EJIKEIEY I.1BRARY lij-'iivtRsiTY or CAIIPORNU DONATED TO AOA LIBRARY BY: Dr. Gordon C. Shlvas Madison Street Pulaski, Tennessee propertKof mmm 7000 C\m^^^ 5^''^^^"^ I r V "J^-V^ \J\^ ^ SUPPLEMENT TO THE OPTICIAN'S Manual Copyright, 1S99, by B. Thorpe Publisher of The Keystone SUPPLEMENT TO THE OPTICIAN'S Manual CHAPTKRS 11 AND 12. A Treatise on the Science and Practice of Optics, COMPII^KO FROM TIIH SKKIAI, WRITTEN' HY C: H^Brown, m. d., Graduate I 'nivetsily of Pennsylvania ; Piojessot of Optics and Refraction : formerly Physician of the Philadelphia Hospital; Member Philadelphia County, Pennsylvania State and American Medical Societies. Published Exclusively in Tin. Kkvstonk, the Organ of the Jewelry and ()j)tical Trades. WITH ILLlJSTRATIOiNS. PrBI-ISlIKO BY THK KKVSTONE. 19TH AND Brown Strkkts, Phil.\dei,phi.\, Pa., T. S. A. 1899. ^r 0?XO\-Z,K OPrO f'rkface:. T^HIS Supplement to "The Optician's Manual" has been *- compiled in response to repeated and ury^ent requests that we republish in book form the two chapters of TiiK Kkvstone serial which covered the important subjects of Hypermctropia and Myopia. These two chapters are a direct continuation of the matter published in the Manual, and all who have read them concede that there is no book available to the optician in which Hypermctropia and Myopia have been treated so clearly and exhaustively. As in the case of "The Optician's Manual," the matter is written in such a way as to be readily intelligible to the beginner, while containing all the information needed by the experienced optician. In presenting this Supplement, we are happy in having the endorsement beforehand of the profession at large, including optical teachers, students and practitioners. ozrz COXTKX' Chapter 11. HYPERMETROPIA 11 History of Hypermetropia. Characteristics of Hyperme- tropia. Hypermetropia Hereditary. Divisions of Hyper- metropia. Theory of the Correction of Hypermetropia. Accommodation of Hypermetropia. Latent Hyperme- tropia. The Ophthalmoscope and Hypermetropia. Vis- ion and Hypermetropia. Estimation of the Total Hyper- metropia. Latent vs. Manifest Hypermetropia. Hyper- metropia in Children. Testing Hypermetropia. Metliod by Over-correction. Spasms of Accommodation. What Glasses to Prescribe. Why Glasses Should be Worn. Rules for Determining the Glasses. Proper Fit of Glasses. Sequalec Hypermetropia. Hypermetropia and its Rela- tion to Neuralgia, Spasms of Accommodation, Blepharitis, Styes, etc., Glaucoma, Cataract, Myopia, Asthenopia, Strabismus, Retinitis, Neuritis and Nervous Derangements. S / Chapter 12. MYOPIA 114 Forms of Myopia, Causes of Myopia, School Statistics, Why Children are more prone to Myopia, Myopia Heredi- tary, Preventive Measures, Vision of Myopes, Determina- tion of the Existence of Myopia, Diagnosis of Myopia, Myopia and Amblyopia, Can Myopia be Cured ? Does Age Improve the Myopic Eye? Second Sight, Progressive Myopia, .Apparent or Accommodative Myopia, Symptoms of Myopia, Prevention of Myopia, Tests for Myopia, Treatment of Myopia, Prescribing Glasses for Myopia, How Myopia Disturbs the Normal Relation Existing between Accommodation and Convergence, Treatment of the Muscular Insufficiency accompanying Myopia, Muscle Tests, Surgical Treatment of Myopia, Myopia in Relation to Eye Strain. CHAPTER XL IIVPERMETROPIA. Having given a careful representation of the anatomy of the eye and the physiology of vision, as well as of the simpler laws of optics and the properties and uses of lenses, and having enumerated the outfit required and given minute directions as to the method of examination of a case of supposed optical defect, together with a detailed description of the loss of ac- commodation and the diagnosis and treatment of presbyopia and its complications, we pass on to the consideration of the various optical defects. Tlie first one to be studied will be hypeniwtropia, as being perhaps the error of refraction with which the optician meets most frequently. The word hypermetropia is made up of three Greek words, signifying in excess of the lueasitre of the eye. It may be defined as that condition of the eye-ball, in which the antero-posterior (from in front backward) axis of the ball is too short; in other words, the globe of the eye is too flat, which is equivalent to its refracting power being insufficient, so that parallel rays of light entering the eye cannot be brought to a focus upon the retina when the accommodation is at rest, as it should be when we are looking at distant objects. HISTORY OF lIVPERMKTROriA. Although hypermetropia had been mentioned and de- scribed bv previous writers somewhat indefinitely, it was re- served for Bonders to reduce the knowledge concerning it to 12 HYPERMETROI'lA. scientific accuracy; but it was not until 1848 (less than half a century ago) that he published his first description of this defect, and cleared the optical atmosphere surrounding it, which had pcrviously been cloudy and misty with speculation and error. The elucidation of this hitherto mysterious defect was the magnificent result of many years of patient toil and sys- tematic investigation of the subject, in the light of the knowl- edge concerning it which was at that time the property of the scientific men of the day, together with the added fruit of Bonders' own research and discovery, just as many other great truths have been evolved by a similarly slow process but by a persistent application, such as has characterized the labors of many of the great minds of the age. Previous to this time many affections of the eye were misunderstood, because of the imperfect knowledge of these matters available at that day, and were supposed to have their origin in the nervous system of the eye. In the light of our present knowledge, however, many of these cases were hyper- metropic, and the distressing symptoms were caused by the strain imposed upon the accommodation in its unaided efforts to overcome the defect. DONDERS' OWN W^ORDS. "He who knows by experience how commonly hyper- metropia occurs, how necessary a knowledge of it is to the correct diagnosis of the various defects of the eye, and how deeply it affects the whole treatment of the oculist, will come to the sad conviction that an incredible number of patients have been tormented with all sorts of remedies, and have been given over to painful anxiety, who would have found im- mediate relief and deliverance in suitable spectacles. "It is a great satisfaction to be able to say that asthenopia need now no longer be an inconvenience to any one. In this w-e have an example, by what trifling means science sometimes obtains a triumph, blessing thousands in its results. The dis- covery of the simple fact that asthenopia is dependent on the hypermetropic structure of the eye, pointed out the way in which it was to be obviated." HYPERMETROPIA, 13 PROF. BONDERS Is one of the best-known men conneced with the ophthal- mology of the preceding- generation, and his name is a familiar one to every optical student of the present day. His death was an irreparable loss to ophthalmology and to optics, w^hich is shared and felt by every individual practitioner and worker in this field. But it has been truthfully said by one of his biographers that "we do not lose the master, since his works remain and will always remain, forming the life, the soul of ophthalmology." . /^ I'HOV. DONUEI Donders pursued a medical course, and at the early age of twenty-two years occupied a teacher's chair, followed two years later by his elevation to the professorship of anatomy and physiology in the University of Utrecht, from which he had so recently graduated, and in which he continued during all of his active professional life, building up an international reputation that was limited only by the size of the world, and making of this little city of Utrecht a scientific center that emitted its radiance in every direction, and attracted the at- tention of learned men of every clime. Donders was indeed a foremost representative of Holland in the noble galaxy of savants that were cultivating the fertile fields of science. Donders did not confine his researches to any one portion of the field, but his labors extended over the whole domain of 14 HYPERMETROriA. science, in which are found everywhere the evidences and results of liis indefatigable investigations. lUit to us, as opticians, he is best known and most revered for having enriched our science as no man before or since has done, and particularly through the medium of his great work on the accommodation and refraction of the eye, the fountain of knowledge from which every writer and teacher on the subject draws his inspiration. Bonder's preference in his work was always for teaching, and he is said to have possessed in an eminent degree all those essential qualities which go to make up the perfect professor. "An erudition as profound as extensive; an excellent memory; an intelligence capable of adapting itself to his audience; a wit which colors abstract matters; a rich flow of language; a voice sonorous and flexible; gesture noble and significant; something sublime emanated from the man; physically grand and beautiful, something at once imposing, captivating and sympathetic; great knowledge and great desire to impart it." DOXDERS' IMODESTV. It seems as if Bonders' learning was equaled only by his modesty, and the latter quality is scarcely less an element of greatness than the former; it certainly increases one's ad- miration for the man. Several instances exemplifying this trait of his character are related, and they are so distinctive of the man as to bear repetition. On one occasion an admirer was felicitating him on the discovery of astigmatism, w-hen he made the following mag- nificent reply; "Pardon me, my friend, astigmatism was known a long time before my day; I only discovered astig- matic people." When the time came for Bonders, on account of the limitations which age imposed upon him, to retire from the professor's chair, which he had honored for so many years, it was made an occasion of paying special homage to his merits by his countrymen, pupils and admirers. His modest response to all the glory which was sought to be showered upon him was, "Talk not to me of my merits, but congratulate me on mv luckv star." IIYPERMETROPIA. 15 CHARACTERISTICS OF A 11 VI'ERMETROI'IC EYE. Hypermetropia may be looked upon as a congenital de- fect, in fact the statement has been made that all babies are born hypermetropic. It is supposed to be due to an arrested development in the formation of the eye-ball, which may vary from the slig-htest degree to an extreme condition of small- ncss. The hypermetropic eye differs somewhat from an em- metropic eye, and the following have been enumerated as some of the characteristic points of an eye suffering from this defect. The eye is said to look smaller, but this is a change that is not always noticeable, although as a matter of fact the ball is smaller than the normal eye in all of its dtmensions, but particularly antero-posteriorly. The lens and iris advance for- ward, which makes the anterior chamber shallow^er. Tlie pupil is small and contracted. The ciliary muscle, by reason of its action on the accom- modation, upon which the eye depends for whatever clear vision it may enjoy, is much larger and more fully developed than in emmetropia, this development being particularly noticeable in the anterior portion, which is composed chiefly of circular fibers, and is due to the constant strain imposed on the accommodation by the hypermetropia. On account of the constant relation existing between the accommodation and the convergence (as has been fully ex- plained in the previous chapters) this excessive accommoda- tion is apt to cause an excessive convergence, the result being a case of convergent strabismus. In hypermetropia of high degree, the optic nerve is diminished in size and contains a less number of fibers, which accounts for the lessened acutcness of vision so often found in these cases. In this defect the face is said to have a characteristic flat appearance, the nose depressed, orbits shallow, and the dis- tance between the eyes to be increased. It should be re- marked, however, to the optician that these points are often absent, and thai there may be no distinctive features apparent in the face. 16 HVPERMKTROPIA. It is not unusual to find a liypermetropic eye disposed to astigmatism. HYPERMETROPIA HEREDITARY. It is not an infrequent occurrence to find many members of the same family aifected with hypermetropia. This is so commonly the case that when the diagnosis of hypermetropia is reached in the examination of a patient, the question natu- rally presents itself in the examiner's mind as to whether some other members of the family are not similarly affected; and when this question is put to the patient, the answer generally corroborates the assumption, at least to the extent of admitting that one or both parents commenced to wear convex glasses for reading at a very early age. (Hypermetropia in some cases first shows itself as an early presbyopia, as remarked in the last chapter.) Cases will sometimes be met with in which one eye is em- metropic, and the other eye hypermetropic; and in such cases there may be a' very marked difference in the form of the bones on the two sides of the face, thus illustrating the shallowness of the orbits and the flatness of the face with the diminished prominence of the nose, which so often accompanies and in- dicates hypermetropia. A writer relates a case of this kind, the patient being a young lady who presented herself for treat- ment of stricture of the nasal duct. The lack of symmetry between the two sides of the face and in the size of the eye- balls was strikingly noticeable, and an examination showed the presence of hypermetropia in one eye. It will be remembered that the normal or emmetropic eye, when the accommodation is at rest, is accurately adapted for parallel rays, which come to a focus on the retina, forming on this membrane sharply defined images of distant objects, from which these rays emanate. This is accomplished without any action of the accommodation, which is left unrestricted for its normal purpose of adjusting the dioptric apparatus of the eye for the divergent rays issuing from objects close at hand. In hypermetropia, on the contrary, we find the dioptric system of the eye, when the accommodation is suspended (this is a supposed condition, however, and one that seldom occurs, IIVrKKMKTROriA. 