
 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. 
 
 S^ Prisoptometer (pris-op-tom'-et-er). An instrument 
 used for testing the refraction of the eye by 
 means of a revolving prism. 
 
OPTICAL DICTIONARY. 149 
 
 Probe. A long slender instrument for exploring 
 wounds. Lacrimal p. is a probe designed for use 
 on the tear passages. 
 
 Progressive Myopia. Myopia that is gradually on 
 the increase. 
 
 Prophthalmos (prof-thal'-mos) . A bulging forward 
 or undue prominence of the eyeball. 
 
 Proptosis (prop-to'-sis). A falling down or sink- 
 ing of a part. 
 
 Prothesis Ocularis (pro-the'-sis) . The insertion of 
 an artificial eye. 
 
 Protractor Scale. A device for indicating the 
 location of the axis of a cylinder lens. 
 
 Pseudoglioma (seu'-do-gly-oh'-mah) . A circum- 
 scribed collection of pus in the vitreous. 
 
 Pseudoblepsis (seu-do-blep'-sis). That condition 
 in which objects look different from what they 
 really are. 
 
 Psorophthalmia (soh-rof-thal'-mee-ah). That in- 
 flammatory condition of the eye which is accom- 
 panied with itchy ulcerations. 
 
 Pterygium (ter-yg'-i-um) . A thickening or growth 
 , of the conjunctiva, usually on the nasal side of 
 the eye extending out toward the cornea. It 
 can be removed by operation, and should be as 
 soon as it reaches the cornea; otherwise it will 
 grow over it and impair vision. 
 
 Ptilosis (ti-lo'-sis) . That condition where there is 
 a falling out or loss of the eyelashes. 
 
150 LEWIS POCKET 
 
 Ptosis (to'-sis). A drooping of the upper eyelid. 
 
 V 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 thickening of the upper lid. 
 
 Puncta (punc'-tah). A small prominence or point. 
 (See Puncta Lacrimalia.) 
 
 Puncta Lacrimalia (punc'-ta lak-ri-mal'-i-ah). Two 
 small openings near the nasal end of the sur- 
 face 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 (pu-pil). The central circular opening in the 
 iris. A contracted pupil indicates inflammation 
 of the brain, a sensitive retina, hypermetropia, 
 effect of opium or other drugs. A dilated pupil 
 indicates effect of belladonna or other drugs, 
 myopia, or paralysis of the third nerve. 
 
 Pupillary (pu'-pil-la-ry). Pertaining to the pupil. 
 
 Pupillometer (pu-pil-om'-et-er) . An instrument for 
 measuring the diameter of the pupil. 
 
 Pupilloscopy. (See Retinoscopy.) 
 
 Pupillostatometer (pu-pil-o-stat-om'-et-er) An in- 
 strument to measure the distance between pupils. 
 
 Pyrometer (py-rom'-e-ter). An instrument for 
 measuring high degrees of heat. 
 
OPTICAL DICTIONARY. 151 
 
 Vi^uiz. Instruction by questions and answers. Q. 
 class, a body of students forming a class for the 
 purpose of being questioned by a teacher. (See 
 last few pages.) 
 
 V 
 
 XVadiad (ra'de-ad). 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. 
 
 Tladiant (ra'-de-ant) . Diverging, as rays from a 
 centre. 
 
 Radiation (ra-di-a'-shun) . Where rays of light ap- 
 pear to be thrown off from a common center. 
 
 Radius. 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. 
 
 Range of Vision. The distance between the near 
 and far point. 
 
 Ray. The smallest imaginary line of light. 
 
 Red-Blindness. That condition in which a person 
 is unable to distinguish red. 
 
 Reflection (re-flec'-shun) . Throwing back light. 
 Reflection from a plane surface gives an erect 
 image, 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 
 
152 LEWIS POCKET 
 
 to the distance of the object in front of it, and is 
 called a virtual image. 
 
 Reflection by a concave mirror. Parallel rays 
 falling on a concave surface are reflected as con- 
 vergent rays which meet at a point called the 
 principle focus. 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 vir- 
 tual, erect, and smaller than the object. 
 
 Reflector (re-flec'-tor) . A device for reflecting light. 
 
 Refracting Media. (See Media.) R. System. A 
 lens, or combination of lenses, for the creation of 
 optical images. 
 
 Refraction (re-f rac'-shun) . The bending of a ray 
 "^ of light in passing obliquely from one media to 
 another of different density. Double R., refrac- 
 tion in which the incident ray is divided into 
 two refracted rays. ^ Static R., refraction of the 
 eye at rest.'* Dynamic R., refraction of the eye, 
 plus that secured by accommodation. (See 
 page 153.) 
 
 Refractionist (re-f rac'-tion-ist) . One who is skilled 
 in correcting errors of refraction of the eye. 
 
 Refractive (re-frac'-tive). Pertaining to refraction. 
 
 Refractometer (re-f rac-tom'-e-ter) . An instrument 
 for measuring refraction. 
 
 Regular (reg'-u-lar) . According to rule; normal. 
 
OPTICAL DICTIONARY. 
 
 153 
 
 Relative Index of Refraction is that which is found 
 when light passes from atmospheric air into 
 another medium. 
 
 Relaxa'tion. A lessening of tension. 
 
 Remedy. Anything acting as a cure for, or the 
 relief from, unhealthy conditions. 
 
 Ai it emtr^t$ 
 REFRACTION BY PLANE SURFACE. 
 
 No. 1 ray oi light is called the incident before entering the 
 second medium. A ray passing from a rarer to 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 medium, 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 
 inciclent 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 Ul 
 the reflected ray, and A at F. 
 
154 LEWIS POCKET 
 
 Reposition (re-po-zi'-shun). The act of putting 
 back in a normal position. 
 
 Retina (ret'-in-a). 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 protective or containing 
 membranes. The retina is the immediate con- 
 tinuation of the optic nerve, which extends from 
 the brain to the eyeball, perforates the sclerotic 
 
 CL— MMCHIL-A LX/TIM, THE- nO&T 
 SenSITIVB PARTOF-TMEr RfcTl/iM. 
 
 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 the cut under anatomy. 
 The functions of the retina are to receive the 
 pictures which are formed within the eye by 
 means of the waves of light reflected from objects, 
 
V 
 
 OPTICAL DICTIONAll/. 155 
 
 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 degree 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 sensi- 
 tiveness gradually diminishes to its most anterior 
 edge. The retina does not extend as far forward 
 as the choroid, but terminates 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 ora serrata. 
 
 Structures of the Retina according to 
 Gray. — From within outwards the layers of the 
 retina are named as follows : 
 
 Membrana limitans interna. 
 
 Fibrous layer, consisting of nerve fi- 
 
 Vesicular layer, consisting of nerve 
 
 Inner molecular, or granular layer. 
 Inner nuclear layer. 
 Outer molecular, or granular layer. 
 Outer nuclear layer. 
 Membrana limitans externa. 
 Layer of rods and cones, or Jacob's 
 Membrane. 
 
 No. 10. Pigmentary layer. 
 
 No. 
 
 1. 
 
 No. 
 
 2. 
 
 bers. 
 
 
 No. 
 
 3. 
 
 cells. 
 
 
 No. 
 
 4. 
 
 No. 
 
 5. 
 
 No. 
 
 6. 
 
 Noo 
 
 7. 
 
 No. 
 
 8. 
 
 No. 
 
 9. 
 
\^ 
 
 156 ' LEWIS POCKET 
 
 Retinal Reflex, A term used in retinoscopy to 
 designate the light reflected from the retina and 
 creating the Hght in the pupil. 
 
 Retinitis (ret-in-i'-tis) . 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 reduced 
 both because of the changes in the retina itself 
 and because of the accompanying opacities 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 perfectly 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, recurrent 
 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. 
 
OPTICAL DICTIONARY. 157 
 
 Retinoscope (ret'-in-o-scope). An instrument 
 with which an objective examination of the diop- 
 tric state or condition of the eyes may be meas- 
 ured. (Made in plane and concave.) 
 
 The plane is used for retinoscopy only, while 
 the concave can be combined with a strong plus 
 lens, about 20-D., and used as an ophthalmo- 
 scope. 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 reverse; the 
 shadow in hypermetropia, emmetropia, and a 
 small amount of myopia will go against the mirror. 
 In more than ,75 of myopia, the movement will 
 be with the mirror. 
 
;5S LEWIS POCKET 
 
 It makes no difference which you use, the find- 
 ings will be the same, and you deduct from plus 
 and add to minus findings the same amounts; it 
 depends on the distance you are sitting from the 
 patient. When sitting at a little over 40 inches 
 you subtract one diopter from all plus findings, 
 and add — .75 to all minus findings. When work- 
 ing between 53 and 60 inches you subtract .75 
 from all plus findings and add — .50 to all minus 
 findings. 
 
 Retinoscopy (ret-in-os'-co-py) . Hetinoscopy, or the 
 Shadow Test, is one of the best and most popular 
 methods of estimating 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. 
 
 Retinoscopy 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. The 
 first case: 
 
 Hypermetropia. — Taking my seat between 53 
 and 60 inches from the patient, holding the mirror 
 in my right hand before my right eye, I look 
 through the small hole in its center at the pupil 
 of the patient's eye, at the same time reflecting 
 the light from the lamp to the patient's face. 
 The light must not be too strong, but just strong 
 enough to illuminate the eye of the patient. When 
 
OPTICAL DICTIONARY. 159 
 
 you are examining the right eye, have the patient 
 look slightly over your right shoulder, and if the 
 left eye, have him look over your left shoulder. As 
 a result of this arrangement the pupil of the eye 
 under observation is illuminated, and has a reddish 
 color. It is really the illuminated spot on the 
 retina seen through the dioptric media, and is 
 called the fundus reflex, taking its color from the 
 blood-vessels of the retina. The dark non- 
 illuminated areas surrounding it are what are 
 known as the shadows. 
 
 Now, if we tilt the mirror from right to left, 
 we will notice the shadow in the pupil move from 
 left to right, and is said to go against the mirror; 
 now we place in the trial frame on the patient's 
 face a plus .50 sphere, and if this does not reverse 
 the shadow, increase its strength until we find 
 the weakest plus sphere that will just reverse its 
 movements; we will say in this case it was + 2.50. 
 As we are examining the horizontal meridian we 
 write +2.50 on the horizontal arm of the cross. 
 We now remove the lens and rotate the mirror, 
 working up and down the vertical meridian. The 
 shadow will move against as before, and if there 
 is no astigmatism will require the same amount 
 of plus to reverse it, so we write +2.50 on the 
 vertical arm of the cross. 
 
 The examination of this eye being finished, we 
 then make another cro ;s, being careful not to 
 change the meridians, and subtract +.75 from 
 each arm, and write the amount remaining on 
 the same arms, but on the new cross; this will 
 be +1.75. From this cross we write the prescrip- 
 tic n, and having the same power in all meridians, 
 the prescription will be +1.75 sphere. 
 
160 ' LEWIS POCKET 
 
 Myopia. — Taking your position as in the pre- 
 vious case, rotate your mirror as before, and if 
 there is less than .75-D of myopia the shadow will 
 move against, and would require plus to reverse 
 it in each meridian. We will say that in this 
 case it required + . 50 to reverse the shadow in 
 both meridians. As we subtract +.75 from all 
 plus findings this will leave us — .25 in all meri- 
 dians, which should be the correction for this case. 
 