17 because in this defect the acconiinodation is in active and con- tinuous use), on account of the shallowness of the ball, ar- ranged for the refraction of convergent rays, as no other form of rays can be united on the retina in the production of a clearly defined image. Now it is a well-known fact that in nature all rays of light are either parallel or divergent, and hence the hypermetropic eye, being conformed for convergent rays, is adapted for a condition which does not naturally exist. THE FAR POINT IN HYrERMETROPJA. In emmetropia the far point of distinct vision is situated at infinity, or at any distance far enough removed from the eye that the rays proceeding from it shall be parallel. While in hypermetropia, on account of the adaptation of the eye for the imnatural convergent rays, the far point is negative, or may be said to be situated beyond infinity, if such a condition can be imagined. In emmetropia the parallel rays are united on the retina, and distinct vision is the result; in hypermetropia these same parallel rays strike the retina before they have converged to a focal point, which renders distinct vision an impossibility, because each point of the image is surrounded by diffusion circles, and these circles from points of the image close to- gether overlap each other. DEFINITION OF IIYFERMETROPIA. Hypermetropia may then be defined as that condition of the eye in which there is a shortening of the antero-posterior diameter of the ball, or the positive refracting power of the eye is deficient, and the result in either case is that the focus is behind the retina. Or, in other words, the diameter or length of the eye-ball is less than the focal length of its dioptric apparatus. THE DIFFICULTIES OF HYPERMETROPIA PRACTICALLY DEM- ONSTRATED. A concave lens is a negative lens and diminishes refrac- tion; a hypermetropic eye is one in which there is naturally a deficiency of refraction. Now if we consider these two facts 18 IIVl'KRMKTROPIA. together, it folk^ws tliat a concave lens placed before an em- metropic eye will lessen its refraction, and to that extent will make it equivalent to, and place it in the same optical condi- tion as, a hypemietropic eye. Therefore if any one enjoying emmetropic eyes desires to experience a practical demonstra- tion of the difficulties and hindrances which are ever present to annoy and harass the hypermetrope, he can very easily place his own eyes in the same condition by making them artificially hypermetropic by the use of concave lenses. If he tries first weak lenses, and by changing them gradu- ally increases their strength, he will in the beginning find that by the exercise of his accommodation he is able to neutralize and overcome the diminishing effect of the concave lenses. Outline of a Hypermetropic Eye, Showing the Focus of Parallel Rays to be Back of Retina. As, however, he gets into the higher numbers, it becomes a more and more difificult task for the accommodation to coun- terbalance these increasing negative lenses. If, in spite of these warnings that the accommodation has reached the extreme limit of its powers, and its greatest effort is required to preserve vision clear through the concave lenses, a step farther be taken with stronger glasses, it would entirely drain all the resources of the ciliary muscles, and they would be no longer equal to the task of supplying the necessary re- fractive power, and vision would become blurred, and the eyes would be in a condition of absolute hypermetropia. Convex lenses sufficiently strong placed before the con- cave ones, would supplement the exhausted accommodation, and would partly or wholly nullify the diminishing effect of the concave lenses, and distant vision would again be restored clear and distinct. I IIYI'ERMETROPIA. 1^ FORMS OF HVPERMETROl'lA. Hypermetropia ina\ l)c classified as original and acquired. In the acquired funn the eye was primarily emmetropic, but on account of the lessening of its refraction, toward which all its senile changes tend, the focus for parallel rays falls be- hind the retina, and the refraction of the eye passes over from a condition of emmetropia to that of hypermetropia. Tlie changes that take place in the eye with the advance of years, more especially as to the loss of accommodation, and the rationale of the appearance of hypermetropia in old age, have been fully described in the chapter on presbyopia. Original hypermetropia may be either congenital, or de- veloped at a vc'rv early age by an interruption in the growth Ily icriiH'tropie Eyo, Sliowing its Adaptation for Convergent Rays. of the eye, especially in its antero-posterior diameter. The weight of authority seems to favor the opinion that the eyes of new-born babes are hypermetropic, which condition may soon develop into emmetropia, and then pass over into myopia ; and when once these changes have occurred by a lengthening of the axis of the eye-ball, they become permanent, and the ■eye cannot again return to its original hypermetropic condi- tion. This would indicate a tendency for the eye-ball to elongate, and the natural inference would be that myopia is apt to increase, while hypermetropia seldom grows greater, but frcciuently diminishes. T)lVISTOXS OF IIVPEKMETUOIMA. Original hypermetropia may be divided into manitcst and lafcnt, and in order to ascertain the total hypermetropia it is iiecessarv to add the manifest to the latent. 20 HYPERMETROPIA. In hypermetropia of not too high a degree, it is usuall\- found that the distant vision is quite up to the standard, and the sight is apparently that of an emmetropic eye. This is accomphshed by means of the accommodation, which in- creases the convexity of the crystalhne lens and adds to thc- refractive power of the eye, and thus bends parallel rays so as to advance their focus from behind the retina on to this struc- ture. It is the same effect that is produced by a convex lens placed in fro^nt of the eye; and the amount of accommoda- tion required, Nvhich can be expressed by a certain number of convex lens, will represent the degree of hypermetropia present. The division of hypermetropia into- manifest and latent depends on the action of the accommodation ; manifest hyper- metropia is possible only with a suspended accommodation,, w^hile the latent form is that which is concealed by the con- traction of the ciliary muscle. Hence it follows that the more passive the accommodation, the greater the manifest hyper- metropia; and the more active the accommodation, the greater the latent hypermetropia. The manifest hypermetropia is usually apparent without a mydriatic, and is measured by the strongest convex glass that will be accepted for distant vision. The latent defect can be made manifest, or can be detected, only by the use of a my- driatic. As the person advances in life and the power of ac- commodation weakens, in the same proportion the latent defect decreases and passes over intO' manifest, until finally there re- mains no more latent trouble, but it has all become mani- fest. The manifest hypermetropia is, for the purposes of con- venience, written Hm, the latent hypermetropia HI, and the total hypermetropia Ht. ILLUSTRATIONS OF THE DIVISIONS OF HYPERMETROPIA. Perhaps this subject can be made more clear by the ex- emplification of a case of hypermetropia tested at a distance of twenty feet with Snellen's test types. Possibly the eye can distinguish only the larger letters, and the vision would be recorded as follows: V = iVV- If "O'W there is placed before HYPERMETROPIA. 21 the eye a convex lens of 2 D, the vision is raised to normal, and V = |g. In this case the accommodation is supposed to be at rest, and the total hypermetropia (Ht) is 2 D. If, however, the eye would call into action a portion of its accommodative power, the hypermetropia would be corrected thereby and the vision raised to |J without the employment of a convex lens, and this is usually the state of affairs as it is found in young hypermetropes. If now the eyes are tested with convex lenses, the vision remains the same, so that we hnd \' = |§ either with or without convex lenses. This illus- trates manifest hypermetropia, and the strongest convex lens through which vision still remains |§ would represent the degree of manifest hypermetropia (Hm). Tlie record of this case would read V = 3^, Hm. = + i D. That is to say, vision is normal or |g, and remains as good when a convex lens of i D is placed before the eye. Now in this case we presume that a certain amount of the defect is latent or concealed by the action of the accommo- dation, because the patient is unable to completely relax it. In this imaginary case we have a total hypermetropia of 2 D.. and a manifest hypermetropia of i D., and therefore the difference between the two would indicate a latent hyper- metropia of I D. The latent hypermetropia can seldom be revealed except "by the use of atropine, and we would remark in passing that this is not always necessary for the following reason : we can scarcely ever give a glass to do more than correct the manifest hypermetropia, which can be measured without the use of the drug; why then should it be considered essential to determine the latent defect, which after all will not bear correction? THEORY OF THE CORRECTION OF HYPERMETROPIA. It would be theoretically correct to place before hyper- metropic eyes, convex glasses of such strength as to com- pletely neutralize the error of refraction and correct the total hypermetropia, thus giving to parallel rays the degree of con- vergence for which the refractive media are adapted, and in this manner obviating the necessity for calling into action any part of the accommodation for vision of distant objects, so as 22 IIVrERMETROriA. to leave the entire accommodative power unimpaired for the necessary adjustment of the eye for the divergent rays proceed- ing from small objects close at hand. This would be the ideal method of correction of this oftentimes distressing defect. Although it would seem to be the proper thing in hyper- metropia to prescribe such glasses as would completely cor- rect the defect, yet practically such a method of procedure has been found not to answer, except in but few cases, and even then not until after repeated trials with glasses, and not until the eyes have adapted themselves to their use. THE OBSTACLE IN THE WAY OF THE COMPLETE CORRECTION OF HYPERAIETROPIA. The hypermetropic eye, ever since it commenced to fulfill its function in looking at the lettered blocks and picture books of childhood has been accustomed to associate with the act of vision a certain amount of muscular action, or, in other words^ a definite contraction of the ciliary muscle to overcome the defect, for only by this means is the hypermetropic eye able to enjoy clear and distinct vision; and as the natural instinct of the eye impels it to produce Avell-defined vision if within the range of its possibility, this effort of the muscle of accom- modation is purely an automatic and involuntary one, and is ever present, from the time the dawn of morning opens the eyelids and allows the rays of light to enter through the re- fractive media, until they are closed in sleep. It has been said that man is a creature of habit, which becomes to him a second nature, and fromi which it is dif^cult and oftentimes impossible for him to break away. The habit thus acquired, of contraction of the ciliary muscle coincident with the act of vision, is hard to abandon entirely, even after the error of refraction is fully corrected by convex glasses placed before the eyes and all necessity for the use of the ac- commodation thus removed. Hence it follows if there is a correction (either partial or entire) of the hypermetropia by means of the accommodation, and in addition there is a correction of the same defect by means of convex glasses, there is evidently a surplus of correc- IIYPERMETROriA. i.r tion, and the i^lasses appear to be too strong and cannot be worn. In other words, we are able to correct, by the employment of glasses, only that portion of the hypermetropia which the accommodation by its relaxation will permit us to do, or which we can coax the accommodation not to correct, and this brings us back to the point from which we started and which we emphasized in the last issue, that we can scarcely ever give a glass to do more than correct the manifest hypermetropia. lUARRlXG OF IMAGES DUE TO THE SCREEN I'.EIXG TOO CLOSE TO THE REFRACTIVE MEDIUM. In hypermetropia the focus of parallel rays is behind the retina, and hence the rays strike the retina before they have been united in a focal point, the reason being that the retina (or the screen on which the images are formed) is closer to the crystalline lens than the focal distance of the dioptric media of the eye. Any student of optics who is sufficiently interested in these matters, can take a strong convex lens from his trial case and see for himself how the images of objects will be blurred when the screen on which they are formed is closer than the focal distance of the lens. The student will stand in front of a window and hold the lens in such a position that the light coming from the outside will fall upon it and pass through it. A sheet of white paper is to be used for a screen and placed at the focal distance of the lens. If the strength of the latter is 5 D., the sheet of paper will be placed eight inches from it, and small and distinct images of external objects, such as trees and houses, will be formed upon it; every detail of the objects; every leaf and branch of the tree, all the doors and windows of the house, will be clearly defined, and form a beautiful (though dimin- ished and inverted) picture. Tliis illustrates the fomiation of distinct images on the yellow spot of the emmetropic eye. the retina being at the exact focal distance of the dioptric system of the eyes, which may then be said to be ix me/VSURe. If now the screen of white paper be moved slightly, so as to bring it closer to the lens, the sharpness of tlie images is 24 at once (lestroycd; the trees may still be seen in blurred out- lines and the shape of the house be discerned, but none of the fine details can be perceived. If the screen be moved still nearer, the trees will gradually fade out of sight, and even the outlines of the house will be lost. 'Jliis illustrates the fornia- Decembek. 1^6", liimgo as Formed on tlic K( paratus of tiie photographic camera in perfect adjustment, so that the rays proceeding from the title page were accurately focused on the screen. In making the second cut, the screen was moved closer to the condensing lens of the camera, thus stimulating the relative positions of the retina and crystalline lens in the hypermetropic eye. and in this case the rays struck the screen before they were united in a focus, and. as a consequence, the image there formed is imperfect and indistinct. These illustrations have reference to the refractive con- dition of the emmetropic and hypermetropic eyes, that is, with: the eyes in a state of rest and the function of accommodation in a passive condition. The student knows that if the ac- commodation is brought actively into play, the result- ob- tained will be entirely different. The hypermetrope, if the degree of defect be not too high, by the exercise of his accommodative power is able to supple- ment and increase the refractive strength of his eye, and in this way bring the focus of parallel rays forward so as to coin- cide with the retina, and thus counteract the disturl)ing intiu- ence caused by the nearness of the retina to the lens. This would clear up the retinal image and give the hyper- metrope perfect vision, but it would be accomplished only at the expense of a constant strain on the accommodation, which Nature will not sanction, as she expects distant vision to be entirelv devoid of accommodative effort. IIYPERMETROriA. 4\ SUB-DIVISIONS OF HVPERMETROPIA. Manifest hypennetropia has been further divided into- facultative, relative and absolute. We do not attach very nnicli practical vakie to these sub-divisions, but we feel that our readers should not be entirely ignorant of them. Facultative hypermetropia is the term applied to those cases of hypermetropia in which distant objects can be clearly seen, either without or with convex glasses. In these cases the accommodation is suf^ciently strong to overcome the de- fect and afTord perfect vision; and at the same time it is obliging enough, when convex glasses are placed before the eyes, to subside and retire from the field, and allow the convex lenses to do its work. Relative hypermetropia is the term applied to those cases of hypermetropia in which, by the addition of the entire ac- commodative force to the natural refractive condition, the eye still does not possess sufficient power to bring the parallel rays of distant vision, much less the divergent rays of near vision, to a focus on the retina, except by an over-convergence of the visual axes, or, in other words, by squinting. Absolute hypermetropia is the term applied to those cases where distinct vision is impossible without artificial assistance. The entire refractive and accommodative power of the eye, re- inforced by the strongest efTort of convergence, is insufficient to bring parallel rays of light to a focus on the retina, much less the divergent rays proceeding from near objects. Such an eye is entirely dependent upon convex glasses for any vision at ail. The facultative form of hypermetropia is most common in youth, when the accommodation is vigorous and able to overcome the defect. The relative form occurs a little later in life, when the accommodation weakens and no longer suffices to correct the defect without the added assistance of the con- vergence. In old age the accommodation has become entirely exhausted, and then the hypermetropia becomes absolute. From the very nature of it, acquired hypermetropia can never occur in the latent form, but it is always manifest. Neither can it come under the head of facultative, but it maj- ■2S IIYPERMETROI'IA. possibly be relative, although it is more apt to be absolute. All this becomes clear and easily explained when it is remem- "bered that acquired hypermetropia is due to a natural diminu- tion of refraction, and occurs only after the accommodation Tias been shorn of its strength by age, and when all that re- inains of it is memory. Facultative hypermetropia is almost the same as manifest liypermetropia ; although we consider the latter term prefer- able because it is more expressive, the word itself indicating that it is not concealed, but that it is easy of detection, by the .ready acceptance of a convex lens, CAUSES OF HYPERMETROPIA. As has already been shown, the essential condition in liypermetropia is that the retina is too close to the dioptric apparatus, so that the rays of light strike this membrane in •dififusion circles before they have had the opportunity to- unite in a focus. This condftion may be dependent upon several 'dififerent causes, which we will enumerate as follows : 1. -\xial hypermetropia, in which the dioptric system may measure up to the same standard as an emmetropic eye, but the eye is flat and there is a lessening of the antero^posterior diameter of the globe of the eye, and a consequent shortening of its axis. This is by far the most common cause, and it has 'been illustrated in the earlier part of the chapter. The axial form; of hypermetropia is congenital, and is due to an arrest of development of the eye in its growth, particu- larly noticeable in the antero-posterior diameter. Such eyes are distinguished by their smallness and mobility, the diminu- tion in size being oftentimes a noticeable feature. 2. The length or depth of the eye-ball may be the same as an emmetropic eye, but the refractive power of the dioptric apparatus may be too feeble to bring the rays of light to a focus on the retina, which they strike in un-united circles, pro- •ducing the same effect as the axial form. This deficiency of rcfracfiz'C pozver may be due to several •different causes: there may be a depression of the cornea or a lessening of its convexity, as the result of inflammation or •disease; or it may normally be lacking in convexity; there HYPERMETROPIA. 29 may also be a diminution in the natural convexity of the crys- talline lens; and there may also be a reduction in the index of refraction of the refracting media, the aqueous humor, the crystalline lens and the vitreous humor. 3. Aphakia, or the absence of the crystalline lens either naturally or artificially, is a cause of the most pronounced hypermetropia. In such cases there is an absence of all re- fractive power and the eye becomes intensely hypermetropic. AMOUNT OF SHORTENING IN AXIAL HYPERMETROPIA. The following table (after Bonders) shows the amount of shortening of the axis of the eye-ball for the various de- grees of hypermetropia: Degree Diminution of Hypermetropia. of Axial Line. 50 D. .16 p mm. I D. •31 mm. I. 50 D. •47 mm. 2 D. .62 mm. 2. 50 D. •77 mm. 3 D. .92 mm. 3-50 D. 1.06 1 mm. 4 D. 1.22 mm. 4-50 D. 1.4 mm. 5 D. 1.6 mm. 6 D. 1-9 mm. 7 D. 2.2 mm. 8 D. 2.6 mm. 9 D. 2.9 mm. 10 D. 3-2 mm. II D. 3-3 mm. 12 D. 3-4 mm. 13 D. 3-5 mm. 14 D. 3.7 mm. 15 D. 4- mm. 16 D. 4.2 mm. 17 D. 4.4 mm. 18 D. 4.6 mm. 19 D. 4.7 mm. 20 D. 4-9 mm. The axial line of the emmetropic eye is nearly ^;-; of an inch; in 3.50 D. of hypermetropia this would be reduced to ^f of an inch; in 7 D. of hypermetropia to |^, and in 10 D. of hypermetropia to ff of an inch. Tliis shows in the latter grade of the defect a shortening of ^ inch, which is quite a considerable amount. •30 IIVPERMETKOPIA, PRENALIiNXi; OF H VrKKMKTROPIA. llypcrmctropia is the predominant error of refraction. Babies in the majority of cases are bom hypermetropic (per- haps in all cases), althoug-h this condition may afterward de- velop into emmetropia, and finally pass over into myopia. The reason why infants are almost invariably hypermetropic is undoubtedly due to the fact that at birth the eye has scarce reached its full development. \'arious animals, such as frogs, rabbits, cats and dogs, have been examined with the ophthalmoscope to determine their refraction, and all have been found to be hypermetropic, sometimes as much as 3 D. or 4 D. The ciliary muscle in these animals is but poorly developed, the hypermetropia therefore existing in a manifest form; in view- of which their near vision must be ver\' indistinct. This, ho\vever, is a mat- ter of no inconvenience to them, as they are not called upon to use their eyes in near vision for those employments which so nmch tax the human eye, reading, writing and sewing. DEGREE OF HYPERMETROPIA. Ordinarily the degree of hypermetropia may be expressed by the convex lens that is required to correct it. In a.vuil hypermetropia it depends upon the flatness of the eye, or the distance of the retina from the focus of the refracting media. In refractive hypermetropia it depends upon the deficiency of refractive power, or the amount to which this falls below the normal standard. In emmetropia the distance of the retina and the location of the principal focus exactly coincide, and the extent of their departure from each other in hypermetropia would indicate its degree, and the greater this departure the higher the degree of defect. In one case we reckon the distance from the nodal point to the focus of the hypermetropic eye, and the distance from the nodal point to the retina of the same eye. and then compare the two. and the difference between them will denote the hypermetropic deficiencw In the table given we can see the amount of diminution of the axial line for every dioptric of hypermetropia, and IIYPERMKTROI'IA. 31 conversely a certain diniinution in the axial line implies a cer- tain degree of hypernietropia, ami each increases in equal pro- ^xwtion. A convex lens corresponding to the grade of the de- fect will bring forward the focus to the position of the retina, and thus tend to counterbalance the diminution in the axial line. While in refractive hypernietropia, the convex len.s di- rectly supplies the deficiency in refractive power, and at the same time reveals its extent and expresses it in definite terms i»f refraction. A good idea of the difference in shape between the em- metropic eye and the hypermetropic eye may be obtained by ■comparing a round apple with a flat turnip. The round apple represents the normal or emmetrcpic eye. and the turnip the flat or hypermetropic eye, and a comparison of them will con- vey to the mind a well-defined conception of the difference in shape between cmmctropia and hypernietropia. svMPTo^rs of hypermetropia. When a child complains of headache and pain in the eyes, -and is taken from school and charged with stupidity, or pun- ished for idleness, and the family physician advises abstinence from study or change of occupation, and puts the patient through a course of powerful medicines or (puts a course of medicines through him) for an imaginar}- nervous trouble, the intelligent optician will recognize these as symptoms of hyper- metropia; and he knows (and why shouldn't the family physi- cian know?) that medicines are worse than useless in such a case. I)ut that a pair of properly adjusted convex glasses will remove the headache and pain in the eyes (when nothing else can), and will, perhaps, make the child as bright and studious as any of his companions. Otherwise if the cause of the trouble is not recognized and rectified, the child's prospects are blighted for life. The hypermetrope (if the defect is not of too high degree) usually sees well at a distance, but the presence of the defect is made known even in early life, by the pain and symptoms of fatigue that follow any close use of the eyes. By a tension of the accommodation the hypermetrope may be able to read well for awhile, but sooner or later the constant effort to contract 33 llYI'F.RMHTROriA. the muscle of acconiniodation sufficiently for near work causes fatigue and exhaustion of the muscle, and the accommodative effort can be maintained only by the greatest difficulty, and the patient is reminded that he has eyes and that they arc weak and painful ones. The eyes feel strained and painful, the letters run together and become blurred, and there is an instinctive desire to rest the eyes by closing them for a moment or two and compress- ing them. After this a fresh start can be made, only to break down in a little while as before. In short, the symptoms of hypermetropia may be said to consist of pain and discomfort on using the eyes, and an indistinctness of the letters on a printed page. SELF CORRECTION OF HYPERMETROPIA. The condition of every hypermetrope would be a sorry one indeed, if he could not alter and increase the refraction of his eye, and make vision clear and distinct by bringing the focus of rays forward to the retina. While a hypermetrope wdth no inherent power over the defect would see nothing clearly at any distance, fortunately he possesses in his accom- modation a means by which he can increase his refraction and overcome his trouble. While it is possible for distinct vision to be thus purchased by the hypermetrope, it is accomplished only at the expense of a constant strain upon the accommoda- tion, the amount of strain depending on the degree of hyper- metropia. Since hypermetropia can be thus corrected by the indi- vidual himself by the use of his accommodation, no ill effects may be noticed for some time, and indeed the presence of the defect may not even be suspected. At length there comes a time when the accommodation breaks down, and it is no longer equal to long-sustained efforts required by reading and near work. Anything that weakens the accommodation will pre- cipitate this breakdown, hence it is especially liable to show itself after a protracted illness, or if the patient's system has been run down from overwork or anxiety. It also becomes apparent as the patient approaches the presbyopic period of IlvrEKMKTROriA. 33 life, when tlic acconinuulation fails from the natural cliang-es in the eye. The illustratiun previously given, showing the outline of a hypermetropic eye, represents it as refracting parallel rays of light, or those proceeding from a distance of twenty feet or more, in which case the focus is behind the retina and vision is more or less indistinct. As has just been described, this focus is advanced to the retina and vision made clear by the action of the acconunodation, which is thus kept on a constant strain. But when the rays proceed from close objects or from those nearer than twenty feet, they became divergent, and the nearer the object is brought to the eye, the more divergent the rays that proceed from it to enter the eye. Now it does not require much reasoning to show that when divergent rays are refracted by a lens, the resulting focus cannot be at the same place as that of parallel rays, but it will be farther re- moved; or if it is desired to keep the focus at the same place, it is equally evident that more power is necessary in a lens to focus divergent rays at that point than is required to bring ])arallcl rays to a focus at the same distance. THE ACCOMMODATION IN IIYrERMETROPIA. Hence when we apply these principles to the hyper- metropic eye, we find that the focus of divergent rays is back of that of parallel rays, or still further removed from the retina, when the accommodation that is in force for distance remains unchanged. Therefore the accommodation of the hyper- metrope, which must be constantly exerted even for distance, is put to a still greater strain for near vision. As a consequence, it follows in reading, w-riting or sewing, to which the emmetrope comes with fresh and strong eyes, that in the case of the hypermetrope, who is compelled to use some of his accommodation for distant vision, and whose ciliary muscle is in the harness (as it were) from the time the eyes are opened in the morning until they are closed in sleep at night, the start is made with that much of a deficit from the normal strength of the eyes, and near vision is maintained and continued only by calling into action the reserve of accommo- 31 IIYPERMKTKOI'IA. 'Jativc power, and in sonic cases the totality of acconnnoila- tion of wliicli the eye is capable. THE RESERVE MUST NOT I)E IMI'Al KEl). Just as the use of its reserve will impoverish a bank or an insurance company, so the use of its reserve acconnnodativc power will exhaust an eye and cause it to break down; for it must be remembered that a tension of only a portion of the accommodation can be sustained for any length of time. Therefore in the case of the hypermetrope, who is compelled to use a part of his accommodation for distance and the balance oi it for reading, there soon appear pain and fatigue of the eyes and general symptoms of asthenopia, which gradually increase and become so pronounced as to compel a frequent interrup- :ion of the strain on the accommodation by closing the eyes and resting them for a moment or two. The laws of State prohibit the officers of a bank or an insurance company from touching the reserve fund, which must be kept intact, under heavy penalties; but not more so ihan do physical laws forbid any encroachment on the reserve ■of accommodative power, else equally severe punishment may follow. As a rule, banks and insurance companies are so con- servatively managed that not only is the reserve not infringed upon, but, on the other hand, it is from time to time increased, and to that extent is the institution inherently strengthened and raised in public estimation. Rectitude of character, as well as fear of the law, averts any violation of the reserve in banks and insurance companies, except in rare instances, when -.he offender is forced to pay the penalty for his crimes. But no high sense of duty to one's self, nor even the fear of the suffering that is sure to follow^ prevents violation of the laws of health, as is noticeably evidenced on every liand by the abuse of the eyes and of the stomach. The hypermetropic eye is urged to the full extent of its accommodative power, until it breaks dow^n from sheer exhaustion, while the stomach is overloaded at all hours of the day and night with rich and indig-estible food, until it finally rebels and is unable to perform its functions. IIVPERMETROPIA. 