 Should there be .75-D or more, the shadow will 
 move with the concave mirror, and must be re- 
 versed with the weakest minus lens in each 
 meridian. In this case it required — 1.50 to re- 
 verse the shadow in the horizontal meridian, and 
 the same amount for the vertical. Then we 
 make a cross as before and add — .50 to each arm. 
 This would make it — 2 in all, and the prescrip- 
 tion would be — 2 sphere. 
 
 Astigmatism. — Is a difference of refraction of 
 the meridians of an eye, one meridian of the eye 
 possessing a greater dioptric value than the one 
 at right angles to it. It is evident that in exam- 
 ining such an eye with the retinoscope, the ob- 
 serving eye cannot watch both meridians at the 
 same time. Whenever there is astigmatism the 
 shadow will move faster in one meridian, and the 
 reflex will have a band-like or straight edge. If 
 this bright band is seen straight up and down in 
 the vertical meridian, it will move faster across 
 the horizontal meridian, and if the shadow moves 
 against the mirror, we will use a plus cylinder, 
 placing the axis parallel with the bright band; 
 in this case it would be the 90th meridian. Had 
 the shadow moved with the mirror, we would 
 have used a minus cylinder; but in either case 
 
OPTICAL DICTIONARY: 
 
 161 
 
 increase the strength of the cyhnder until j^ou 
 find the weakest that will just reverse the move- 
 ment of the shadow. Then leaving this cylinder 
 in its position, work through its axis and reverse 
 the shadow in this meridian with another cylinder, 
 placing the axis at right angles to the one already 
 in the trial frame, which would be the 180th 
 meridian in this case. Now, as you have just 
 reversed the 2d meridian, make a cross on your 
 paper, having its meridians correspond to those 
 examined in the eye, and on each arm write the 
 
 ^1. 
 
 1^* -f-5^.- 
 
 90* 
 
 1800 
 
 90 
 
 power it required to just reverse the shadow. 
 In doing this take no notice of the axis of your 
 cylinder. The cross you have already made is 
 known as the retinoscopic findings, so you must 
 make another cross as before and subtract .75 
 from all plus findings, and to minus findings 
 add — .50, and the remainder write on the arm? 
 of the new cross, being careful not to change the 
 meridians. From this cross you write ^ )\jr 
 prescription. We will say in this case that the 
 retinoscopic finding was +2 in the vertical, or 
 90th meridian, and + 1 in the horizontal merid- 
 iaUt Now, as we have to subtract ,75 from all 
 
162 
 
 LEWIS POCKET 
 
 plus findings it will leave us +1.25 in the ver- 
 tical meridian and +.25 in the horizontal 
 meridian of the prescription cross. From these 
 findings, we write the prescription without 
 changing the optical value of the cross. 
 
 The prescription in this case would be 
 + 1 . 25 sph. O — 1. cyl. ax. 90. 
 or + .25 sph. O +1. cyl. ax. 180. 
 
 The cylinder always represents the amount of 
 astigmatism in the eye. The following are a 
 few cases as examples: 
 
 ■7t50- 
 
 i8o^ 
 
 90** 
 
 Prescription — 
 
 — 1. sph. 
 or — .25 'sph. 
 
 -25- 
 
 fSO'' 
 
 BO'' 
 
 + . 75 cyl. ax. 90. 
 — .75 cyl. ax. 180. 
 
 -^. 
 
 .5.50 
 
 -^50 
 
 Prescription — 
 
 —3.50 sph. 
 or — 2.50 sph. 
 
 ^S' 
 
 + 1 cyl. ax. 135. 
 — 1 cyl. ax. 45. 
 
 /35« 
 
OPTICAL DICTIONARY. 163 
 
 Retractor (re-trac'-tor) . An instrument used for 
 drawing and holding the parts away while under- 
 going an operation, or for any other purpose. 
 
 Retrobulbar (re-tro-bul'-bar) . That which is situ- 
 ated or occurring behind the eyeball. 
 
 Reversal Point. (See Point of Reversal.) 
 
 Rheum (rume) . A watery discharge from the eyes. 
 
 Rhodopsin (ro-dop'-sin). Visual purple; pigment 
 of outer segment of retinal rods. 
 
 Rhytidosis (rit-id-o'-sis) . A wrinkling, as of the 
 cornea. 
 
 Rod. Relates to the 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). 
 
 Romberg's Symptoms. Difficulty in standing when 
 the eyes are shut: a sign of locomotor ataxia. 
 
 Rota'tion. 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. 
 
164 LEWIS POCKET 
 
 5^ac. A bag-like organ. 
 
 Saemisch's Ulcer (sa'-mish-ez) . Infectious corneal 
 ulcer. 
 
 Sarcoma (sar-ko'-mah) . A tumor made up of a 
 substance like the embryonic connective tissue. 
 It is often highly 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 con- 
 cealed from view by the iris. Occasionally it 
 makes its first appearance at the angle of the 
 anterior chamber. 
 
 Schematic Eye (ske-mat'-ik) . A model or diagram 
 of the eye. 
 
 Schlemm's Canal. A lymph channel in the first 
 tunic, between the cornea and the sclerotic. 
 (See Anatomy.) 
 
 Scintillation (pcin-til-la'-shun). A sensation of 
 sparks before the eye. 
 
 V Scissors Movement. A peculiar movement of the 
 retinal reflex, resembling the opening and shut- 
 ting of a pair of scissors. It indicates a condition 
 of irregular astigmatism. 
 
 Sclera (skle'-ra). The external coat of the eyeball, 
 or sclerotic. 
 
 Scleral. Pertaining to the sclera. 
 
 Sclerectasia (skle-rec-ta'-si-ah). A bulging state of 
 the sclera. 
 
OPTICAL DICTIONARY. 166 
 
 Sclerectomy (skle-rek'-to-my) . Excision of a por- 
 tion of the sclera. 
 
 Sclerectasis (skle-rek'-ta-sis). A protrusion of the 
 sclerotic coat. (See Staphyloma.) 
 
 Scleriritomy (skle-rir-if-o-my). Incision of the 
 sclera and iris'in anterior staphyloma. 
 
 Scleritis (skle-ri'-tis) . Inflammation of the sclerotic 
 coat. 
 
 Sclerochoroiditis (skle-ro-cho-roid-i'-tis) . Inflam- 
 mation of both the choroid and the sclerotic coats 
 of the eye. 
 
 Scleroconjunctival (skle-ro-con-junc-ti'-val). That 
 condition in which the sclera and the conjunctiva 
 are concerned. 
 
 Sclerocorneal Sulsus (furrow). 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. 
 
 Scleroiritis (skle-ro-i-ri'-tis) . An inflammation 
 which involves both the iris and sclera. 
 
 Sclerokeratoiri'tis. Inflammation of the sclera, cor- 
 nea, and iris. 
 
 Scleronyxis (skle-ro-nyx'-is) . A perforation of the 
 sclerotic coat. 
 
166 LEWIS POCKET 
 
 Sclerophthaimia (skle-rof-thal'-mi-ah) . That condi- 
 tion in which the sclera overlaps the cornea, so 
 that only a portion of the latter remains clear. 
 
 Scle'rosed. That condition in which a part is 
 affected with sclerosis;, a hardening. 
 
 Sclerotic (skle-rot'-ic) . 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 in- 
 terior, and at the same time acts as a dark-box 
 or camera. It is to this coat that the muscles are 
 attached. The sclerotic is thickest in the pos- 
 terior part, where it has a thickness of about one 
 millimetre. It gradually diminishes in thickness 
 toward the anterior part, becoming somewhat 
 thicker near the cornea, 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. 
 
 Scleroticectomy (skle-rot-i-kek'-to-my) . An opera- 
 tion for cutting through any part of the sclerotic. 
 
 Scotodinia (sko-to-din'-iah) . Dizziness, with head- 
 ache and dimness of vision. 
 
 Scotoma (sko-to'-mah) . That condition in which 
 V there is a blind or partially blind area in the 
 visual field. Sometimes the patient will com- 
 plain of seeing dark, vanishing cloudy spots be- 
 fore the eyes. Absolute s., a part of the visual 
 field in which there is absolute blindness. 
 
OPTICAL DICTIONARY 167 
 
 Scotometer (sko-tom'-e-ter, . An instrument for 
 measuring scotoma. 
 
 Seborrhea (seb-or-e'-ah) . An abnormal secre cion 
 of the sebaceous glands. 
 
 Seg'ment. A section of a circle. A cylindrical lens 
 is a segment 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). Resembling a ring- 
 worm. 
 
 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 de- 
 scribed, 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 spherical 
 and convex cylindrical lenses. The sign of sub- 
 traction ( — ) is used to represent concave spheri- 
 cal and concave cylindrical lenses. 
 
 Sine. (A bent surface, curve). Length of a per- 
 pendicular drawn from one extremity of an arc to 
 the diameter drawn through the other extremity; 
 the perpendicular itself. 
 
168 
 
 LEWIS POCKET 
 
 Sinis'trad. To or toward the left. 
 
 Skiascope (ski'-as-kope) . Better known as the retin* 
 oscope. 
 
 Skiascopy. (See Retin^scopy.) 
 
 E 
 
 c 
 
 B 
 
 D L N 
 
 P T 
 
 E R 
 
 r z 
 
 B D E 
 
 or L 
 
 . C T G 
 
 »"'" 
 
 Z.OTHKC 
 
 Snellen Chart. 
 
 Snellen, M. D., Prof. H. Born in Holland. A pro- 
 fessor of ophthalmology occupying the chair 
 at the University at Utrecht, Holland. A pupi]. 
 of Dr. F. C. Bonders, whom he succeeded in 
 practice 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 
 determined. It is held by Snellen that in order 
 to distinguish one letter from another the eye 
 must be able to distinguish the spaces between 
 
OPTICAL DICTIONARY. 169 
 
 the lines which correspond to a visual angle of 
 1'. This is true for certain letters, as, for in- 
 stance, to differentiate between O and C, where 
 the eye must distinguish the white space 
 which interrupts 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 acuteness and the refraction at the same 
 time. We must determine the refraction at such a 
 distance 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-blindness. 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). A hollow part into which a cor- 
 responding part fits. 
 
 Spasm. An involuntary contraction of a muscle. 
 Spasm of accommodation is a spasmodic con- 
 traction of the ciliary muscles, thus increasing the 
 
J70 LEWIS POCKET 
 
 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 
 relax intermittently. 
 
 Spectacles. A pair of lenses mounted in frames with 
 temples attached. 
 
 Spectrum (spec'-trum) . The analysis of the seven 
 colors which after passing through a prism be- 
 come separated. * 
 
 Sphere. A lens with the same power in all meri- 
 dians. 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) . That which resembles a 
 sphere in shape. 
 
 Spherometer. An apparatus for measuring the cur- 
 vature of a surface. 
 
 Sphincter (sphinc'-ter) . A ring-like muscle. The 
 sphincter muscle of the iris when contracted 
 closes down the pupil. When relaxed, allows the 
 pupil to become dilated. 
 
 Spintherism (spin'-ther-ism). That condition in 
 which the patient complains of seeing star-like 
 flashes of light. 
 
OPTICAL DICTIONARY. 171 
 
 Squint. Cross Eyes. Strabismus. A condition in 
 which there is a deviation of the visual axis of 
 one of the eyes from the correct positon of fix- 
 ation when looking at a point. The deviation 
 may occur in any direction. (See Concomitant 
 Strabismus.) 
 
 Staphyloma (sta-fy-lo'-mah). A bulging of the cor- 
 nea or sclera. Anterior s., a bulging forward of 
 the anterior portion of the eye. Posterior s., 
 backward bulging of the posterior pole of the eye. 
 
 Stat'ic. Not in motion; in a state of rest. The 
 static refraction is the refraction of the eye 
 with the muscles ' of accommodation at rest; 
 just the reverse to dynamic refraction. 
 
 Steato'sis. That condition in which we have fatty 
 degeneration; disease of the sebaceous glands. 
 
 Stenopaic Slit (sten-o-pa'-ic slit). 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 
 by some refractionists for the purpose of finding 
 the two principal meridians in cases of astigma- 
 tism. The disc is placed in the trial frame in 
 front of the eye we are about to examine. The 
 patient is requested to look steadily at the dis- 
 tant chart. The disc is then slowly rotated until 
 a complete circle of the eye is made, after which 
 it is always best to allow the patient to rotate 
 it for himself, and to stop when the best vision 
 is obtained. This would be considered one of 
 the principal meridians. We then try convex 
 spheres in front of the slit. If this meridian 
 should show hypermetropia we continue to in- 
 
172 LEWIS POCKET 
 
 crease the plus until we find the strongest that 
 will allow the best vision. We then take note 
 of the number or meridian on the trial frame, and 
 make a cross on a piece of paper at the same angle 
 as the slit was placed in the frame, and write on 
 the arm of each, the power of the lens required 
 for correction. So far we have only tested one 
 meridian. We now rotate the slit 90 degrees and 
 
 correct this meridian as before, writing down the 
 power of the lens used on the second arm of the 
 cross. Now from this cross we write the pre- 
 scription without adding or subtracting, as we 
 do in cases of retinoscopy. 
 
 Stereoscope (ster'-e-o-scope). An instrument com- 
 posed 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 out. 
 
OPTICAL DICTIONARY 173 
 
 Stereoscopic Vision (ster-e-p-scopMr). Where we 
 have equal vision with the two eyes and the ob- 
 jects appear to stand out in soHd form, and are 
 not seen as flat pictures. 
 
 Stilling's Canal. A small canal leading from the 
 \^ optic disc through the vitreous humor to the lens 
 of the eye. (See Anatomy.) 
 
 Stillicidium (stil-li-sid'-i-um). An overflowing of 
 the tears upon the cheek due to a stricture of or 
 a narrowing of the nasal duct. (Same, as epiphora.) 
 
 Stilus (sti'-lus). A small instrument made of gold 
 or silver used for dilating the lacrimal duct. 
 
 Stoke's Lenses. An instrument that was used in 
 the diagnosis of astigmatism.' 
 
 Stop-needle. A needle with a disc attached 
 to regulate the depth of penetration. 
 
 Strabismometer (strab-is-mom'-e-ter) . An instru- 
 ment for measuring the degrees of strabismus. 
 
 Strabismus (stra-bis'-mus). That condition in 
 y which the eyes turn away from parallelism. This 
 condition can be seen by an observer. The cause 
 of strabismus may be due to an uncorrected error 
 of refraction, for when a person has an error 
 of refraction in one eye that interferes with the 
 vision of its fellow, he will ^earn to turn the eye 
 with the error to one side.\j Concomitant s. is 
 that form of strabismus in which one eye, although 
 deviated, always moves with the other, so that 
 the amount of deflection remains the same. 
 Paralytic s. is due to paralysis of one or more of 
 the extrinsic muscles, and the eye remains sta- 
 
 \ 
 
174 
 
 LEWIS POCKET 
 
 tionary. 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 nerve. 
 
 One Eye turning in. 
 
 Both Eyes turning in. 
 
 Both Eyes turning out. 
 
 When the eye attempts to accommodate in order to 
 overcome the hypermetropia, the internal rectus 
 will contract, and if the patient has not the nerve 
 energy to control the external rectus, the eye will 
 turn in. 
 
OPTICAL DICTIONARY. 175 
 
 Strabotomy (stra-bot'-o-my). An operation calling 
 for the cutting of an ocular tendon for relief in 
 cases of strabismus. 
 
 Strain. Injury from over-use. 
 
 Stye. Inflammation of a sebaceous gland of the 
 eyelid. It lies near the border of the lid, and 
 corresponds to the inflamed gland. In a day or 
 two the swelling at this spot increases, and the 
 skin over it grows red, afterward shows a yellow- 
 ish discoloration, and finally is perforated near 
 the border of the lids, with a discharge of pus. 
 After the evacuation of the pus the inflammatory 
 . symptoms rapidly abate, the small abscess- 
 cavity soon closes, and the entire process comes 
 to an end. Eye-strain is a common cause. 
 
 Subarach'noid Space. 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 percept- 
 ible to any other person. It refers to the patient 
 as he sees objects or feels concerning his own im- 
 pressions. 
 
 Subla'tio Ret'inae. Detachment of the retina. 
 
 Subluxa'tion. 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 
 
176 LEWIS POCKET 
 
 anterior chamber. In cases of luxation, that is, 
 where the lens has left its place in 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 con- 
 siderable disturbance of vision. If the lens still I 
 lies behind the pupil the eye becomes very myopic, 
 because the lens is allowed to assume its maxi- 
 mum convexity on account of separating frOm 
 the' suspensory ligaments which keep it elongatedft 
 when the eye is at rest. Invariably any tear in' 
 the suspensory ligament results in soft cataract. 
 Added to this is a considerable degree of astig- 
 matism. Dislocations of the lens usually entail I 
 secondary consequences which may be ex- 
 tremely disastrous to the eye, but in those 
 cases in which the dislocation entails no further 
 injurious consequences than the disturbance of 
 vision, the treatment consists in prescribing 
 suitable glasses. 
 
 Suborbital (sub-or'-bit-al) . Beneath the orbit. 
 
 Subretinal (sub-ret'-in-al). Situated beneath the 
 retina. 
 
 Subvolution (sub-vo-lu'-shun) . An operation for 
 the removal of a pterygium. 
 
 Suction (suc'-shun). A method by which fluid is 
 withdrawn. 
 
 Suffusion (suf-fu'-zhun). State of being blood-shot, 
 or of being moistened. A suffusion of tears is an' 
 excess of the flow of tears, 
 
 Super Cilia. (Upper hairs.) The eyebrows. 
 
OPTICAL DICTIONARY. 177 
 
 Superciliary (sii-per-cil'-i-a-ry) . That which per< 
 tains to the eyebrow. 
 
 Supra Choroidal Space. The space between the 
 sclerotic and choroid. 
 
 Supraduction, Sursumvergence. The power of the 
 superior rectus muscles. 
 
 Supraorbital (su-pra-or'-bi-tal) . Located over the 
 
 orbits. 
 
 Sursumduction (sur-sum-duk'-shun). The act of 
 turning one eye up and the other down. The 
 test is made by placing the base of prisms up or 
 down until we find the strongest with which the 
 eye can see an object singly. 
 
 Sursumvergens (sur-sum-vur'-jenz). A tending up- 
 ward, as in vertical squint. 
 
 Suspensory (sus-pen'-so-ry). 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 cDiary 
 body, divides and forms the suspensory ligaments, 
 which are attached to the lens capsule. C. B. 
 Lock wood, in a journal of Anatomy and Physi- 
 ology, vol. XX., part I. — Ed. of 15th English 
 edition, has also described a thickening 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 centre and narrow at its ex- 
 tremities, which are attached to the malar and 
 lachrymal bones respectively. 
 
V 
 
 178 LEWIS POCKET 
 
 Symblepharon (sym-blef '-ar-on) . 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 consequence be- 
 come adherent. Causes which can give rise to 
 the formation of raw surfaces upon the conjunc- 
 tiva are burns by the action of heat, burns from 
 caustic substances, diphtheria, operations, ulcers 
 of all kinds, etc. 
 
 Sympathetic Ophthalmitis (sym-pa-thet'-ik of-thal- 
 mi'-tis). An inflammatory condition of the iris 
 and ciliary body, which is developed through an 
 injury or disease of the opposite eye. 
 
 Symptoms. A perceptible change which indicates 
 disease, or that which indicates the existence of 
 something else. (See Objective and Subjective 
 Symptoms.) 
 
 Synchysis (syn'-chy-sis) . Liquefaction of the vitre- 
 ous. When observing opacities 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. That condition in which there is in- 
 flammation of a ligament or of the conjunctiva. 
 
 Synechia (syn-e'-chi-'^h),. Adhesion, as of the iris to 
 the lens or cornea. yPMerior s., adhesions of the 
 iris to the lens capsule. \ Anterior s., adhesions of 
 the iris to the cornea. 
 
OPTICAL DICTIONARY. 179 
 
 Synizesis (sin-iz-e'-sis). Contraction of the pupil of 
 the eye. 
 
 Synophthalmus (syn-of-thal'-mus) . A one-eyed 
 monster. 
 
 Syntropic (sin-trop'-ik) . Turned in the same direc- 
 tion. 
 
 System. The bodily organism. An assemblage of 
 parts or organs which unite in a common function. 
 
 T» -A.n abbreviation for tension or temperature. 
 
 Tapetum (ta-pe'-tum) , The luminosity seen in the 
 eyes of many beasts. A lustrous, greenish mem- 
 brane seen in the eyes of cats. 
 
 Tarsal Cartilages (tar'-sal kar'-til-aj-es). The cartil- 
 ages that give the eyelid its shape. 
 
 Tarsitis (tars-i'-tis) . An inflammation involving the 
 tarsal cartilages. 
 
 Tarsoplasty (tar'-so-plas-ty) . Plastic surgery of the 
 tarsus. 
 
 Tarsorrhaphy (tar-sor'-a-f e) . An operation upon 
 the eyelids. 
 
 Tarsotomy (tar-sot'-o-my). A surgical operation 
 which involves the cutting of the tarsal cartilages. 
 
 Tarsus (tar'-sus). That which forms the skeleton 
 of the eyelid, giving it rigidity of form and afford- 
 ing it firm support. The tarsus of the upper lid 
 is broader than that of the lower. 
 
180 LEWIS POCKET 
 
 Tears. The watery secretion of the lacrimal glands. 
 
 Teichopsia (tei-kop'-si-ah). A luminous appearance 
 before the eyes, with a zigzag, wall-like outline. 
 
 Telangiectasis (tel-an-je-ek'-ta-sis). Dilatation of 
 capillaries. 
 
 Tendency (tend'-en-cy). A disposition on the part 
 of a muscle to incline toward certain directions. 
 
 Tendon (ten'-don). The fibrous cords by which the 
 muscles are attached. 
 
 Tenonitis (ten-on-i'-tis). Inflammation of the Cap 
 sule of Tenon. 
 