35 FAR-SIGHTEDNESS. The popular term for hypermetropia is far-sightedness or long-sig-htcdness, and the use of these words has led the laity to believe that such eyes can see better at a distance than em- metropic eyes; but these terms are misnomers and are mis- leading, because a hypermetropic eye cannot see any better at a distance than an emmetropic eye, and besides, what it does see is only at the expense of an unnatural use of the accom- modation. The student who understands the shape of the hypermetropic eye, and the difficulties under which it labors, will realize that it is far from being as good an eye as the normal. Then, too, it frequently happens that hypermetropia, if of high degree, very much diminishes the acuteness of vision. CONFOUNDED WITH MYOPIA. ->^ On account of this impairment of vision, hypermetropia /► is sometimes mistaken, even by the patient himself, for myopia. ) These are cases of hypermetropia of high degree, in which the person finds that he is able to materially improve his reading vision by holding his book close, which increases the size of the retinal image, intensifies the illumination, and b}' con- tracting the pupil cuts ofif some of the circles of dififusion.. Is it any wonder under these circumstances that the case is looked upon as one of myopia? These matters can perhaps he best emphasized by a few illustrative cases taken from the Avriter's record-book. A CASE OF HYPERMETROPIA SIMULATING MYOPIA. William F. Aged ten years. School-boy. Comes to me with the statement that he has always been near-sighted, and that of late his eyes are getting worse. They hurt when lie reads, and vision is quite indistinct, so much so that he is compelled to almost close his lids in order to see. There is also a convergent squint, which alternates between the two «yes. R. V. = TjVi^, L. \''. = ,"1, „. Reads Jaeger No. 9, 2 in. to 5 in. A histor)' such as this, with so imperfect near and distant vision, is very apt to mislead the average optician into sup- 36 IIYPERMETROPIA. posing that he had a case of myopia to deal with; and really. to any but a skilled refractionist, this would be a most natural error, for is not the boy compelled to hold his book ver)- close to his eyes, and is not his distant vision imperfect and indis- tinct, and does he not half close his eyelids, as all myopes are apt to do? In testing- his eyes with convex lenses, I soon found it was a case of high hypermetropia, but vision was scarcely sat- isfactory even wnth the best glasses I could give him. As this was an unusual case, and as he desired the removal of the strabismus, I instilled atropine in his eyes for a week, during which time I operated on his eye for the correction of the strabismus. I kept him under observation for two weeks, and. then ordered the following glasses: L. J ■-' ' for constant wear. Some three weeks later he reports eyes as comfortable, able to read and study with satisfaction, and does not have to hold book so near, nor half close lids, in reading, as formerly. ANOTHER CASE OF IIYPERMETROPIA, IN WHICH AN OPTICIAN PRESCRIBES CONCAVE GLASSES. Annie F. Aged seventeen years. A sister of the boy iu case above narrated. She comes with nearly the same history as her brother. She says she has always been near-sighted^ but does not have much pain in her eyes unless she uses them for too long a time. Some months ago- she purchased a pair of glasses from an optician (which she showed me, and which I found on examination to be — 3.50 D.), but they have been of no benefit to her and she has used them but little. R, V. = -jV^, L. V. l^-jj. Refraction = manifest hypermetropia of 3.50 D. Reads Jaeger No. 9, 2 in. to 7 in. With + 3.50 D. can read the same print out to 1 1 in. Prescribed for her R ) L,. J • ^'^ ' for constant wear. Two months later she reports that her sight has improved very much, and that she can see better than she ever could, and is now able tO' use her eyes a great deal, without pain or discomfort. IIYPERMETROPIA. 37 THE MORAL OF THESE CASES. One lesson to be learned from the above cases is that too much reliance should not be placed on the patient's statements. Both the boy and the girl called themselves near-sig-hted, and they both accepted concave glasses when placed before their eyes. Under these circumstances nothing is more natural to the unskilled optician than to regard these as cases of myopia, and hence every man should be constantly on his guard to avoid falling into such a grievous error. The reader of these pages, even though he possesses only a moderate amount of knowledge and experience, is aware that to give concave glasses to either of the above cases would not only fail to relieve them, but would make their eyes infinitely worse than to wear no glasses at all, it would, in fact, only be adding fuel to the fire. In the boy's case he came to me at first hand, and I was able to correctly diagnose the trouble and prescribe the proper glasses, and hence he suffered no injury to his eyes from im- proper lenses. But the girl ran a great risk of ruining her eyes with the concave glasses that were prescribed for her, and she escaped only because the glasses were of no benefit and she did not wear them. Another interesting point that impresses us in the study of these cases is the occurrence of two such marked cases of hypermetropia in the same family. ANOTHER CASE OF HYPERMETROPIA SIMULATING MYOPIA. Mary H. Aged fifteen years. About a year ago her eyes commenced to trouble her. She consulted an oculist, who told her it was necessary to drop atropine into her eyes, to which she and her parents objected. She was then taken to another oculist, who said she didn't need any glasses. She comes to me with the statement that she has always held her book close to her eyes, but recently is compelled to hold it closer than ever. Complains of a great deal of head- ache, and of a dull, heavy pain over eyes, which is much worse after readinjr. 38 IIYPERMETROriA. V. = 11 Hm. = + 1.25 D., with which V. = 1§. Reads. Jaeger 3, 2^ in. to 9 in. With the + 1.25 glasses the range of acconiniodation is from 3 in. to 33 in. Ordered R- 1 -!- I 2=; D Iv. j ' ■ ^ 'for constant wear. Three years later she reports that glasses have given the greatest satisfaction in every particular, and she wants them put into a gold frame. One interesting point about this case is the limited range of accommodation for so small a degree of hypermetropia, and the wonderful effect of the glasses in increasing her read- ing limit from nine inches to thirty-three inches. Cases like this are afforded untold benefit from the proper glasses, while at the same time they are a source of great satisfaction to the prescribing optician. The distance of the far point in this case (nine inches) would point toward myopia, although with an acuteness of vision of 5^ but a slight degree would be possible. ANOTHER SIMILAR CASE. ' Mrs. Sarah K. Aged thirty-eight years. Says she has been near-sighted all her life, but has never been able to get glasses to suit her eyes. V. = -sVV- Hm. -f 5.50 D., with which V. = i§. Can read only large size print, and can read no farther off than seven inches. With the 4- 5.50 D. lenses can read out to twelve inches. As these glasses correct only her manifest hypermetropia, and as she is approaching the presbyopic period, she will consequently need a stronger pair for reading. After testing her eyes for reading I ordered R. and L. -|- 8 D., which afforded her the greatest satisfaction. The point of interest in this case is that this woman should have reached thirty-eight years of age without having been able to obtain suitable glasses, which can be explained on oiie of two grounds : Either the optician gave her concave glasses because she said she was near-sighted, which would only hinder her eyes instead of helping them; or he did not know how to properly test her eyes for hypermetropia, and hence gave her only a weak convex glass of not sufficient strength IIYPERMETROPIA. 39 to afford her relief, because he was afraid he niig-ht injure her eyes by giving' her too strong a glass. ANOTHER CASE OF II VPERMETROriA, CLASSED AS ONE OF MYOPIA. Lizzie H. Aged twenty-eight years. Says she has al- ways been near-sighted, and when attending school the teacher allowed her to go close to the windows in order to be able to see to read. On examination I found her vision ig, and with the unassisted eye was unable to read even the largest size print on the reading test card. A pair of -f 8 D. enabled her to read ordinary print with ease and comfort, and gave her good distant vision, A CASE OF IIYPERMETROPIA TREATED WITH CONCAVE GLASSES. Susan G. Aged ten years. Complains of a great deal of pain in eyes, and headache. She showed me a pair of — 4 D. glasses which an optician had given her, but which she had not been able to wear. She cannot see at a distance with them, nor can she read with them; neither can she read without them, as her eyes have gotten into such a weak and irritable condition. An examination showed her vision equals ^^. and a manifest hypermetropia of -j- 1.25 D. Is able to read news- paper print no farther away than nine inches. As the girl was young it seemed best to commence with weak lenses, and hence she was ordered -f .75 D. for constant wear. A week later she returned to have the glasses set in a gold frame, and her report was that they had given the greatest satisfaction ; she can see well with them both far and near, with entire relief from the pain in her head and eyes. The error of the optician in giving this young girl a con- cave lens of 4 D. is a most inexcusable one. It is difficult to understand how such a mistake could have been made by an optician of any intelligence, except on the supposition that it was looked upon as a case of myopia, and the concave glasses were prescribed according to the rule in myopia that the dis- tance of the far point expresses the degree of defect and at the same time the correcting glass. 40 IlYPER^[KTRO^TA. 1 1' the o]>tician had examined her distant vision, he could hardly have made such an error, because a vision of ^^ is not compatible with a myopia of 4 D.; and besides, if he had measured her refraction according- to the methods laid down in The JMaxlat., he would certainly have found some evidence of the existence of hypcrmetropia; at least nothing to lead him to ])rescribe a — 4 D. glass. A grievous error of this kind would permanently injure the eyes if the patient continued to wear the glasses, and when discovered it brings reproach on opticians as a class. A FIXAL CASE OF IIYPERMETROPIA IN WHICH CONCAVE GLASSES WERE PRESCRIBED. r^lRS. K. G. Aged twenty-three years. Had been having trouble with her eyes for some time previously, and about three months ago consulted an optician, who gave her a pair of — I D. glasses. She has tried to wear these glasses, but they cause her eyes to ache, and she is unable to thread a needle ^vilh them. ' ' A careful examination was made with the following result: R. E., vision ^f; with -f- i D. = |f. L. E., vision = If, with a manifest hypermetropia of .75 D. Is able to read Jaeger No. 4 only, 6 in. to 11 in. The above lenses increase the reading far point to sixteen inches. Ordered R. E. + i, L. E. + .75, for constant wear, and these alTorded the greatest comfort and satisfaction. MORAL OF THESE CASES. The wTitcr could give the history of a great many more similar cases from his own case-books, but sufficient have probably been narrated to call attention to. and to emphasize, this most important point, that is. the great danger to the eye when concave glasses are prescribed in cases of hypermetropia. Of course it is a natural error, into which the optician may easily be misled by the patient's statements that he is near- sighted, and by his answers when test lenses are placed before his eyes; but it is to be hoped that no reader of The ^1 wrAf, will ever allow himself to fall into such an error, and he cer- HVrERMETROPIA. 41 -.ainly will not if he carefully follows the directions given in -ihis chapter and in the chapter on Method of Examination. Too much stress cannot be laid on the importance of the oroper differential diagnosis between hypermetropia and myopia, and at the risk of repetition (which, after all, serves as the best means of fixing a fact in the student's mind) we will repeat the rule as follows: In testing the refraction of an -eye ahavys commence icith convex lenses, and if these make vision clearer, or if they are accepted at all, it is prima facie evidence of the existence of hypermetropia; for the diagnosis of hypermetropia, in testing with the trial case, depends upon -.he acceptance of a convex lens for distance, and in such a case concave lenses should not be used, else they too be accepted, -tnd then the optician becomes mixed and the diagnosis is in loubt. For it should be remembered that weak concave u-lasscs are accepted for distance by almost every eye, and rarely fail to cause some slight improvement in vision; and nence if they are tried first and at once accepted, the optician may too hastily jump to the conclusion that the case is one of myopia, and may be led to commit the unpardonable error of prescribing concave glasses in a case of hypermetropia. LATKNT nVPERMETROPIA. The optician will sometimes meet with cases of suspected :iypermetropia that will not accept convex lenses; their vision is ^g. and all convex lenses blur it. In spite of this all the svmptoms may point to hypennetropia, and the optician may oc able to detect its presence by the retinoscope and by other means which will be described later on. Such patients are \mable to relax their long-contracted ciliary muscles in the j-lightest degree; and in these cases the total hypermetropia is all latent. This condition of non-relaxation of the muscle of accommodation is most frequently found in young persons, :n whom it is strong and vigorous. In some cases where -onvex lenses are thus rejected when each eye is tested separately, it may be possible to secure their acceptance by '.rying the eyes together in binocular vision, when the accom- .modation relaxes more readilv. 42 IIVPERMETROriA. THE OrilTIIALMOSCOPE IX IIvrM-.KM ETROl'IA. It has been stated that the hypermetropic eye, when at rest, is adapted for converg-ent rays, and hence when the eye is strongly illuminated, the emergent rays will follow the same course in returning, and as a consequence will diverge from the surface of the cornea. During the ophthalmoscopic ex- amination of the hypermetropic eye by the direct method, the instrument is held very close to the eye under observation, and the optician rotates behind the mirror, and into its aper- ture, a convex lens of sufficient refractive power to render parallel the divergent rays issuing from the patient's eye, when an erect, virtual, ma^iified image of the retina of this eye will' become visible to the observer. The focal power of the con- vex lens necessary to make the divergent rays parallel will represent the degree of the hypermetropia. This method of determining the refraction does not always yield accurate results, and should not be relied upon to the exclusion of the test by trial lenses; but in cases where the answers are unsatisfactory with the trial case, and particularl}^ in children, it suffices to give a very satisfactory clue to the condition of the refraction and the degree of defect. With the improved ophthalmoscopes of the present day, the proper correcting lens can be found by simply rotating the disk until' the strongest convex lens is reached that does not blur the retinal picture. FAR-SIGHTEDXESS. The common term in use among- the lait}- for hyper- metropia is "far-sightedness," in contradistinction to near- sightedness, the common name for myopia. As this term- would indicate, the idea generally prevails that the hyper- metropic eye can see at a greater distance and can see better far off than an emmetropic eye. This is a great mistake; nothing can be better for vision than a normal or emmetropic eye. Instead of being more advantageous, the hypermetropic eye is an undeveloped eye, and because of this incompleteness there is apt to be an insufficiency in the layer of rods and cones of the retina, as well as of the optic nerve fibers, and therefore HYPERMETROriA. 