 \ Tenon's Capsule. The capsular non-bony socket of 
 V the eye. This extends forward as far as the con- 
 junctiva of the eyeball and backward nearly to 
 the optic nerve. It is thus open in front and be- 
 hind, and may be said to represent a broad ring 
 placed about the eyeball. It forms the articular 
 socket for the eyeball, which can move in it 
 freely in all directions. (See Anatoitiy.) 
 
 Tenotomy (ten-ot'-om-e) . An operation for cutting 
 or dividing the tendon of a muscle. 
 
 Tension (ten'-shun). 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 sac. 
 
OPTICAL DICTIONARY. 181 
 
 Test. An examination or trial. T. type§, letters of 
 various shapes and sizes used in testing visual 
 power. 
 
 Tetranopsia (tet-ran-op'-si-a) . Obliteration of one- 
 fourth of the visual field. 
 
 Thermometer (ther-mom'-e-ter) . An instrument 
 for ascertaining temperatures. 
 
 Thrombosis (throm-bo'-sis) . The formation of a 
 blood-clot in a vessel at the point of obstructioi . 
 
 Thyroid (thi'-roid). Shield-shaped. T. Gland is 
 a vascular body situated at the front and side s 
 of the neck, and extending upwards upon er ( h 
 
 ' side of the larynx. It is a single gland, varying 
 greatly in size in different individuals. 
 
 Tinea Tarsi. Blepharitis marginalis. (See Bleph- 
 aritis.) 
 
 Tobacco Amaurosis. 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 alraost always the same in both 
 eyes. Treatment consists, first of all, in absti- 
 nence from tobacco, and it is probable that in 
 light cases this alone is suiiicient to effect a cure. 
 
 ^ Tonic Spasm. A continuous involuntary contrac- 
 y tion of the ciliary muscles. This condition may 
 exist in any muscle. 
 
 \ 
 
 Tonometer (to-nom'-e-ter) . An instrument for 
 measuring the tension of the eyeball. 
 
 Toric IJens. A lens with a sphere and a cylinder on 
 the same side) periscopic in shape. (See page 225) 
 
V 
 
 182 LEWIS POCKET 
 
 Torsion (tor'-shun). A twisting. 
 
 Toxic Amblyopia. Amblyopia caused by a poison, 
 a common cause being excessive use of tobacco 
 or liquor or both. 
 
 Trachoma (tra-ko'-mah) . Granular conjunctivitis. 
 Characterized by slowly progressive changes in 
 the conjunctiva of the eyelids, in consequence of 
 which this membrane becomes thickened, vascu- 
 lar, and roughened by firm round elevations, in- 
 stead of being pale, thin, and smooth. Granular 
 disease is very important, because it greatly in- 
 creases the susceptibility of the conjunctiva to 
 take on acute inflammation and to produce con- 
 tagious discharge. It often gives rise to deformi- 
 ties of the lid and to serious damage of the cornea. 
 The conditions which favor the development and 
 spread of trachoma are unclean and overcrowded 
 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) . A section made across 
 a long axis. 
 
 Transillumination (trans-il-lu-min-a'-shun). The in- 
 spection of the interior of an organ by means of a 
 strong light. 
 
 Transit. A passing across. A term used in re- 
 tinoscopy to indicate movement of the light 
 area. 
 
 Transi'tional Zone. The posterior part of the lens 
 sac during the stage of growth. 
 
OPTICAL DICTIONARY. 183 
 
 Translu'cent. The quality of transmitting rays of 
 light without the object being distinctly seen. 
 (Frosted Glass,) 
 
 Transparent. Having the property of being clearly 
 seen through. 
 
 Transposition (trans-po-si'-shun). Changing the 
 form of an optical prescription without changing 
 its optical value. In order that you may be en- 
 abled to give your patients glasses which give 
 them the best possible vision, it is necessary for 
 you to know how to build lenses which produce a 
 periscopic effect; this periscopic effect being the 
 prime and important feature in every instance 
 The term periscopic is applied to spectacles having 
 concavo-convex lenses, which enable the eye to 
 view with equal likeness on all sides. When 
 lenses are not of this description the desired re- 
 sult 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 to- 
 gether for the new sphere, prefixing the same sign. 
 
 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 ol . 
 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 angl ; (i. e., 
 move it 90 degrees). 
 
 For transposition of simple cylinders, use the 
 following 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 
 
184 LEWIS POCKET 
 
 as the original, but prefix the opposite sign and 
 change the axis to right angle. 
 
 To convert cross cylinders into sphero-cylinders. 
 apply the following 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 answers: (See page 215.) 
 
 Example, + 3 sph. O — 2 cyl. ax. 60. 
 Answer, -f- 1 sph. O +2 cyl. ax. 150. 
 Example, +2 sph. o +2 cyl. ax. 90. 
 Answer, +4 sph. o — 2 cyl. ax. 180. 
 Example, +4 cyl. ax. 45 o +2 C3^^ ax. 135. 
 Answer, + 2 sph. Q + 2 cyl. ax. 4o. 
 Example^ — 3 cyl. ax. 20 o +3 cyl. ax. 110. 
 Answer, — 3 sph. o +6 cyl. ax. 110. 
 Example, + 1 cyl. ax. 60. 
 Answer, + 1 sph. o — 1 cyl. ax. 150. 
 
 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, 
 
OPTICAL DICTIONARY. 185 
 
 ranging from 0.1 2-D. up to 20-Diopters; twenty- 
 pairs of convex and the same number of con- 
 cave cylindrical lenses ranging from 0.1 2-D, up 
 to 6-D.; at least ten prisms from 1 to 10 
 degrees; a plain red tinted glass; some shades 
 of smoked glasses; an opaque disc; stenopaic 
 slit; pinhole disc; a ground glass disc; a Maddox 
 rod, or double prism, and a retinoscope; two trial 
 frames, one having three cells to be used in 
 
 Trial Case. 
 
 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 
 
186 LEWIS POCKET 
 
 the patient'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 find 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 you take a plus sphere from the trial case, 
 say plus .50-D., place it before the right eye, ask- 
 ing 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 emme- 
 tropia, myopia, or astigmatism; 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 proceed to work out a case of each kind. 
 Hypermetropia. — Place the trial frame on the 
 patient's face, cover the left eye with the opaque 
 > disc, and ask the patient which is the smallest 
 line he can read correctly. 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 .50 sphere, and if the patient reads the 
 same or a line better, it is surely a case of hyper- 
 metropia. Now, as a plus will always relax ac- 
 commodation, and we do not want any eye to 
 accommodate for 20 feet, or farther, we will add 
 
OPTICAL DICTIONARY 187 
 
 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 uncovered; 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 the best 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 wheel, asking 
 him,'' are all the spokes in the wheel equally clear 
 and of the same density?" If there is no astig- 
 matism 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 correction. 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 th?> 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 accommo- 
 dating before we correct the astigmatism, we will 
 increase the plus sphere (already 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 
 
188 LEWIS POCKET 
 
 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 cylin- 
 der. 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, increase 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 ci:iart, and 
 gradually reduce the strength of your plus 
 sphere while it improves the distant visioft. In 
 other words, the strongest 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 astigmatic wheel and 
 say," can you see the spokes in the wheel, and do 
 
OPTICAL DICTIONARY. 189 
 
 they look equally clear?'' If he cannot see any of 
 the spokes clearly enough to count the lines, re- 
 move a quarter D. of the plus sphere. If with 
 this he fail 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 weak- 
 est 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, we 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 required a minus .75 cylinder, that 
 cylinder combined with the sphere already in the 
 frame will be the correction, which will read as 
 follows: — 1.25 sph. O — .75 cyl. ax. 180. 
 
 Trichiasis (trick-i'-a-sis). That condition where the 
 / eyelashes, instead of extending forward, are di- 
 rected more or less backward, so as to come in 
 
190 LEWIS POCKET 
 
 contact with the cornea. Trichiasis causes a con- 
 tinual irritation of the eyeball, due to the action 
 of the cilia (eyelashes); there is photophobia, 
 lachrymation, and a constant sense of a foreign 
 body in the eye. The cornea itself suffers consid- 
 erable injury. 
 
 Trichitis (trick-i'-tis) . Inflammation of the root of 
 the eyelashes. 
 
 Trichosis (tri-ko'-sis). A disease of the hair. (See 
 Trichiasis.) 
 
 Trichroic (tri-kro'-ik) . That which exhibits three 
 different colors in three- different positions. 
 
 Trichromatic (tri-kro-mat'-ik) . That which has 
 three colors. 
 
 Triplet. A combination of three lenses. 
 
 Triplopia (trip-lo'-pi-ah) . That condition in which 
 there are three images of the same object formed 
 upon the retina. 
 
 \ Trochlea (troch'-le-ah) . A pulley-shaped part, such 
 ^ as that through which the superior oblique mus- 
 cle passes. 
 
 Trochlearis (troch-le-a'-ris). That which refers to 
 the superior oblique muscle. 
 
 Tumor (tu'-mor). A swelling. A growth of new 
 tissue, differing in structure from the part on 
 which it grows, not the result of inflammation. 
 
 Tunic. Coat or covering. The eye has three tunics; 
 from without inward they are: first, sclerotic and 
 cornea; second, choroid, ciliary body, and iris; 
 third, the retina.. 
 
OPTICAL DICTIONARY. 191 
 
 Tunica. Same as tunic. T. adnata, that portion of 
 the conjunctiva which comes in contact with the 
 eyeball. 
 
 Tiitam'ina Oculi. The protecting appendages of 
 the eye, such as the eyelids and lashes. 
 
 Typhlorogy. A treatise on blindness. 
 
 Typlilo'sis. Blindness. 
 
 Tylosis (ty-lo'-sis). A thickened, ulcerated condi- 
 tion of the lid margins after ulceration. 
 
 U leer. An open sore, other than a wound. 
 
 Ulceration (ul-ser-a'-shun) . Formation of an ulcer. 
 
 Umbo (um'-bo). 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 spheri- 
 cal lens. 
 
 Umbra. A shadow. 
 
 Undula'tion. A wave-like motion 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) . That which has but one 
 
 axis. 
 
 Unioc'ular. Only one eye. 
 
 Uremia (u-re'-me-ah). Blood-poisoning from re- 
 tained urinary excretions. 
 
192 LEWIS POCKET 
 
 UTaef ormis (u-ve-f or'-mis) . The middle coat of the 
 choroid. » 
 
 Uvea. The choroid, ciHary body, and iris together. 
 
 Uveal Coat. The second tunic or coat of the eye- 
 ball. 
 
 Uveitis (u-ve-i'-tis) . That condition in which the 
 uvea is inflamed. Iritis. 
 
 Uveal (u'-ve-al). That which refers to the vascular 
 layer of the choroid coat, or the ciliary body and 
 iris. 
 
 "y . Abbreviation for vision. 
 
 Vein. A vessel which conveys blood toward the 
 heart. 
 
 Visibility (vis-i-bil'-i-ty) . That which has the capa- 
 city of being seen. 
 
 Vision. The ability of the organ of sight (the eye) 
 to recognize surrounding objects. Double v., (see 
 Diplopia). Binocular v., seeing an object with 
 both eyes at the same time without diplopia. 
 Monocular v., the act of seeing with only one eye. 
 
 Visual. Pertaining to vision or sight. V. Angle, an 
 angle formed by lines drawn from the extreme 
 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 object 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. 
 
OPTICAL DICTIONARY. 193 
 
 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 distance at 
 which an object of given size can be seen, the 
 greater is the acuity of vision the eye possesses. 
 
 Vitreous ( vit'-re-ous) . A transparent fluid occupy- 
 ing the posterior and interior four-fifths of the 
 eye. 
 
 Vitreous Humor. A transparent, colorless, gelatin- 
 ous mass which fills the posterior cavity 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. 
 
 Virtual Focus, An imaginary or negative focus. 
 
 Von Graefe's Sign. That condition where the lid 
 fails to move downward with eyeball in exoph- 
 thalmic goiter. 
 
 W all-eye. This term has several meanings. It 
 generally refers to white opacities of the cornea 
 or a pale blue iris. Sometimes divergent strabis- 
 mus. 
 
 AV'ave Theory. The theory that light travels in 
 waves instead of rays. (See Light). 
 
 Vrink. The act of opening and closing the eyelid 
 suddenly. 
 
 Winker. (See Eyelash.) 
 
 Worsted Test. The common test employed for 
 color-blindness. 
 
 lit 
 
194 LEWIS POCKET 
 
 .-^Xanthelasma (zan-thel-as'-mah). 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. 
 
 Xanthocyanopia (zan-tho-cy-an-o'-pi-ah). That con- 
 dition in which there is an inability to perceive 
 red and green colors. 
 
 Xanthoma (zan-tho'-mah). A yellowish new growth 
 on the skin. 
 
 Xanthophane. A condition in which objects appear 
 yellow. 
 
 Xeroma (ze-ro'-mah). That condition where the 
 conjunctiva is abnormally dry. 
 
 Xerophthalmia (ze-rof-thal'-mi-ah). Conjunctivitis 
 with atrophy and no liquid discharge. 
 
 Xerosis (ze-ro'-sis). Abnormal dryness of the eye. 
 
 i ellow Spot. The macula lutea. 
 
 Young-Helmholtz Theory. The theory that color 
 vision depends on three sets of retinal fibers which 
 correspond to the colors red, violet, and green. 
 
 / ^eiss's Glands. The sebaceous or sweat glands 
 located at the free border of the eyelids. 
 
OPTICAL DICTIONARY. 195 
 
 Zinn*s Ligament. A circular ligament at the optic 
 foramen from which arises the recti muscles of 
 the eye; the ligament itself is attached to the 
 bone and allows the optic nerve to pass 
 through its center. 
 
 Zone. A girdle or belt. 
 
 Zonula. A very small membrane surrounding a 
 body. A small zone. 
 
 Zonule of Zinn. The suspensory ligament of the 
 eye-lens. 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 cili- 
 ary body, but leave it at the apices of the ciliary 
 processes, and, becoming free, divide and pass over 
 to the edge of the lens, thus forming the anterior 
 and posterior suspensory ligaments. These liga- 
 ments are attached to the capsule of the lens 
 with which they become fused. The space, tri- 
 angular in shape, included between tlie 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 sometimes called a Zone of 
 Zinn. 
 
 Zonulitis. Inflammatiou of the Zonule of Ziun, 
 
196 LEWIS POCKET 
 
 RULES TO BE REMEMBERED. 
 
 No. 1. No eye should be allowed to use accommo- 
 dation 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 dis- 
 tant vision. 
 
 No. 6. Before testing for muscle trouble correct 
 the ametropia. 
 
 A. FEW QUESTIONS WITH THEIR ANSWERS. 
 
 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- 
 ence, 
 
OPTICAL DICTIONARY. 197 
 
 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, and must both be brought 
 into play for the same purpose. 
 8o Q. What lens represents the focal strength of 
 the dioptric system of the eye? 
 A. From 62 to 65 -D. plus. 
 9. Q. When 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- 
 
 ^ toms? 
 A. Objective symptoms are what the operator 
 detects without questioning the patient. 
 Subjective symptoms are those described by 
 the patient. 
 
 11. Q. Why does amblyopia cause convergent stra- 
 
 bismus? 
 A. In order to prevent the amblyopic eye from 
 interfering with the vision of the good eye, 
 the patient turns the eye 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. 
 3. 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 
 
 ophthalmoscope, while a plane retinoscope 
 
 cannot. 
 
198 LEWIS POCKET 
 
 14. Q. What lens can be combined with plus I 
 
 sphere combined with plus 1 cylinder, axis 
 90, that will increase the cylinder and de- 
 crease the sphere? 
 A. Any minus cylinder under 2 diopters with 
 its axis at 180. 
 
 15. Q. What is false myopia, and how is it pro 
 
 duced? 
 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. 
 
 Points one should be familar 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; ad- 
 justing same to different persons. 
 
 2. The common shapes and forms and dioptric 
 values of lenses of different kinds; submitting 
 ten different kinds to applicants for determina- 
 tion 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 an instru- 
 ment; the actual doing of this work and deter- 
 mining the error of refraction by the method. 
 The mirror or instrument preferred may be used. 
 
 5. Muscle testing, and the use of muscle 
 testing devices; a test of the applicant's ability 
 to make these tests and draw correct conclu- 
 sions from them and their showings. 
 
OPTICAL DICTIONARY. 19& 
 
 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 muscles of 
 the eyes. 
 
 7. Questions on the anatomy and physiology 
 of the eyes, including muscles, nerves, tissues 
 and their functions. 
 
 8. Questions on refraction of lenses, transpo- 
 sition, conjugate foci, image forming, and the 
 media of the eye. 
 
 9. Questions in optometry, the fitting of 
 theoretical cases embracing all conditions of 
 refraction met in practice. 
 
 10. Questions on the muscles and their 
 anomalies, and the meaning of the different 
 results obtained in practical testing. 
 
 11. Questions relative to cases that lenses 
 do not fully correct; internal or external indica- 
 tions of disease. 
 
 EXAMINATION QUESTIONS. 
 
 1. What is refraction, reflection, diffraction? 
 
 2. What are the principal laws of refraction, 
 reflection? 
 
 3. Give a brief description of the wave theory 
 of light transmission. 
 
 4. What is a ray of light? a pencil? 
 
 5. What do you understand by the following: 
 The optical center of a lens, the center of curva- 
 ture, the normal to a surface? 
 
 6. Describe a lens; name the kinds, and 
 explain how each influences parallel rays of 
 light, together with ametropic conditions each 
 is used to correct. 
 
200 LEWIS POCKET 
 
 7. What do we understand by the terms 
 focus, virtual focus and principal focus? 
 
 8. Name three kinds of mirrors relative to 
 their curvature of surface and tell how each 
 influences parallel Hght rays. 
 
 9. Define the incident, the refracted, the 
 reflected ray. 
 
 10. Define a one dioptre lens, and tell how 
 you would differentiate between a plus and 
 minus lens; also between a sphere and a cylinder. 
 
 11. What is the nodal point; the principal 
 and secondary axis of a lens? 
 
 12. Which ray passes through the lens un- 
 changed, and along what lines does it travel? 
 
 13. What is an angle; right angle; sine of the 
 angle; an arc; and tell which is the greater angle, 
 one whose arc measures -t5^, or one of 90^'. 
 
 14. Define the visual angle and give the size 
 of its angle when required to show 20-20 vision 
 at 30 feet. 
 
 15. Define the term radius of curvature; 
 and explain the difference between the expres- 
 sions *' greater curvature" and ^'lesser curva- 
 ture;" also state which lens has the greater 
 curvature, — ^5D. or — 8D. 
 
 16. Name' three causes which contribute to 
 the determination of the focal point of a lens. 
 
 17. How would you proceed to find the 
 optical center of a lens, the axis of a cylinder, 
 the base apex line of the prism? . 
 
 18. Define the\term '* conjugate foci" and 
 calculate the distance of the object when the 
 image is formed at 15 centimeters, a -f- 5 D, 
 intervening. 
 
OPTICAL DICTIONARY. 201 
 
 19. Give the table for linear measure in the 
 Metric System; the equivalents of the meter and 
 centimeter in inches. 
 
 20. If the curve on one surface of a bi-convex 
 lens is on a 13J inch radius and the other on a 
 40 inch radius, what is the power of the lens? 
 
 21. Why does a distant object, seen through 
 a plus lens, seem to grow in size as the lens is 
 pushed forward? and what is the action of a minus 
 lens under similar conditions? 
 
 22. Transpose the following: — 2 S. O -f .75 
 C. ax. 75. Write two prescriptions for a case 
 of astigmatism, the vertical meridian — 3.75 D. 
 myopic, and horizontal — 75 D. myopic. 
 
 23. Describe the difference between the image 
 formed by the entire lens and one in which the 
 rays must also pass through a pinhole diaphragm. 
 State the clinical signification when the pinhole 
 test fails to improve vision. 
 
 24. What is an image, and how is it formed, 
 and state the position it assumes on the retina 
 relative to the object? 
 
 25. Describe a prism; and tell how the unit 
 of measure, the prism dioptre, is obtained. 
 
 26. By what means and how do we obtain 
 the spectrum, and what does it teach us? 
 
 27. What is chromatic aberration? spherical 
 aberration? 
 
 28. Which glass has the greater dispersive 
 power — crown or flint? and which of the compo- 
 nent rays of white light is influenced most pow- 
 erfully and which the least by the laws of refrac- 
 tion? 
 
 29. Give a brief description of the retinoscope 
 and the principles involved. 
 
202 LEWIS POCKET 
 
 30. Define the character of the shadow and 
 the direction of its movements, in simple hyper- 
 metropia, simple myopia and astigmatism, with 
 plane mirror. 
 
 31. How many methods are there for examin- 
 ation of the retina by means of the opthalmo- 
 scope, and in what particulars do they differ? 
 
 32. In the direct method with the ophthal- 
 moscope, if you are — 2 D. myopic and you get 
 the best view of the fundus through the sight- 
 hole, no lens intervening, and accommodation 
 at rest, what is your patient's condition of re- 
 fraction? 
 
 33. When the eye ground is examined with 
 the ophthalmoscope, under what conditions are 
 each of the tunics visible? 
 
 34. What is the course of light rays, reflected 
 from the posterior part of the eye (the eye being 
 at rest), in myopia, hypermetropia and emme- 
 tropia? 
 
 35. What do you understand by decentra- 
 tion of lens and its relations to the adjustment 
 of spectacles? 
 
 36. Define pupillary distance and tell how 
 you would measure same. 
 
 37. How would you proceed to measure for 
 spectacles? name the principal measurements 
 involved. 
 
 38. What constitutes the dioptric system of 
 the eye? 
 
 39. Give the average dimensions of the emme- 
 tropic eye and the dioptric value of lens neces- 
 sary to neutralize one mm. increase in length 
 of eye beyond that in emmetropia. 
 