4t> the vision can scarcely measure up to the normal standard of distinctness for distant objects, much less for near ones. COURSE OF IIVPERMETROriA. While myopia inclines to increase in proportion to the close use of the eyes and in consequence thereof, hyper- metropia, on the other hand, rarely increases, but rather tends to decrease. It has been shown that the hypermetropic eye possesses a larger ciliary muscle than the myopic or the em- metropic eye, and that its circular fibers particularly are more highly developed, few or none of which are found in the myopic eye. The statement is also made that the yellow spot is situated farther toward the temporal side than is the case in the emmetropic eye, thus increasing the distance between the disk and the macula. VISION IN HYPERMETROPIA. In the lower grades of hypermetropia during adolescence, vision usually equals |^, and the defect is almost or altogether latent, and is therefore difScult of detection; but in the higher grades of the defect vision is more or less impaired, even wdien the hypermetropia is completely neutralized by the proper convex lenses. This deficiency of sight depends partly on the insufificiency of the rods and cones of the retina as mentioned above, but more perhaps on the nearness of the retina to the nodal point, which causes the size of the retinal images to be smaller than in emmetropic eyes, and being smaller they are able to impress fewer of the perceptive nervous elements. Even when the size of the images is increased by the magnifying effect of convex lenses, the vision is not always raised to normal, which tends to prove the scarcity of the rods and cones. For these reasons persons with a marked degree of hyper- metropia cannot see well at night or in dimly-lighted rooms. Such persons fall into the habit of partially closing their lids, and bringing small objects well illuminated quite close to the eyes, where for a short time they can be seen distinctly. The holding of objects close to the eyes is so contrary to the popu- 44 HYPERMETROPIA. lar ideas about far-sightedness, that an explanation of this phenomenon would not be out of order. As the object ap- proaches the eye the size of the retinal image increases to a much greater extent than the circles of diffusion. The strong illumination which is necessary to enable the objects to be seen causes a contraction of the pupil, which shuts out the circum- ferential rays and diminishes the diffusion circles, in which it is aided by the half-closed lids. At the same time the hyper- metrope leanis to suppress the impressions of any un-united rays that fall upon the retina. In this way these hyper- metropes are sometimes able to do fine work and read small print even without the aid of glasses, a fact that is almost in- credible. Is it any wonder then that these cases are sometimes confounded with myopia? They can, however, see distant objects with convex g-lasses, which would be quite impossible in myopia. Tlie ability to read so close to the eyes requires a very •strong supply of light, not only to illuminate the letters, but also to contract the pupil to its smallest size, which, assisted "by the partially closed lids, acts as a stenopaic apparatus, very much on the same principle as the improvement in vision caused by the pin-hole disk; we consider a single ray as emanating from each point of an object, and passing through the dioptric media and forming an image on the retina. ESTIMATION OF THE TOTAL HYPERMETROPIA. The total hypermetropia can be determined upon by par- alyzing the accommodation by a strong solution of atropine (or one of the other mydriatics) and then selecting the glass that affords the best distant vision. The total hypermetropia as thus ascertained is oftentimes very much greater than the manifest error. The writer has seen many cases where the manifest hypermetropia was less than i D., and some in which there was no evidence even of any manifest defect, where he found the total h3^permetropia, as revealed by the mydriatic, to be 3 D. or 4 D. and even more. HVrERMETROriA. 45 THE USE OF ATROPINE DISCOUNTENANCED. But tlie employment of atropine belong-s largely to the province of the physician or oculist, and we advise against its use by the optician. It produces a most alarming disturb- ance of vision in hypermetropic eyes, which in some cases has so frightened the individual, even where he was advised in advance of its probable effect, that he has refused to submit to a second instillation of the drug, and either tried to get along without glasses or sought them elsewhere. Many persons liave consulted the writer, who have at- tributed (whether justly or unjustly) much of their trouble to the atropine that had been dropped in their eyes, and have declared with the greatest positiveness that their sight has never been as good since the drug was used, as it had been before. In view of the possibility of such an experience, it would scarcely be policy for the optician to run the risk of injuring his reputation in this way. Nor indeed is it really necessar)' in a majority of cases; for even though the total hypermetropia is ascertained by the use of the mydriatic, the patient would be unable to wear glasses strong enough to correct it all. In fact, the custom of the writer is to advise his students to correct only the manifest error, and in almost all cases it will be found that such glasses are about as strong as the patient can wear. This is particu- larly true of young persons, in whom the accommodation is strong and active. As the person grows older, and the ac- commodation lessens and weakens, more and more of the latent defect becomes manifest, and stronger and stronger glasses can be borne and are called for. We repeat the statement that almost any case of hyper- metropia can be corrected without the use of atropine, at least temporarily. Tlie ^^Titer does not employ the dnig nearly so much as he did in the earlier years of his practice. He has frequently found that the glasses that were indicated by the preliminary examination, were the same glasses that were pre- scribed after repeated examinations under atropine, because his experience had taught him that the total error could not all be neutralized; and this experience has occurred so often AG IIVrKRMi:TK01'IA. that he was led to look upon atropine as ahiiost superlluous in the detection and correction of the majority of cases of optical defect, because the result of a careful examination Avithout atropine indicates glasses about as strong as they can be borne even after the use of the drug. While atropine is used and the glasses are prescribed Avhile the eyes are still under its influence, such glasses usually prove to be too strong, so much so as to prohibit their use, because the attempt is made to correct too much of the latent defect. We will cite a case in illustration, in which there is only a slight manifest error, but probably a marked degree of latent defect. Atropine had previously been used by another physician, which developed the latent hypermetropia and the glasses had been prescribed accordingly, with the result, as so often happens, that they could not be worn. CASE OF HYPERMETROPIA CORRECTED UNDER ATROPINE IN WHICH THE GLASSES WERE NOT SATISFACTORY. J. L. B. Aged eighteen years. Always had weak eyes and has suffered a great deal with neuralgia in eyes. About two years ago was given a pair of glasses, which w^ere fitted after repeated examinations under atropine, but they have never been of any benefit to her, and in fact she not been able to W'Car them. Vision of both eyes is j|, and she accepts + .25 C. axis 90°. Reads Jaeger No. 4, 4^ inches to 36 inches. These cylinders were ordered for constant wear; they afforded her the greatest satisfaction and relieved all the unpleasant symptoms of which she complained. There is possibly some latent hypermetropia in this case m connection with the slight hypermetropic astigmatism, but which W'Ould not bear correction, as evidenced by the trouble with the glasses first prescribed. LATENT HYPERMETROPIA VS. MANIFEST. In some cases the hypermetropia may be almost entirely latent, and a casual examination would show very little, if any, ■manifest error. In other cases the hypermetropia may be almost entirely manifest, and an examination under atropine would reveal very little, if any, latent defect. Another point IIVPERMETROPIA. . 47 Avith which the optician should be famiHar, is the fact that the amount of discomfort is not always proportionate to the degree of hypermetropia. These points are well illustrated in the two following- cases, both of whom happened to be under niy care at the same time: A CASE IN WHICH THE HYPERMETROriA IS ALMOST ENTIRELY MANIFEST. Mrs. J. M. H. Aged forty-two years. About eight years ago eyes first commenced to trouble her, but they have been getting worse during the past two or three years. Has had her glasses changed frequently, but to no advantage. Her present glasses, which were given her for reading only, are -f- 1.50 D., besides which she also has a pair of -f 2 D. Com- plains of frequent attacks of neuralgia. Unable to read or sew more than five minutes at a time, when she begins to feel sick and dizzy. V. = ^^ ; Hm. = + 2.50 D., with which V. = -j 5. Can't see to read without glasses; with + 3.50 D. reads Jaeger Xo. 4, 8 to 32 inches. .Under atropine, V. =i5tjV. Ht. = -f 3.50 D. with which Ordered -f 2.50 D. for distance, and -f 4 D.' for reading. These glasses relieved the neuralgia and enabled her to use her eyes with comfort. The optician who fitted this case with -f 2 D. for reading evidently did not or could not test her refraction to determine if she was hypermetropic or if any other error existed He mistook it for a case of early presbyopia, and as she was not very far advanced in years, he was afraid of giving her glasses too strong; they were not sufficient to correct the manifest hypermetropia, much less to enable her to read or sew with any degree of comfort. A CASE IN WHICH THE HYPERMETROPIA IS ALMOST ENTIRELY LATENT. Mrs. Dr. G. A. K. Aged thirty-one years. Has been wearing glasses more or less for reading and sewing for the past eleven years. Her reading glasses are -f 1.50 D., which she uses without much discomfort. Her eves trouble her most 48 IIYrKRMETROriA. when from any cause her system is run down, while ih annoy her but little when she enjoys her usual health. Slvr has no particular difficulty with her eyes at present, but h - luisband, being- a physician, advises her to have her eye; c , amined. V. = If. Hm. = + .75 D. Reads Jaeger No. 3. 11 ::. to 30 in. Under atropine V. = ijVV- Ht. = + 4 D., \vir,b which V. = xF- Ordered + 2.50 D. for reading, but she com- plained that these were too strong, and not entirely comforr.- able in spite of the degree of hypermetropia present, and I wa.^ compelled to reduce them to -!- 1.50 D. for reading, the same number she had been using. As her distant vision was unim- paired, and she had no trouble with her eyes, glasses for con- stant wear seemed unnecessary. THESE CASES COMPARED. A careful study and comparison of these two cases will amply repay the practical optician, and to assist him we will make mention of a few of the important points. In the first place, Mrs. H., with a total hypennetropia of 3.50, sufifers greatly with neuralgia and inability to use her eyes, while Mrs. K., Adth a total error of 4 D., has no pain and uses her eyes with comparative comfort. In the next place, Mrs. H. shows a manifest defect of 2.50 D., while Mrs. K., whose total defect is .50 D. greater than Mrs. H., reveals a manifest error of only .75 D, This ac- counts for the difference in the glasses prescribed for each lady, and explains why Mrs. K. needs no glasses for distance, and why such weak glasses suffice for her for reading. Of course the difference in the age of these patients is the reason for the variance in the symptoms referred to. In the first case the accommodation is weakened by age and is unable to overcome the defect, and in the second case it still retains the vigor of youth and suffices to keep the refractive power of the eye up to the necessary degree. HISTORY OF HYPERMETROPIA. The slighter degrees of hypermetropia occasion but little inconvenience until the individual reaches the thirties, when HYPERMETROPIA. 49 it manifests itself ciiiefly as an early presbyopia. In cases where the defect is a little more marked (from i D. to 3 D.), it usually causes the condition of convergent strabismus. In still higher degrees of hypermetropia, strabismus may be absent, but a group of symptoms known as "asthenopia" ma\- be produced. This is a pen picture of the effects of the several degrees of hypermetropia, varying in different cases according to the peculiarities of each individual (his muscular power and nervous susceptibility), iSometimes a very slight degree of hypermetropia may be the cause of much distress; in other cases a much higher amount of refractive error produces but little discomfort. The asthenopic symptoms of hypermetropia are especially liable to manifest themselves after an illness, or if the health of the patient is impaired from overwork, anxiety or other causes. Distant objects arc seen by the cnnnctropic eye without any effort of accommodation, consequently its whole power is free for use in near vision. But in hypermetropia, on the contrary, there is no distinct vision of any object even at a distance, without more or less effort of acconmiodation. Hence there is a deficiency of acconmiodation to start with, or in other words an extra weight to carry, and as a matter of course under such circumstances the accommodation gives out much sooner than it othenvise would. The less the degree of hypermetropia, all other things being equal, the longer the eyes can be used before the annoying symptoms supervene. Therefore it becomes evident that the length of time the ten- sion of the accommodation can be kept up is to a great extent dependent upon the degree of defect, or the amount of extra weight the ciliary muscle has to carry. In the earlier years the soft and }iel(ling crystalline lens and the strong and well-developed ciliary muscle enable the eyes to do their work without much complaint even in the face of a high degree of hypermetropia. But as years pass on and the lens becomes firmer and the muscles weaker, then the troublesome symptoms manifest themselves and become very aimoying. 50 in ri;K.\ii- iHoiMA i .\ en i i.orkx. 'Ilu- f\c strain that is caused by hypernictropia cannot fail to have an effect upon the character and natural disposi- tion of children, and freciuently tends to render them peevish and fretful, as well as Tlesponding and lacking in self-reliance. The constant effort required for vision retards the quickness of perception and comprehension, and the exhaustion that is sure to follow this continued straining- of the eyes interferes with the concentration of the attention; for these reasons the child unconsciously and without knowing the reason why, acquires a distaste for l)ooks. An hypermetropic boy sits down to study his lessons full of the enthusiasm of youth and with a determination to per- form his task. Sooner or later a feeling of uneasiness creeps over him and makes him restless. He thinks he needs more light and he moves near to the window or close to the lamp. Then the glare of the increased light irritates the eyes, and they begin to feel heavy, and the face becomes flushed. He makes effort after effort to continue his work, but he finds it is of no use; his head droops over the table, and he finally falls asleep. This struggle is repeated day after day, and the naturally bright boy becomes backward and stupid. He gradually loses his desire for study, and he continues through life without the habit of application and the power of concentration, which are so essential to success, and all on account of a neglected optical defect, which should have been corrected at the commence- ment of his education. ])ETKRMIXATIOX OF II VPERMETROPIA. The optician will be able to determine the existence of hypermetropia when any one of the following conditions is found to be present : 1. When distant vision is improved by a convex lens, or when the acuteness of vision equals |;; and is just as good with a convex lens as without. 2. When a patient is able to read fine print through a convex glass at a greater distance than the focal length of the lens. ve V off HVl'ERMETROPIA. 51 3, When the near point hes at a greater distance from the eye than is proper for the age, or when the amphtude of accommodatioii falls below the normal standard. A refer- ence to the tables in the Chapter on Presbyopia will show the distance of the near point and the amount of amplitude of accommodation at the various ages, a departure from which can be readily detected. 4. When with the ophthalmoscope the fundus of the ey can be distinctly seen with a convex lens in the aperture the instrument. ^ The presence of any or all of these conditions indicates / The existence of hypermetropia, which is then to be measured rind corrected by the means to be described. AMOUNT OF HVrERMETROPIA. The amount of hypermetropia may vary from a fraction of a dioptric to fifteen dioptrics; when it exceeds 6 D. it is looked upon as a case of high hypermetropia. W'hen the defect is under 4 D. in young persons with a good accom- modation, the acuteness of vision as a rule is normal and equals |y. Such patients may accept weak convex lenses, but without any improvement in vision, which has not fallen below^ the normal standard, the defect existing in the latent form. When the degree of hypermetropia is greater than 4 D., the vision is apt to be more or less impaired, which in moderate degrees is raised to normal by the proper convex lenses. In extreme cases of high hypermetropia it is impos- sible to secure normal vision by the most carefully adjusted glasses. SIGNS OF HYPERMETROPIA. The presence of hypermetropia makes it a matter of more or less difficulty to maintain distinct vision of small objects for any great length of time. The vision begins to blur and the patient is compelled to stop reading and rub his eyes. This for the moment seems to clear up the vision, and the lxx)k is again taken up and a fresh start is made; but the blurring occurs again and again until finally the accommoda- tion becomes entirely exhausted, and the reading must be discontinued. 52 lIVrERMETROriA. The book is often held in a very strong Hght, which serves to contract the pupil and thus render vision clearer. At the same time many hypermetropic persons fall into the habit of holding the book quite close to their eyes, thus increasing the size of the visual angle, when vision is also assisted by the half-closed lids acting as a stenopaic apparatus. PAIN IN HYPERMETROPIA, One of the principal subjective symptoms of which the hypermetropic patient complains is pain, which varies very much as to its character and location. Sometimes it is in the eye-ball, sometimes over the brow and through the temple, sometimes on the top of the head, sometimes in the back of the head and nape of the neck, and in extreme cases the pain may be accompanied by nausea and vomiting. Headache is a very common symptom, and is often described under the French term migraine. TESTING HYPERMETROPIA. If the symptoms have indicated the existence of hyper- metropia, and the preliminary examination has confirmed this. the eyes must then be carefully tested to determine the degree of defect. Each eye should be tested separately, noting first its visual acuteness, and then commencing the test with weak convex lenses. If a mild convex glass is accepted, the diagnosis of hyper- metropia is assured, and then stronger and stronger glasses are placed before the eye in rapid succession, until the strongest convex lens is reached with which the patient is able to read |^ ; or if it is impossible to raise the acuteness of vision to normal, then the strongest convex lens that affords the best sight in looking at the card hanging twenty feet away. Tliis is the measure of the manifest hypermeiropia. If the acuity of vision is not raised to normal by a convex spherical lens, there is a possibility of the existence of an astigmatic element in the case, for which a careful ex- amination should be made. If, however, vision equals |^ with the spherical lens, it is hardly likely that any astig- matism is present, but still every case should be tested with IIYPERMETROPIxV. 53 a view of its detection if it exists. If none is present, the con- vex lens is all that is necessary to correct the ametropia. In order to insure accuracy, this examination should be repeated two or three times on as many different days. In cases where vision is found to be exactly alike in the two eyes, and if spasm of the accommodation is suspected, the two eyes may be tested together, when more suitable glasses can oftentimes be obtained in this way by the accept- ance of stronger glasses, than when one eye is excluded from the act of vision, because with parallel axes the accommoda- tion is more apt to relax. THE METHOD BY OVER-CORRECTIOX. In cases where the hypermetropia exists largely in a latent form, and where there is consequently difficulty in having the patient accept convex lenses, the following "method by over- correction" will often yield satisfactory results. Place in the trial frame a stronger convex lens than is re- quired, that is, one strong enough to greatly over-correct the defect. This, of course, blurs the vision, but at the same time it encourages the accommodation tO' relax, as the more the relaxation of the accommodation the greater the improve- ment in vision. Then place in the trial frame, in front ot this convex lens, a weak concave lens, which at once causes an improvement in vision. Then try successively stronger and stronger concave lenses until the' zvcakcst one is found that affords a vision of ^g, and then the difference between the two lenses will be the measure of the manifest hypermetropia. F'or instance, a -|- 6 D. lens is placed in the trial frame, Mith which perhaps vision is only equal to ^%%. Concave lenses improve this vision, and it is found a — 4 D. enables the patient to read |§, in which case -f 2 D. is the measure •of the manifest hypermetropia. LATENT HYPERMETROPIA BECOMES MANIFEST. As age advances and the vigor of accommodation lessens, If there is any latent hypermetropia it gradually becomes manifest. A person may have 6 D. of latent hypermetropia at 54 IIYrF-RMHTKOl'IA. ten years of age, when the defect is (Hfficult of detection, or perhaps its existence may not even he suspected. At thirty- five years of age half of it (3 D.) may have become manifest and is easily discovered by the usual tests, and after middle age the whole of it becomes manifest and complicates and augments the natural condition of presbyopia, and then the total hypermetropia and the manifest hypcrmctropia are synonymous terms. A IIVrERMETROPlC EYE CIIANGIXG ITS REFRACTION. The normal condition of refraction in childhood is one of hypermetropia, as has been stated; some persons retain this condition all through life, a considerable number become em- metropic as they grow older, while a certain percentage pass- over into a condition of myopia. In all these changes, from hypermetropia to emmetropia and from emmetropia to myopia, there is a gradual lengthening in the antero-posterior diameter of the eye-ball, and the rapidity of the changes and the degree of myopia finally attained will depend on the amount of lengthening and the recession of the retina from the focus of the parallel rays. When these changes occur they usually take place before adult age is reached. In childhood and youth the membranes and tissues of the eye are soft and yielding, and can offer but little resistance to the causes that tend to elongate the ball. After twenty years of age the tunics of the eye, and especially the sclerotic, become tough and firm, after which there is little danger of these morbid changes taking place, or if they have already commenced, their progress is now checked. SPASM OF ACCOM.MODATIOX. On account of the persistent contraction of the ciliary muscle which is necessary to overcome the error of refraction and render vision distinct, hypermetropia often gives rise to a condition which has been termed spasm of the accommodation. This simulates myopia in all of its symptoms, the resemblance being- particularly noticeable in the impairment of distant vision and the confirmed habit of holding the book close to the eyes. In these cases concave lenses are often accepted IIVPEKMKTKOPJA. ■):> and may cause a great inipravenK'nt in distant vision ; but it need hardly be said that no well-informed optician would order them, as they would only aggravate the trouble and impose a greater strain on the accommodation. This state of spasm is apt to occur in persons whose ner\ - ous system is in a low state of vitality, and, strange to say, ii seems to bear no relation to the vigor of the accommodation. It is almost incredible that persons W'ith a weak accommoda- tion should sufifer with constant contraction of the ciliary mus- cle; but such is really the case. It might be well to remark in passing that spasm of accommodation ma\' occur in crm- ditions of refraction other than hypermetropia. TRK.\TMi:X'r OF IIYPKK.METKOPIA. ]n absolute hypermetr(.)pia vision is indistinct at all dis- tances. The accommodation is not equal to the task of unit- ing even parallel rays (those from a distance) in a focus oti the retina, much less divergent rays (those from near objects). In such cases the rays must be rendered convergent beforc they enter the eye; and this changing of parallel and diverging rays into a convergent form is accomplished by means of con- vex lenses. The treatment, then, of hypermetropia consists in the application of a convex lens of such strength as will impart to parallel rays sufificient convergence to make them focus upon the retina without any effort of the acconmiodation. Diagram of a passive liyperinetr<^)lc eye, the focus of parallel rays lying behind the retina, as shown by the dotted lines. A eonvex lens plneed in front of the eye converges the vays to a focus on the retina, as shown by the plain lines, the accomnio datlon all the whil" bfiiiR qiiioscMit. ^>C) lIVPKRMKTkOriA. TWO PAIRS OF GLASSES MAY BE REQUIRED. ]n many cases two pairs of glasses may be required: one pair to enable distant objects to be distinctly seen, and another pair to permit of fine print being easily read at the ordinary reading distance. Two pairs of glasses become a necessity under one of two conditions: in high degrees of hyperme- tropia and in hypermetropia complicated with presbyopia. When the range of accommodation is much diminished, this deficiency may be compensated for by a change in the position of the glasses. If very strong convex glasses are worn, a slight alteration in their distance from the eyes is equivalent to a change for those of a greater or lesser power, as may be needed to make objects distinctly seen at diflferent distances, thus supplementing the use of the accommodation and obviating the necessity for glasses of an intermediate focus. Therefore great care should be taken to see that such glasses are properly adjusted and centered. As these glasses are usually required for near vision, where a marked converg- ence of the visual axes is called for, the centers of the lenses should be slightly approximated, so that the visual lines may pass through them. If this precaution be overlooked and the rays of light pass through the peripheral portions of the lenses, their prismatic effect is called into play, which may cause a disturbance of the close relation which should exist between the functions of accommodation and convergence, and this may be followed by a train of symptoms making up the con- dition of asthenopia. In facultative hypermetropia where both near and distant vision is good, and the use of the accommodation can be continued without fatigue almost as long as may be desired, no glasses are necessary until the near point has receded be- yond eight or nine inches. This occurs much earlier than in the normal eye, and such persons are required to wear glasses for close work in many cases when only twenty-five or thirty years old. AN UNNATURAL USE OF THE ACCOMMODATIOX. In hypermetropia, as has already been shown, either on account of the faultv formation of the eve-ball or of a de- HYPERMETROPIA. 57 iiciency of refractive and accommodative power, an excessive iimount of muscular power is required to adjust the dioptric ^iipparatus of the eye for near vision. Now, the placing of a •convex lens before such an eye does away with the necessity for a certain amount of muscular effort, and, therefore, the lens represents, or is equivalent to, the expenditure of a cer- tain amount of muscular force. In other words, the convex ]ens lifts a load from the shoulders of the overburdened mus- cle, which is then called upon to perform only its legitimate Avork. In hypermetropia the brain abhors the circles of diffusion that would naturally be formed on the retina and the blurred vision that would result therefrom, and instinctively turns to the function of accommodation and appeals to it to bring the focus of rays forward to the retina and thus restore clearness of vision. In giving the hint to the nerve centers that control the accommodation as to what is expected of it, and while notify- ing- it when the time arrives for action, the brain despatches sufficient nerve force (no more and no less) to the ciliary muscle to accomplish the purpose of clear vision. The most Avonderful thing about this w'hole matter is the accuracy with Avhich the brain measures the work that is to be accomplished, •and the nicety with which it sends forth just the amount of force required. This is an unjust use to which the accommodation is put, Imt it must be continued until the necessary glasses are sup- plied. Transgression on any of Nature's laws is sure to be followed by punishment sooner or later, and the breaking of this law proves no exception to the rule, as is shown by the j torture w^hich some of these hypermetropic and asthenopic y' patients are compelled to sufTer. WHAT GLASSES TO PRESCRIBE. In the correction of hypermetropia by convex lenses in the light of the above statements, the important question naturally arises as to what shall be the power of the glass re- quired in each individual case? This brings up the subject ■'>f the total amoinit of error, and what proportitm of the latent 58 lIVrKKMKTRorjA. portion it is advisable to attempt to correct. Tlie total hyper- nietropia is made up of the sum of the manifest and the latent^ the divisions between which are plainly marked. The former can be easily measured, but the latter can be detected only by the employment of atropine, the use of whichi by the optician has been discountenanced on these pages on every occasion. But, for the sake of argument, suppose the drug had been used and the total error determined in this way. Theoretically it would seem to be the proper thing to at once and completely neutralize it, but practically such glasses are found to be much too strong. Previously there had been an excessive and imnaturai contraction of the ciliary muscle, by means of which a por- tion of the defect had been rendered latent. When the total neutralizing glasses are placed before the eyes, the muscle should completely relax and allow the defect, which it had rendered latent, to now become manifest and correctible by glasses; but instead of this, the contraction of the muscle still continues, which, with the action of the convex lens, supplies an excess of refractive power, which may result in an aggrava- tion of the very symptoms it was intended to relieve. Hence the rule has been formulated not to attempt to correct the total amount of hypermetropia at the first fitting of glasses. CORRECTION OF TOTAL HYrERMETROriA. When a hypermetropic eye is under the influence of atropine, vision at all distances is blurred and indistinct. Tlie full correction of the defect is necessary to clear up distant vision, and a lens 4 D. or 5 D. stronger will enable the patient to see at reading distance. As soon as the effects of the drug have worn off (which may not be for a week) and the accom- modation is again allowed to exercise its function, then dis- tant vision is dimmed when the same glasses are placed before the eyes, and this haziness, which envelopes all distant objects,, continues until the glasses are taken ofif. The tension of the accommodation, which is the disturbing feature in this prob- lem, is a variable quantity in different individuals, some few persons bearing almost or quite the full correction with little HYPERMETROPIA. 