OPTICAL DICTIONARY. 203 
 
 40. Define the optic axis of the eye; the visuai 
 line and the angle gamma. 
 
 41. What do you understand by static and 
 dynamic refraction of the eye? punctum proxi- 
 mum and punctum remotum? 
 
 42. Describe accommodation and name the 
 several anatomical parts co-ordinating during 
 the act. 
 
 43. How is the accommodation influenced 
 by age? Give the powers of accommodation at 
 40, 45, 50, and 70 years of age. 
 
 44. What is range or amplitude of accommo- 
 dation, and what do you understand by relative 
 range of accommodation and relative range of 
 convergence? 
 
 45. How may spasm of accommodation affect 
 the refraction of the eye and complicate the tests 
 therefor? Differentiate between tonic and clonic 
 spasms of accommodation. 
 
 46. Give some of the symptoms of hyper- 
 metropia where this condition exists in a mild 
 degree. 
 
 47. What is hypermetropia? Name the con- 
 ditions of the dioptric system that may be the 
 immediate cause of this error in refraction. 
 
 48. What is the state of refraction in myopia? 
 Name the conditions of the dioptric system that 
 may be the immediate cause of this anomaly. 
 
 49. What are the different tests for hyper- 
 metropia, myopia and astigmatism? 
 
 50. How would you proceed to diagnose an 
 error of refraction? 
 
 51. Describe the cornea and its curvature of 
 surface in detail. Give its index of refraction 
 and name the dioptric value of one mm. varia- 
 
204 LEWIS POOKET 
 
 tion in radius of curvature of any one meridian 
 of the cornea. 
 
 52. What is astigmatism, and into how many 
 classes and subdivisions is regular astigmatism 
 divided? 
 
 53. What is irregular astigmatism, and what 
 parts of the dioptric system are at fault? 
 
 54. What is keratometry? 
 
 55. Name the following radii of curvature: 
 The anterior and posterior surfaces of cornea 
 and lens, also the distance of the anterior princi- 
 pal focus from summit of cornea and posterior 
 principal focus from the nodal point. 
 
 56. What is conical cornea and its effect on 
 the refraction? 
 
 57. What constitutes perfect binocular vision? 
 What is the fusion sense? 
 
 58. Define orthophoria and give the tech- 
 nical terms for each condition of heterophoria 
 and heterotropia; and name the tests for hetero- 
 phoria. 
 
 59. Define abduction, adduction, sursum- 
 duction and torsion; and name the muscles func- 
 tioning in each movement. 
 
 60. How would you differentiate between 
 concomitant and paralytic strabismus? and how 
 do they differ in regard to subjective symptoms? 
 
 61. Define paresis and paralysis, and tell how 
 you would diagnose either condition. 
 
 62. What is diplopia, and the cause? Define 
 homonymous and heteronymous diplopia and 
 describe the orientation of the false image in 
 either condition of diplopia. 
 
OPTICAL DICTIONARY. 205 
 
 63. Name the intrinsic and extrinsic muscles 
 of the eye, and the nerves supplying innerva- 
 tions to each. 
 
 64. Define convergence and its relation to 
 accommodation. How would a prism base in 
 affect convergence, base out? 
 
 65. Name the muscles affected in each eye 
 by the following prescription: O. D. + 3.50 D., 
 O. S. + 7.50 D., decentered 2mm. in at meridian 
 135. Denominate prismatic value at primary 
 position of eyes. 
 
 66. What is the iris? Name its functions, 
 also define mydriasis and miosis, naming at least 
 three drugs producing the former and two the 
 latter condition. 
 
 67. Define anisometropia and state how this 
 condition, when marked, complicates the correc- 
 tion of refractive defects. 
 
 68. Describe the crystalline lens; name and 
 describe its functions; give its index of refraction 
 and the refractive effect of extraction. 
 
 69. Describe the character of the vitreous 
 and its functions, and state whether or not the 
 index of refraction is in excess of that of the 
 crystaline lens. 
 
 70 What is the aqueous and its functions? 
 how is it divided and how does its index of re- 
 fraction compare with that of the cornea? 
 
 71. What is the Capsule of Tenon and its 
 functions? What are the check ligaments and 
 their functions? What is the trochlea? 
 
 72. Describe the optic orbit in detail. 
 
 73. Describe the function of the lids and 
 name their muscles, with the nerves dominating 
 
206 LEWIS POCKET 
 
 each. What are the cartilages and their purpose? 
 What are the canthi? 
 
 74. Describe the meibomian glands and their 
 functions. 
 
 75. Of what does the lachrymal apparatus 
 consist? 
 
 76. In what way do the tears escape from 
 the conjunctival sac? and with what cavitiss is 
 this duct continuous? 
 
 77. Describe the ciliary muscle, its ligarneii r-e 
 and functions. 
 
 78. Describe the sclera, and name it^ tum:^ 
 tions. 
 
 79. Describe the choroid, and name its f u'&c- • 
 tions. 
 
 80. Describe the circulatory system of the 
 eye, and name the principal arteries and veins. . 
 
 81. Describe the nervous system of the eye. , 
 
 82. What i« the character of the retina audi 
 its relations to the optic nerve? 
 
 83. What do you understand by acutenessi 
 of vision?. Name and describe the point of most I 
 acute vision in the eye, and name the functions 
 of the peripheral portion of the retina. 
 
 84. What is asthenopia and what causes itf I 
 
 85. Describe leukoma and opacity. 
 
 86. Name the principal diseases of the cptiC: 
 nerve. 
 
 87. Describe the objective and subjectiva 
 symptoms of glaucoma and name certain drugs 
 that have a tendency to precipitate an attack of i 
 this disease. 
 
OPTICAL DICTIONARY. 207 
 
 88. What is the ametropic correction for a patient, 
 ige twenty years, with his near point of the yertical 
 neridian at eight inches and the near point of the 
 lorizontal meridian at ten inches? 
 
 89. What is the correct prescription for distance for 
 . patient, age thirty years, looking at thirteen inches, 
 vith his focus on the retina, while w^earing a + 2 sph. 
 
 - 3 cyl. ax. 90 and using two diopters of accommoda- 
 iion ? 
 
 90. Does an emmetrope always have normal vision? 
 
 91. Put the following prescription back to the 
 'tinoscopic finding, after reversing the shadow from 
 1 inches: 
 
 — .50 sph. O — .25 cyl. ax. 60. 
 
 92. How do we accommodate? 
 
 93. What is amblyopia? myosis? antimetropia? 
 
 94. W^hat is the correction for an eye, with its f ar- 
 oint at eighty inches and the near-point at forty inches 
 •r distance and reading at thirteen inches? 
 
 95. If a patient is presbyopic two diopters and reads 
 ithout any lens at thirteen inches, w^hat is his error of 
 fraction ? 
 
 96. What causes the shadow to reverse in retinoscopy ? 
 
 97. Do we always improve sight in correcting hyper- 
 etropia? State reason for your answ^er. 
 
 98. How^ is latent hypermetropia detected? 
 
 99. Put the following prescription up in toric form, 
 ing a plus six base curve, making two crosses to show 
 ch side of the lens and the power needed in each arm. 
 
 + 3 sph. O — 2 cyl. ax. 90. 
 
 100. When a prism is prescribed for constant wear, 
 e the eyes parallel to each other? 
 
 101. Place a lighted candle forty inches from a plus 
 o sphere, then a distance of twenty inches to a plus 
 e sphere, what will be the conjugate foci? 
 
208 LEWIS POCKET 
 
 Appendix 
 
 A.myosta'sia. Nervous tremor of the musclel 
 Amyosthe'nia. Failure of muscular strength. 
 Anaphoria. A tendency of the eyes upward. 
 Anatropia. That condition in which the eyes tui 
 
 up. 
 An'nular Muscle. A ring shaped muscle (as til 
 
 sphincter muscle of the iris). 
 Arach'noid Sheath. The delicate membrane b 
 
 tween the dura mater and pia mater of the opt 
 
 nerve and capsule of Tenon. 
 Artificial Pupil, One made by an operatic 
 
 (Iridectomy). 
 Astigmom'eter. An intrument for measuring s 
 
 tigm^atism. 
 Astig'mometry. The study of measurement 
 
 astigmatism. 
 Atax'ia. Failure of muscles to coordinate. 
 Atypic Hypermetropia (at-ip'-ik). Irregular Hyp^ 
 
 metropia caused by tumors behind the eye, e 
 
 erting such a pressure on the posterior pole th 
 
 the region of the macula is pushed in front ' 
 
 the principal focus, the eye thus becoming h 
 
 peropic. ]t may be caused by detachment! 
 
 the retina in the region of the macula. 
 Atypic Myopia (at-ip'-ik). Progressive Myopj 
 
 caused by the elongation of the eye. 
 Axial Ametropia. Ametropia that is ^ caused 
 
 the length of the eyeball on the optic axis. 
 Axis of a Mirror. A line which strikes the cent 
 
 of curvature at right angles to the surface! 
 
 called its axis. 
 
 Jjase Curve. The meridian of least refraction, 
 
 the toric side of a lens. 
 Basedow's Disease (See exophthalmic goiter). 
 Bi-Spherical. A lens with a sphere on both sidi 
 
OPTICAL DICTIONARY. 209 
 
 Bruch's Glands. The lymph-follicles of the con- 
 
 juctiva of the lower eyelid. 
 3ruch*s Membrane. The inner layer of the choroid 
 
 coat of the eye. 
 Sruch's Muscle. See Ciliarj'- Muscle. 
 
 L'analic'ulus. A small canal or channel. 
 
 (^ap'illary (hair like). Any one of the little vessels 
 which conduct the blood from the arteries to 
 the veins. 
 
 i^ardinal Points. Points which play an important 
 part in the course of light through a spherical 
 surface. There are four in number. The two 
 principal foci and the two nodal points. The 
 first principal focus is the point from which light 
 r-ays 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 incident 
 rays have been parallel to the principal axis. 
 
 Caustic Curve (kaus'-tik). A curve to which the 
 rays of light reflected or refracted by another 
 curve are tangent. 
 
 ^elluHtis (sel-u-li'-tis). Inflammation of the loose 
 tissues of the orbit. 
 
 Centrifugal (sen-trif'-u-gal). Tending, or causing, 
 to recede from the center. 
 
 Centrifugal Impression, An impression sent from a 
 nerve center outwards to a muscle or muscles by 
 which motion is produced. 
 
 Ciliary Processes. The radiating circular folds 
 composed of a connective tissue stroma, which 
 pass up over the ciliary body. There are abont 
 sixty or seventy in number. 
 
 Conjugate Deviation. The deviation of both eyes 
 in the same direction. 
 
 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. 
 
210 LEWIS POCKET 
 
 Corradiation (kor-ra'-di-a'-shiin). A conjunction oi 
 concentration of rays in one point. 
 
 Corectomy (ko-rek'-to-me) . See iridectomy. 
 
 Cyst (sist). Any sac containing a liquid. Derm-i 
 oid Cyst is congenital. It is a painless, unin-i 
 flammed spheroidal mass, situated generallji 
 at the outer angle of the orbit, on a level with thn 
 
 • outer end of the eyebrow. 
 
 Jjecomposition of Light. If parallel rays of sum 
 light pass through a prism, it is not only re- 
 fracted, but it is also decomposed into its variousi 
 colors. This is due to the unequal • refrangi, 
 bility of the different colored rays which formi 
 white light, the violet being refracted the most 
 and the red the least, thus forming the spectrumj 
 
 Deor'sumvergens. Downward turning of the eye* 
 
 Dura Mater. The outermost membrane of the brainy 
 spinal cord, optic nerve and capsule of Tenon. 
 