5?* discomfort, while a great many otlicrs will tolerate but a small part of the correction. Oculists who are accustomed to employ atropine in the correction of hypermetropia, use different methods in dealing with this difficulty. Sometimes the full correction is ordered and placed before the eyes while still under the influence of the mydriatic, and the patient is instructed to wear them con- stantly all the while that the influence of the drug is wearing off and the accommodation is returning to its normal state. In this way it is hoped to coax the eyes to accept the glasses. It might be well at this point to remind the optician that when the glasses are fitted at fifteen feet (and even at twent\" feet), there is really an over-correction of about .25 D.. because the rays proceeding from these distances are not strictly parallel, and hence the lens that is required to focus them per- fectly on the retina is a little too strong to exactly focus parallel rays. Therefore, even when it is desired to order a full correction, the glass which affords the best vision under atropine at fifteen or twenty feet should be weakened by .25 D. This is a slight step in the direction of enabling patients to wear a full correction. THE FULL CORRECTION' ^L\V NEED TO BE REDUCED. In Other cases the oculist may employ a different mctho' them on, when it found to its amazement that it could read with comfort, and the print seemed large and plain. Ol" course, as soon as it was discovered in this presumptuous use of the old spectacles, the latter were taken away and the child warned never to touch them again under penalty of losing its sight and becoming blind. While the parents acted entirely for the best interests of the child according to their own limited knowledge, yet to us of this day, w-ho are so familiar with the symptoms of hypermetropia and its method of correction by convex glasses, this deprivation of the child of the only means of relief seems little short of barbarous. In former years many ambitious young men, with a fond- ness for study and high hopes for professional distinction, have had their anticipations nipped in tlic 1)U(1 l:)y increasing HVPKRMETROl'IA. ()5 difficulties cxpcricnccil in conliiuiccl near vision, and have been advised not to wear glasses, but to abandon all their chosen plans and go to the country and seek some occupation that does not call for any close use of the eyes. Could any dis- appointment be greater? There are many pupils attending scIkjoI at the present time who cannot use their eyes in study without pain and headache and irritation of the eyes, especially noticeable when they are used by artificial light, due to a hypermetropia, the correction of which by properly adjusted convex glasses would cause these annoying symptoms to vanish as rapidly as the morning dew before the rising sun. Tlie frequency with which these cases are met with by parents and educators em- phasizes the importance of an early recognition of the cause, in order that it may be removed before permanent injury is done to the sight, and that the complaints of children and their apparent stupidity may receive due allowance, and not be met with undeserved punishment. I'ormerly there existed a great prejudice against the wear- ing of convex glasses by children, which doomed them to a continuance of suffering and handicapped them in the acquire- ment of an education. The prevailing idea was that convex lenses were suitable only for aged persons and that children were debarred from their use. A TVnCAL CASE OF HVPERMETKOPIA. In order to point the moral for the preceding remarks, we will relate the history of a typical case, which was originally reported by Dr. Fenner. A young man of sixteen years comes for advice, with the statement that his eyes are weak; they are small, prominent, and set widely apart, and present no external appearance of disease. The pupils act quickly and freely to the stimulus of light. On inquiring into the family history it is learned that he has a brother who suffers like himself, but to a less degree, a sister who has convergent strabismus, and his father was compelled to wear glasses at the age of thirty. The patient's health is good; he attends school and is in- clined to be studious, but, after reading or writing for a short 66 HVIM-RMETROI'IA. time, his eyes grow tired and the letters become indistinct. He moves the book further from his eyes, which enables him to see better for a little while, but soon the letters begin to blur again ; another change in the position of the book affords a temporary improvement, which, however, is soon lost, and any further changes are futile. The eyes become more and more fatigued, there is a slight watering- accompanied by a sensation of smarting and supra-orbital pain, the print pales and the borders and angles of the letters widen out so that they appear as confused, irregular spots on the paper, and he is compelled to discontinue his reading. He closes his eyes, rubs and presses the lids with his fingers for a few moments, when he is able to look around and see distant objects dis- tinctly. After a few minutes of rest in this way he is again able to take up the book and see the letters with their original clearness, but the eyes give out sooner than before, and he goes through the same process of closing his eyes and com- pressing the lids. The pain over his eyes increases and de- velops into a severe headache, the conjunctiva becomes blood- shot, and if he persists in reading he becomes nauseated. Thus he worries along through the day, and if he attempts to study at night all the symptoms are intensified, because his eyes are sensitive to strong artificial light, which produces a painful dazzling and causes a sensation of scratching and roughness as if sand was under the lids. When he awakes in the morning he finds his eye-lids somewhat adherent, but after washing his face and bathing his eyes, he feels all right again, and starts in with his studies with all the vim and enthusiasm of an ambitious youth; soon the well-known symptoms return and he goes through the experience of the previous day. A Sunday's rest invigorates his eyes, and on Monday he has less trouble than on any other day, and during a vacation he experiences no difficulty whatever. He says he has been under the treatment of a physician, who told him he had an "afifection of the optic nerve," gave him medicines, blistered his temples, and dropped "eye-water" into his eyes. On examination his vision is found to equal 1^. Con- vex lenses were tried, conmiencing with -f .50 D., and increas- HVPKRMETROI'IA. 07 ing to + 1.75 D., which were the strongest accepted; -r 2 D. blurred the letters. Hence, his manifest hypermetropia is + 1.75 D. His reading vision is now tried and his amplitude of accommodation measured. He is able to bring the print as close as six inches, but says it requires an appreciable effort; he gradually moves the book farther away as he reads, and by the time he has finished the paragraph it is out as far as fourteen inches. His near point of six inches represents an amplitude of accommodation of 6.50 D., and, as the normal amplitude at this age is ii D., there is presumptive evidence of the existence of 4.50 D. of hypermetropia, and, as the mani- fest error was 1.75 D., the balance exists as latent hyper- metropia. Glasses of + 2 D. are ordered for him, and he remarks, "Why, doctor, you don't want me to wear spectacles, do you?" "Certainly," the oculist answ^ers, "or at least I wish you to try them." He then said, "I used to wear my grandmother's spectacles at night to get my lessons and I could see as well as ever, but when I told our doctor he said I must not use any more, for they would ruin my eyes and make me blind." Notwithstanding his doctor's advice he takes the glasses, re- turns to school, and has no further trouble with his eyes. While ignorance of these matters might be excused in the laity, it is reprehensible in a physician; but now, since the nature of the defect and the proper means of correcting it are well understood, it is hoped, by the diffusion of knowledge, to overcome the prejudice which has so widely existed in the public mind against the wearing of convex glasses by children. TWO IWIRS OF GLASSES. In the higher degrees of hypermetropia. and in hyperme- tropia of persons approaching the presbyopic period of life, two pairs of glasses are required — one pair for distant vision, and the other pair to enable fine print to be easily read at the customary distance. PROPER FITTING OF GLASSES. It should l)c remembered that when strong convex glasses are worn, the removal of the lenses a little farther from the 68 HVl'KKMKTROI'IA. eyes increases their i)o\ver and makes them ecjuivalent to glasses of a liioher number; and, as this is sometimes not desirable, it would not be out of place for the optician to in- struct his patient just how they should be worn. Another point that should not be overlooked in the fitting of such glasses is to see that they are close enough together that the patient looks through the centers of the lenses when converging his eyes for near work, as otherwise, if the line of vision was through the edges of the lenses, the rays of light would be refracted as by prisms with curved surfaces; and, while this might not be undesirable in selected cases, unless it is specially indicated, and particularly if the decentering is outward, it might destroy the harmony betw'een the functions of accommodation and convergence and be productive of asthenopic symptoms. THE PROPER GLASSES. It has been stated on a previous page that the hyperme- tropic eye is unable to see any object distinctly, not even the most remote, without an elTort of accommodation, and the closer the object the more the strain. Consequently, in hyper- metropic eyes the accommodation is in a state of constant tension. When convex glasses are placed before the hypermetropic eye it is found that the ciliary muscle, which has been in a state of contraction for so long a time, cannot wholly relax; there still remains a certain amount of involuntary contrac- tion of the muscle, but this is an element that cannot be meas- ured (except by atropine, which is out of the question), and varies in different individuals. Hence, in fitting such eyes with convex lenses, the strongest they will bear without blurring distant vision is just equal to the amount of relaxation of the muscle of accommo- dation, and this is known as the manifest hypermetropia. The degree of involuntary contraction of the muscle that remains, is the measure of the latent hypermetropia, with vvhich the optician need not concern himself, as he will have done his whole duty in correcting the manifest error. Sometimes there is no manifest hypermetropia, it is all HVPERMETROPIA. G'.> latent, which is particularly the case in younp: persons. At about twenty years of age some of it becomes manifest, the proportion of which increases with advancing years, the latent decreasing in the same ratio, until, finally, in middle life it has entirely disappeared, and all of the hypermctropia is then manifest. A CASE OF MANIFEST II YPERMETROPIA IN WHICH THE LATENT PORTION IS REVEALED BY THE DIMISHED AMPLITUDE OF ACCOMMODATION. Joseph F. Aged twenty-one years. Has no trouble in using his eyes in daytime, but com- plains of inability to read at night. He went to an optician, who gave him a pair of + .50 D. glasses, but they have not been of much benefit to him. On examination his vision is found to equal \^ and a manifest hypermctropia of .50 D. A test of his reading vision showed a range of accommodation of eight inches to thirty-three inches. A near point of eight inches indicates an amplitude of accommodation of only 5 D., whereas the normal amplitude of a person at this age is at least 9.50 D., and hence we are justified in assuming the existence of 4.50 D. of total hyper- mctropia ; and as the test showed only .50 I), of manifest error, there remains 4 D. of latent defect. It was not deemed advis- able to correct the total error, and hence his reading vision was tested with the following results: With 1 D., range of accommodation 7 in. to 33 in. 1501)., .5J4 " :?;? " •J II., .") " 32 " + 2 D. glasses were ordered for reading, and gave the most perfect satisfaction. A CASE OF SLIGHT MANIFEST AND MARKED LATENT HVPERMETROPIA. Mrs. S. M. R. Aged thirty-eight years. Eyes have been failing for the past year. Has constant headache and a great deal of pain and smarting in eyes. Com- plains that she can't see to thread a needle. \'ision ~ y|. Manifest Hy. = .50 D. The near point has receded to sixteen inches, which implies an amplitude of accommodation of 70 HYI'EKMHTROPIA. J. 50 1)., ami. as the normal amplitude at this age is about 5 D., we liave evidence of 2.50 D. of hypernietropia. It is a curious coincidence that if we calculate the reading- glasses according- to the rules given under Presbyopia the same result is obtained. Subtract the glass representing the receded near point (16 in. — 2.50 D.) from the glass repre- senting the point which we wish to make the near point (8 in. = 5 D.), which leaves + 2.50 D. as the glass required. One would expect at this age that more of the latent por- tion would become manifest, and that it has not indicates an exceptionally vigorous condition of the accommodation. Glasses of + 2.50 D. were ordered for reading, and for dis- tance + .75 D. will answer at present, although stronger ones will soon be needed, as the latent trouble becomes manifest. A CASE OF IIVPER.METROPIA IN WHICH READING GLASSES FAILED TO GIVE SATISFACTION UNTIL DISTANCE GLASSES WERE WORN. Mrs. J. H. S. Aged fifty-nine years. Her eyes have been troubling her for past fifteen years, and she has great difficulty in getting glasses to suit. Has been compelled to change glasses frequently, those for reading at present being + 4 D., with which she can see fairly well, but in spite of this they do not give her satisfaction. Vision = I5. With -r 1.50 D. - j|. Ordered + 1.50 D. for dis- tance and constant wear, and advised her to continue the -|- 4 D. glasses for reading. In this case the uncorrected hypermetropia kept the eyes on a constant strain, and consequently when the patient de- sired to read she commenced the task wdth eyes already fatigued, and, therefore, her reading glasses did not seem suit- able, even though they were accurately adjusted for their pur- pose. But, now that her reading glasses are supplemented by distance ones, the constant strain will be relieved, and when she begins to read her eyes will be fresh and the reading .glasses prove all that can be desired. There has been a marked change of late years in the atti- tude of the public in regard to the wearing of convex glasses, and when their use is imperatively demanded for the rectifica- HYl'HRMKTROPIA. 