 Dural Sheath. The external covering of the optici 
 nerv^e. 
 
 Dynameter (dy-nam'-e-ter). An instrument for 
 determining the magnifying power of telescopes, 
 
 Dynamometer (dy'-na-mom'-e-ter). An instru- 
 ment 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). Inability to read caused 
 by a disease of the brain. Vision is good but the 
 power to read is wanting. 
 
 Dysopsy (dys-op'-sy). Dimness of vision. 
 
 xlimphyse'ma. The infiltration of air into the cellu-* 
 lar tissues of the orbit. May be caused by rupturf 
 of the lachrymal sac. 
 
 Ephidro'sis. An excessive secretion of the sweat 
 glands of the eyelids. It causes itching, irrita- 
 tion and inflammation of the skin and con- 
 junctiva, it is difficult to cure. 
 
OPTICAL DICTIONARY. 211 
 
 ithelio^ma. Cancer composed largely of epithel- 
 %l cells and is the most frequent of malignant 
 
 Irowths affecting the eyelid. It seldom appears 
 
 |efore the age of forty. 
 in'sic. Of exterior origin. E. Muscles are 
 lose on the outside of the organ. 
 Ground. The inside and back part of the eye. 
 
 the Fundus. 
 
 r alse Image. The image seen with the deviating 
 eye. 
 
 ^ascia (fash'-e-ah"). A band or sheet of tissue con- 
 necting and investing muscles. 
 
 ^ocal Planes. Straight lines through the foci 
 perpendicular to the principal axis. 
 
 ^ocus. The point produced by light coming to 
 or going from a point. First Principal 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 incident rays 
 have been parallel to the principal axis. Neg= 
 ative 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. 
 
 hogging 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 (See page 185), 
 
 LxangMon (gang'-gle-on). A collection of nerve cells 
 giving off nerve fibers in one or more directions. 
 A mass of vesicular neurin in the course of a nerve, 
 apart from the brain and spinal cord. 
 
 ionorrhe'al Ophthalmia. The most acute form of 
 purulent conjunctivitis. It is caused b}^ the 
 introduction of the urethral discharge to the con- 
 junctival sac 
 
212 LEWIS POCKET 
 
 Jieterophoral'gia. Pain with heterophoria. 
 Histology (his-tol'-o-je). The sdence of the minute 
 
 structure and composition of tissues. 
 Hutchinson's Pupil. One that is dilated on on© 
 
 side. 
 
 Inflection (in-flek'-shun). The act of bending im 
 ward or that state of being bent inward. 
 
 Ijigamentum Pectinatum. The ligaments which 
 
 pass from the base of the iris to the cornea; 
 
 Through its meshes pass Fontana's spaces. 
 Lymph (limf). A pure transparent fluid like water? 
 
 a coagulable fluid in animal bodies, contained 
 
 in bodies called lymphatics. 
 Lymphatic (Hm-fat'-ik). Pertaining to, of thd 
 
 nature of, containing or conveying lymph. 
 
 JMedian. Situated in the middle. The Median 
 line refers to the line drawn from a point betweeif 
 the two eyes straight forward parallel with th(l 
 two eyes. 
 
 Migraine (mi-gran'). A kind of sickness or nervoua 
 headache, usually periodical and confined to th4 
 side of the head. 
 
 Monochromatic Light. The spectrum is formeo 
 by a prism dividing Hght into its seven colorsi 
 Such light is called Monochromatic Light. 
 
 Myitis (mi-i'-tis). Inflammation of the muscles^ 
 
 Myograph (my'-o-graphV An instrument for re' 
 cording the different phases, such as the velocity: 
 intensity, &c., of a muscular contraction, witl 
 the aid of a registering apparatus. 
 
 Myography (my-og'-ra-phy). A description of mus4 
 eels, including the study of muscular contraction 
 with the aid of a registering apparatus. 
 
OPTICAL DICTIONARY. 213 
 
 Myology (my-ol'-o-ji). 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. 
 
 Myositis (my'-o-si'-tis). Inflammation of the mus- 
 cles. 
 
 Muller's Muscle, Bands of circular fibres situated 
 internal to the radiating muscles in the ciliary 
 bodv. They are sometimes called the *'ring 
 muscle" of MuUer. FIBRES OF MULLER— 
 Are the radiating fibres 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. 
 
 iVegative Convergence. The act of turning the eyes 
 outward from parallelism, by means of the exter- 
 nal recti muscles which turn the eyes outward. 
 Neurasthenia (nuras-then-i'-ah). Exhaustion of 
 nerve force. 
 
 Nodal Points of a Lens. The two points of the 
 principal axis, so situated that every ray which, 
 before being refracted, is directed toward the 
 first of them, seems, after its refraction, to come 
 from the second one, and take 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 re- 
 fracting surface. 
 
 tjcci pit o=Fron talis. The muscle which lifts the 
 eyebrows upward. Supplied by the seventh 
 nerve. 
 
 Ocellus \o-sel'-lus). A single eye. 
 
 Ophtharmia Neonatorum. A form of purulent 
 conjun^.tivitis which attacks newly born children. 
 
'?14 LEWIS POCKEr 
 
 Optical Center of a Lens. The center of refraction 
 It is found by making two parallel radii o 
 curvature, and connecting the points in whicl 
 they meet the surfaces. The point at whicl 
 this line cuts the principal axis, is the optica 
 center. 
 
 Optology (op'-tol-o-ge). See optometry. 
 
 Orb. A spherical bodyo 
 
 J: aracente'sis. Surgical puncture of a cavity. 
 
 Perimetry (pe-rim'-et-re). Measurement of the 
 visual field. 
 
 Pia Mater. The innermost membrane of the brain 
 and spinal cord, optic sheath and capsule of 
 Tenon. 
 
 Polariscope. An instrument used in showing the 
 phenomena of the polarization of light. 
 
 Principal Planes. Straight lines which pass through^ 
 the principal points, perpendicular to the prin- 
 cipal axis. 
 
 jLvecomposition of Light. The reuniting of the colors' 
 of the spectrum so as to produce white Hght. ^ 
 It is done by placing a second prism exactly Uke 
 the first with its apex turned in the opposite 
 direction. The light will be recomposed and will 
 emerge from the second prism as white light. 
 
 Ret'roscopic Lens. A lens that is tilted inward 
 at the top. 
 
 Rules for Refraction. In order to obtain the radius 
 of curvature of any media multiply the focal 
 length desired by the difference of the index in the 
 two media. 
 
OPTICAL DICTIONARY 2l4a 
 
 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 
 curvature and give it the sign of the curve of the 
 denser media. Remember two meter curves in 
 optics means 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 re- 
 fraction of the second media. 
 
 {Sclerotomy (skle-rot'-o-me). Surgical incision of 
 the sclera. 
 
 Se'cant (In Geometry). A line that cuts another, 
 or divides it into parts. The secant of a circle 
 ■ is a hne drawn from the circumference on one 
 side to a point on the outside of the circum- 
 ference on the other. 
 
 Spectrum (spec'-trum). The seven primary colors 
 of which light is composed, separated after pass- 
 ing through a prism together form the solar 
 spectrum. The colored rays of which light is 
 composed become separated by the refraction 
 of a prism or other means. Of the seven colors 
 which form the spectrum Violet is refracted the 
 most, then Indigo, Blue, Green, Yellow, Orange 
 and Red the least. 
 
 Diffraction spectrum is a spectrum produced by 
 diffraction. 
 
 Chromatic spectrum is the visible colored rays 
 of the solar spectrum, showing the seven princi- 
 pal colors in their order and covering the larger 
 portion of the space of the whole spectrum. 
 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. 
 
2U5 LEWIS POCKET 
 
 TLangent (tan'-gent). (In geometry). A line which 
 touches a curve at right angles to its surface, 
 but does not cut it. (In trigonometry the tan- 
 gent of an arc is a right angle line touching the 
 arc at one extremity, through the center and 
 through the other extremity.) 
 
 Tropom'eter. An instrument for measuring the 
 movements of the eye. 
 
1 
 
 OPTICAL DICTIONARY. 215 
 
 Transposition 
 
 To transpose an optical prescription is to change the 
 form or shape of the lens without changing its optical 
 value. 
 
 Writing a prescription from a cross is not transposing. 
 We must first have a written prescription before it can 
 be transposed. 
 
 In order that you may be able to give your patients 
 glasses which give them the best possible results, it will 
 be necessary for you to know how to build lenses of 
 different shapes, for instance: 
 
 Biconvex, biconcave, piano convex, piano concave, 
 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 mer- 
 idians. 
 
 A meridian is any straight line* drawn from edge to 
 edge over its optical center. 
 
 Cut showing how the meridians of an eye are numbered 
 from right to left. 
 
 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 meridians 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 wHl use a plus four sphere 
 and plus four cylinder for example: 
 
216 
 
 LEWIS POCKET 
 
 ^SSS^^^:;^ 
 
 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 instance, we take the following 
 prescription : 
 
 + 4 sph. C + 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 cylinder on the other and cut 
 it out, so that the axis of the cylinder will be at 180 
 degrees. This lens being plus on both sides is known 
 as a biconvex lens. 
 
OPTICAL DICTIONARY. 
 
 217 
 
 In this example we have the sphere and cylinder 
 separated and together, showing their combined 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 prin- 
 cipal meridians. 
 
 In oixler 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. C + 4 cyl. 
 ax. 180 transposed gives you + 8 sph. C — 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. 
 
 . This shape lens is much preferred by the Refractionist 
 of to-day on account of its appearance and comfort 
 to the patient. 
 
218 
 
 LEWIS POCKET 
 
 Prescription No. 2 : — 3 sph. C — 2 cyl. ax. 45. 
 ^Ihis prescription calls for — 3 sph. and a — 2 
 to be ground together. 
 
 l^sr 
 
 This diagram shows the sphere and cylinder separ 
 and together and their appearance from the side. T 
 lens being concave on both sides is known as a biconcj 
 lens. 
 
 In order to make it periscopic we will use the sa 
 rule as before as the signs are alike. 
 
 Prescription : — 3 sph. O — 2 cyl. ax. 45. 
 
 Transposed: — 5 sph. O + 2 cyl. ax. 135. 
 
OPTICAL DICTIONARY. 
 
 219 
 
 That is when the signs are alike add the values to- 
 i sther for the new sphere, which will be — 5, keeping the 
 lime sign. Change the sign of the cylinder, but not 
 s value and change its axis 90' (by adding 90 to 45). 
 his gives us an axis of 135'. 
 
 I When your prescription reads minus and plus your 
 i ns will be periscopic. 
 A prescription thus: + 5 sph. C — 4 cyl. ax. 90, will 
 
220 
 
 LEWIS POCKET 
 
 be ground, and in order fo change its shape it must t 
 transposed by the following rule: 
 
 When the signs are unlike that is, one plus and th 
 other minus, subtract for your new sphere thus: 
 
 Example: + 5 sph. C — 4 cyl. ax. 90. 
 
 Transposed: + 1 sph. C + 4 cyl. ax. 180. 
 prefixing the sign of the larger number and change t| 
 sign of your cylinder, as it was minus we make it pliji 
 but .do not change its value. Char e the axis 9| 
 but never let your axis run above 180°. If your a,^) 
 was above 90° subtract 90° from it and you have rigl^ 
 angles. On the other hand, if the axis was below 1 
 you add 90° to it. 
 
 Cross cylinders + 2 cyl. ax. 180 C + 3 cyl. ax. { 
 in this prescription we have two cylinders with the 
 
 axes at right angles to each other, and it will be notici 
 that the power of one cylinder lies on the axis of t 
 other. In this way, both cylinders keep their full valil 
 In order to transpose cross cyhnders into spheii 
 cylinders (if the signs are alike) take the smaller cyhndi 
 and call it a sphere and forget its axis altogether. Th^ 
 
OPTICAL DICTIONARY. 
 
 221 
 
 ;ake the difference between the two fo" the new cylinder 
 keeping the same sign and axis. 
 
 Example: + 2 cyl. ax. 180 C + 3 cyl. ax. 90. 
 
 Transposed: 4- 2 sph. C + 1 cyl. ax. 90. 
 
 i%0' 
 
 tL. 
 
 +^ 
 
 .±1 
 
 ^r 
 
 % 
 
 /io- 
 
 Simple Cylinders 
 
 5!xample: +2, Cyhnder axis 90 degrees. 
 o 
 
 t 
 
 ^■x_ 
 
 jo- 
 
 in order to transpose this prescription, just call the 
 ylinder a sphere of the same value and combine with 
 
222 
 
 LEWIS POCKET 
 
 it a cylinder of the same value, but the opposite sign 
 and change its axis 90 degrees. 
 
 Example: +2, Cylinder axis 90 degrees. 
 
 Answer: +2, Sphere, combined with - 2, Cylinde: 
 axis 180 degrees. 
 
 ,/tr 
 
 -A 
 
 y^j 
 
 -±i_ 
 
 _±A- 
 
 fSrO 
 
 These cuts show the two lenses separate and coddi 
 bined, and also the side view. 
 
 Neutralizing is doing away with power in lenses b 
 the act of placing minus and plus together. Puttii 
 lenses with the same sign together, their values ad( 
 but when the signs are different, they neutralize, lea 
 ing the difference between the two, with the sign of tl 
 larger number. This fact must be remembered wh( 
 combining lenses. 
 
 Every cylinder has one flat or plain meridian, whi( 
 is called its axis. Right angles to its axis it has i 
 greatest curvature (or power), and whenever a cylind 
 is placed on a sphere, the sphere will keep its value 
 the meridian which is covered by the axis of the cylindC 
 It depends upon the power of the cylinder what chani 
 will be made in th^ sphere at the meridian, right ang^ 
 to the axis o^ t> ylinder. 
 
OPTICAL DICTIONARY. 
 
 223 
 
 To write a prescription from a cross, take the power 
 that is written on either arm with the same sign for 
 your sphere. This being a sphere, it will put the same 
 power in all meridians and if the powers on the arms 
 of the cross are different, it cannot correct them both, 
 and the cyhnder that you use must represent the 
 difference between the two. 
 
 In this case, we will take the plus two for the sphere. 
 
 + 3L 
 
 /ro 
 
 90' 
 
 This will correct the vertical or ninetieth meridian, 
 while it will under-correct the horizontal by two diopters, 
 which will call for a plus two cylinder, axis ninety de- 
 grees, combined with the plus two sphere. 
 
 Example: +2.00 Sphere combined with +2.00 
 Cylinder axis 90 "degrees. 
 
 +2. 
 
 -±i 
 
 -fa. 
 
 /fo- 
 
 ±Jl 
 
 90' 
 
224 
 
 LEWIS POCKET 
 
 These two combined together give us tnc w.amc 
 power as that called for on the cross. 
 
 When we take the plus four for the sphere, we over- 
 correct the vertical meridian by two diopters, there- 
 fore, it will be necessary to combine a minus two cylin- 
 der axis 180 degrees in order to get the desired result. 
 
 tli 
 
 fOSph. 0-3Cyl. ax. 90' — 3 Sph. O + 5 Cyl. ax. 90' 
 +3 Sph. o +3 Cyl. ax. 180 +2 Sph. a -5 CyL ax. 180' 
 
OPTICAL DICTIONARY. 
 
 225 
 
 - ^7S 
 
 Jjo' 
 
 + 3 Cyl. ax. 45 
 
 + 3 Sph. 0-3 Cyl. ax. 135. 
 
 90' 
 
 3.75 Cyl. ax. 180. 
 
 3.75 Sph. O + 3.7f. Cyl. 
 
 ax. 90. 
 
 The Advantages and Make of 
 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 appHed 
 to a lens having 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 other side of the lens may be either 
 piano, concave or convex; but they are usually made 
 extra deep periscopic. 
 
 To give an idea of the appearance and proper uses 
 of such lenses, I will put up prescriptions for the five 
 subdivisions of ametropia which can be corrected by 
 lenses in toric form. This can best be explained by 
 diagrams. 
 
 The first prescription will be for compound hyperopic 
 astigmatism + 3 sph. O + 2 cyl. ax. 90. 
 
 This lens when ground must refract plus three diopters 
 in the ninetieth and plus five diopters in the one hun_ 
 dred and eightieth meridians, independent of its shape* 
 
'226 
 
 LEWIS POCKET 
 ^3 . 
 
 ■J^ 
 
 But in order to get a deep periscopic effect, the ad- 
 vantage of which I will explain later, suppose we grind 
 one side of the lens thus: 
 
 + 16 
 
 •^<9. 
 
 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. 
 
 The next is a prescription for simple hyperopia astig- 
 matism: + 3 cyl. ax. 45. 
 
 In this lens you require plus three diopters in the 
 one hundred and thirty-fifth meridian and no power in 
 
OPTICAL DICTIONARY. 227 
 
 the forty-fifth meridian. The difference between the two 
 being three diopters, on one side of the lens we will grind 
 
 plus six diopters in the forty-fifth meridian and plus 
 nine diopters in the one hundred and thirty-fifth meri- 
 dian, and on the other side enough minus sphere to 
 neutralize all the power from the, forty-fifth or weakest 
 meridian, which will be a minus six sphere, leaving the 
 lens the required strength and shape. 
 
 Prescription for compound myopic astigmatism: 
 - 2 sph. O - 2 cyl. ax. 180. 
 
 -=:S. 
 
 This prescription calls for a minus two diopters in the 
 one hundred and eightieth meridian and minus four 
 diopters in the ninetieth; the value of the cylinder being 
 two diopters. We will grind on one side minus six diopters 
 
 -s. 
 
 -6. 
 
 /go- 
 
 ?0' 
 
228 LEWIS POCKET 
 
 in the one hundred and eightieth meridian and minus 
 eight diopters in the ninetieth meridan, leaving the 
 cyHndrical value of 2 D. between the two; on the 
 other side we grind a plus four sphere. This will give 
 us the desired result in toric form. 
 
 Prescription for simple myopic astigmatism: - 4 
 cyl. ax. 150. 
 
 This prescription calls for minus four in the sixtieth! 
 meridian and no power in the one hundred and fiftieth! 
 meridian; the difference in the two neutralizes four 
 diopters. We grind on one side minus six diopters 
 
 V 
 
 in the one hundred and fiftieth meridian and minus 
 ten diopters in the sixtieth meridian; and on the other 
 side we grind a plus six sphere which will neutrahze 
 minus six diopters from all meridians, leaving the lens 
 the desired strength and at the same time give us a 
 deep periscopic lens. 
 
 Prescription for mixed astigmatism: + 1 sph. O 
 -3 cyl. ax. 90. 
 
 This prescription calls for a lens that is plus one 
 diopter in the ninetieth meridian and minus two diopters 
 in the one hundred and eightieth meridian. 
 
OPTICAL DICTIONARY 
 
 2^ 
 
 no' 
 
 90- 
 
 The difference between the two principal meridians 
 being three diopters, we will grind on one side of the 
 lens a plus six diopter in the one hundred and eightieth 
 meridian and plus nine diopters in the ninetieth meridian* 
 
 + 9 
 
 _±6, 
 
 /StP/ 
 
 On the other side we will grind a minus eight sphere 
 which will neutralize all the plus from the one hundred 
 and eightieth meridian (leaving minus two power) and 
 plus eight from the ninetieth meridian, leaving plus 
 one diopter, the desired strength required. 
 
 It will be noticed that I have used a plus six or a 
 minus six for the weakest curve on the toric side. This 
 is known as the base curve, and it is used in eighty per 
 cent, of the toric lenses to-day, as this permits the whole- 
 sale houses to carry a stock of lenses with the toric 
 curves already ground, thus cheapening the prices of 
 toric work. 
 
230 
 
 LEWIS POCKET 
 
 Very often prescription houses receive prescriptions 
 calling for a toric sphere, when an extra deep periscopic 
 lens is required, but not of toric shape, which would 
 cost four times the price. For instance, suppose we 
 require a plus two sphere and order it toric. It could 
 be made plus six in one of its pricipal meridians and 
 plus eight in the other. 
 
 +Sr 
 
 -t^ 
 
 no' 
 
 90 
 
 And on the other side minus four diopters in one 
 meridian and minus six in the other meridian. The 
 two sides combined would give the desired result, a 
 plus two sphere, but it would be a very expensive form 
 whereas it would be only one-fourth the price if it were 
 to be ground as a plus six sphere on one side and minus 
 four sphere on the other, which would be the same 
 dioptric value. It is never advisable to order real toric 
 spheres. 
 
 When lenses of high power are required, say +16 
 sph. O + 4 cyl. ax. 90, it is best to divide the power in 
 the following manner, and at the same time obtain a 
 toric lens. 
 
 The prescription calls for plus sixteen diopters in 
 the vertical meridian and plus twenty diopters in the 
 one hundred and eightieth meridian. 
 
OPTICAL DICTIONARY. 
 
 2:^1 
 
 ■fXQ 
 
 ?o 
 
 We win grind on one side of the lens, plus six in the 
 90th meridian and plus ten in the 180th; and on the 
 
 /J>t> 
 
 +t. 
 
 -t/o. 
 
 ?o- 
 
 other side a plus ten sphere, which would give the de- 
 sired result. The same may be done with strong con- 
 cave lenses, this making them biconcave. 
 
 When a toric lens is desired, it is not necessary for 
 the refractionist to mention the curvature. For the 
 sake of simplicity, just WTite the word * 'toric" beneath 
 the description of the lenses in your prescription. Then 
 write the prescription in the usual way. 
 
 Toric lenses are more expensive than the old form 
 of lenses, but on account of their superiority they are 
 coming more into general use. 
 
 In the first place they allow a greatly enlarged fiild 
 
or 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 typo, 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 periscopic 
 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 prismatic effect. 
 
 The diagrams will show the shape of the two kinds of 
 lenses from the same prescription, + 2 sph. O - 1 
 cyl. ax. 90. 
 
 Again, the edges of the lenses come nearer to the face, 
 thus adding to the patient's appearance. 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. 
 
MEMORANDUM 
 
MEMORANDUM 
 
 
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