71 tion of some optical defect, there is at least no stubborn protest ; but there is still room for improvement, and instead of this placid acquiescence in their employment we would like to see such a sentiment prevail as would recognize their worth and demand their use wherever and whenever indicatcfl. cAKi'. IN Till': u i.AKixc OF ( ;i,Assi:s. When glasses are i)rcscribed ft^r the correction of hyper- metropia. whether for constant wear or only for readinj^, the optician should give his patient definite instructions that he wear them always for the purpose for which they are given. If they are laid aside at intervals, a return of the old symptoms is apt to follow, and in this way little progress can be made in relieving the eyes and freeing them from irritation. Whereas, if the glasses are worn persistently, comfort is at once experi- enced and the eyes become better and stronger, so much so, in some cases, that the glasses may be dispensed with for general wear and used only for reading. In young persons, whose eyes are strong enough to easily overcome the hypermetropia, whose distant vision is good, and who experience no trouble except in reading, the glasses may be given with the distinct understanding that they need be worn only for close use. As the patient grows toward the presbyopic period of life, these glasses will need to be ex- changed for those of a higher power, and then the old pair will sufificc for distant vision and should be used for that purpose. In the case of intelligent persons who are desirous to be properly fitted the use of the trial case is the decisive method, and the test that is suflficiently trustworthy is the patient's own statement that such or such a lens does not blur the sight, or makes vision clearest, or feels the most comfortable to his eyes. But in the case of stupid persons, or of children, where definite answers can only be obtained with the greatest diffi- culty, or where it is desired to verify the statements made, the optician should have recourse to his ophthalmoscope and retinoscope. the latter especially affording an inexpensive and satisfactory methcnl of determining the state of the refraction. Even with the assistance afforded bv these additional methods, 72 IIVPKR.MRTROl'IA. some cases will still he obscure, and the optician nuist fall hack on his own exiK^rience and he g^uided by general principles, ahvays endeavoring- to press the patient to the most satisfac- tory answers oljtainahle. There is no limit of age as regards the wearing of convex glasses for hypermetropia (or in using the ]>roper glasses for the correction of any other ojnical defect). They may be placed before the eyes of a child as soon as he is old enough to understand that they are not playthings, that being about the age when the child commences to go to schooJ. In those cases of hypermetropia which tend to produce squint, the per- sistent wearing of convex glasses will usually prevent this tendency from being developed. For the same reasons, they should be worn after an operation for strabismus, as a pre- ventive of a return of the defect. THE PrXCTl'M KE.MOTL'M IX II Vl'ERM KTROl'I.V. The emmetropic eye, when at rest, has been shown to be adapted for parallel rays, or those ]iroceeding from infinite distance, consequently its punctum remotum is said to lie at infinity. The hypermetropic eye, on the other hand, is adapted only for convergent rays; but there are no convergent rays in nature, and consequently such an eye is adjusted for a condition that does not exist. The focus of parallel rays lies behind the retina, and the punctum remotum becomes a negative quantity in hypermetropia. The position of this negative point can be found by (or, in other words, the distance of the punctum remotum behind the eye will be equal to) the focus of the convex lens wdiich is required to correct the hypermetropia. The writer finds that this subject is not clearly comprehended by the optical student, and a glance at the various standard text-books shows such conflicting and ambiguous statements that there is no wonder the reader is puzzled and confused and unable to gather a proper understancHng of it. And as it is a matter of consider- able theoretical importance, we will endeavor to describe it so clearly that the beginner of the study cannot fail to understand. HYPERMETROPIA. This illustration shows the punctuni reniotuni oi the hypermetropic eye and the lenses that give to parallel rays sufficient converg-ence to meet upon its retina. The location of the far point behind the eye is the spot to which rays must converge before entering the eye, in order that they may be focused upon the retina. From this state- ment v^e are enabled to formulate the following corollary: The hypermetropic eye, when its accommodation is at rest and its refractive power at a minimum, is adjusted for rays con- verging to its far point, and such converging rays exactly meet upon its retina. The focus of a convex lens is at a certain definite distance f nerve force, and there is no cause for irritation. Hut hypermetropia, by over- taxing the ciliary muscle and destroying the normal relation that should exist between accommodation and convergence, calls for an excessive sup])ly of nervous energy and acts as an irritant to the central nervous system, with the final result of a breakdown and prostration of this im])ortant system, which not onlv causes misery and suffering, but statistics are not wanting to ])rove that the duration of life is materially shortened thereby. Chorea. The cHnical experience of hospital physicians has demonstrated most positively that there is a direct relation- ship between hypermetropia and chorea or St. \'itus's dance; the percentage of this defect in choreic cases being- placed as high as seventy per cent. Therefore it follows that such cases are rapidly cured by eye treatment alone, the correcting glasses stopping a leakage of nervous force that may have been going on for years. Ef>ilc(^sy is one of the most terrible diseases that can befall any human being, and its treatment by drug^s alone is very unsatisfactory. ( )f late years specialists on nervous diseases have found that errors of refraction, and especially hyperme- tropia. bear a direct casual relation to the attacks, and that properly adjusted g-lasses are an indispensable ay the acceptance or rejection of convex lenses for distant vision. A weak convex lens (usually + .50 D) is placed before the eye, the effect of which at once becomes apparent, one way or the other. If the acuteness of vision is fg, and this convex lens blurs it, it is fair to presume that the eye is emmetropic: but if the convex lens is accepted, that is, if the vision remains just as good with the lens as without it, and if the No. 20 line can be just as clearly read, the case is proven to be one of hyperme- tropia. But the test does not end here, as the refraction has only been shown to be hypermetropic, the degree of which may be much greater than that represented by the -r .50 D. lens. A + .75 D. lens is next placed in the trial frame, with which the No. 20 line is still clearly seen. But still the op- tician must not be satisfied, and he proceeds to use the next stronger and another stronger, continuing as long as the patient's vision remains |5, and the letters on this line are dis- tinctly visible. Finally a lens is reached that causes the patient to shake his head and say the letters are not quite as plain as they were before. He may be able to name them, because he has prob- ably learned them by heart by this time, but he is conscious of the fact that their sharpness of outline is less marked, and some of the letters he is doubtful of. What has been determined now? The amount of the manifest hypermetrt^pia has been 90 llVPKKMKTKdlMA. moasiircd, l)y jilaoiiii;' sironiior and stroiii^-or convex lenses in front of the eye imtil the vision was made worse. In other words, the refraction of the eye was increased more and more by the addition of the convex lenses, until at last the focus of rays of light was formed in the vitreous humor in front of the retina, whicli sinudated a condition of niy<)])ia, and distant \ision was corresjjondingly impaired. Jn that class of cases where the vision falls below f^, the test is commenced with convex lenses, w'hich are not only accepted, but cause a marked improvement in vision. A + .50 D. lens is tried first, and at once the patient notices that the letters are clearer and blacker, and perhaps he is enabled to read a few letters on the next line below. Then a -f .75 lens is tried, and a + 1 D.. with a noticeable improvement each time, and still stronger lenses until the acuteness of vision is raised to ^JJ. But even when this point is reached the test does not stop, but is continued by the addition of still stronger lenses imtil the No. 20 line begins to be dimmed. Perhaps a + .50 D. or a + .75 D. lens stronger will be accepted than that which raises vision to normal; but as the amount of defect is not measured by the lens that first makes the No. 20 line read- able, but by the strongest lens with which this line remains so, the test is not ended until this latter lens is reached. NEVER TRY CONCAVE LENSES IN HYPERMETROPIA. The optician should be cautioned always in cases of sus- pected hypermetropia to commence the test with convex lenses, and if they improve vision, or at least if they do not make it worse, the refraction is proven to be hypennetropic. Whereas if weak concave lenses are tried first, they will most likely be accepted on account of the spasm of accommodation which is generally present ; and when once accepted they serve to stimulate the accommodation to still further contraction, and then if convex lenses are tried afterward, they will be promptly rejected; for the detection of hypermetropia by means of convex lenses depends upon a relaxation of the ac- commodation to the extent of the strength of the convex lenses used. In either case (with or without convex spherical lenses) HVPERMETROPIA. 91 the rays of light arc l)rought to a focus at tlie same i>lace, and vision remains the same. In the first case this was accomplislied l)y the refractive power supplied by the crystalline lens of the eye, and in tiic second case by the convex lens in front of the eye. lUit when concave lenses are used first they excite the accommodation and cause convex lenses to be rejected, and in this way the diagnosis of the case becomes doubtful, and the optician may he led into serious error. CAirioX IX CHANGIXG THK I.KNSKS. As the optician changes the test-lenses in front of the eye for stronger ones, he should not make too much of a jump or increase their strength too rapidly, else the ciliary muscle con- tract spasmodically and he fail to discover the hypermetroi)ia. But he should increase only .25 D. at a time, leaving each lens in front of the eye for a short space of time, thus giving the ciliary muscle an opportunity to relax and encouraging it to do so, and by thus chang-ing the lenses slowly and increasing their strength gradually, the test lenses will be used to the greatest jx^ssible advantage in developing and detecting hyper- metropia. THK METHOD BY OVER-CORRECTIOX, OR THE EOGGIXC. SYSTEM. After ascertaining the acuteness of vision, a strong convex lens is at once placed before the eye, about + 6 D. in ordinary cases, or even stronger if there is reason to suspect a marked degree of hypermetropia. Tliis blurs the letters on the dis- tance test card, and the patient involuntarily exclaims that he is unable to see with it. The optician encourages him to look quietly at the card for a moment or two without straining his eye, and after the eye recovers from the shock of suddenly placing such a strong lens before it, the vision may slightly improve. The action of the convex lens is to induce a relaxation of the accoinmodation, as only in this way can the vision be made even slightly better. The natural tendency for the ciliary muscle is to contract, but a contraction of this muscle when a convex lens is before the eve instanth- makes vision i'V IIVI-KKMI- TKoriA. very iiuu-h worse. 'I'lic eye is not slow to appreciate tliis tact. aiul then, as the natural instinct of the eye is for clear vision, the effort is made in the other direction, that is, in a relaxation of this nuiscle, which at once tends to slig-htl\- clear the vision. and thus a further relaxation is encourai^ed. Now a weak concave lens ( — .50 ]).) is ])laced over this convex one, and by diminishing- its strens.ith improves vision quite noticeably and encourages a still further lessening of acconuuodation. After this lens remains a l)rief moment, it is replaced by a — i D. lens, wliicii .-iffords another im])n)vement in vision and enables the patient to see more of the letters. Then — 1.50 D. is tried, followed by — 2D., — 2.50 D. and — 3 D., with amelioration of vision each time until the normal standard is reached, and then the difference between the con- vex and the concave lens w^ill be the measure of the hyper- metropia. AN ILLUSTRATION OF FOGGING. A patient presents himself with all the smptoms of hyper- metropia as they have been described in this chapter. On examination his acuteness of vision is found to be |^. Each eye is tested separately with convex lenses, but only + .50 D. is accepted and a stronger lens blurs the vision. Then the eyes are tried together, and it is found in binocular vision that they will bear + i D., but nothing- stronger. If the optician desires to make his examination thorough, he wall not stop here, but will make use of the fogging method. He places a + 6 D. lens in the trial frame, with which the patient is unable to read even the largest letter on the card at first, although after a moment he may be able to discern the form of the No. 200 letter. A — .50 D. lens is then placed in the front groove of the trial frame, which renders this letter clear and easily discerned. Then it is replaced by a — I D. lens, which brings out the No. 100 line. Next, a — 1.50 D. lens is tried with the effect of making- clear the No. 70 line of letters; a — 2D. clears up the No. 50 line, a — 2.50 D. the No. 40, and a — 3D. brings into view the No. 30 line, and, finally, a — 3.50 D. brings the vision up to |J clearly and distinctly. IIVPERMETROPIA. 93 Now what lias been done and wliat has been accom- plished? The + 6 D. lens first placed before the eye has been partially neutralized by the — 3.50 D. lens and reduced to + 2.50 D., with which vision is Ig, In other words, the eye has been led to accept a + 2.50 D. lens, with w^hich the acute- ness of vision is unimpaired, and hence this is the measure of the defect. TEST FOR HYPERMETROPIA BY SKIASCOPY, The essentials for the test by skiascopy are a darkened room, a bright light (either electric, gas or oil will answer), and a retinoscope, to which may be added the trial case. The distance of the optician from the patient is a matter of considerable interest, for which, however, there is no fixed rule, each observer within certain limits selecting his own distance. The beginner may try the method at different dis- tances, and then decide for himself at what distance he obtains the best results. When the plane mirror is used this is a com- paratively simple matter, but with a concave mirror any great variation in the distance requires a corresponding variation in the focus of the mirror; the nearer the optician approaches his patient the shorter should be the focus of the mirror, and the greater the distance the longer the focus. The preference of the writer is for a plane mirror and a distance of one meter, the advantages of this distance being that it is close enough to get a good view of the reflex and shadow, that a lens can be placed before the patient's eye and changed at will without requiring the optician to leave his seat, and that a uniform allowance of i D. is thus called for in the estimate. - The light should be steady, clear and white, and as bright as possible; the Welsbach light, the incandescent electric light or an Argand burner of either gas or oil will answer the pur- pose; and in order to obtain the brightest part of the flame, it is customary to use an asbestos chimney or screen with an aperture opposite the most brilliant part of the flame. The room should be darkened by removing all sources of light except the one in use. It is not essential that the ceil- 94 HVPERMETROPIA. ing- and walls of the room should be black, but the covering of all windows by black shades, that fit closely, will sufftce. The positian of the light is varied by different authorities. Formerly, the advice was given to place the light in such a position above the head, and slightly behind, that the patient's eyes will be in the shadow, and that no light can fall on the trial lenses that may be placed in the frame. Or the light may be close to the observer, and thence reflected on the patient's eyes, the optician's eye, the light, and the patient's eye all being on the same plane. The closer the light is to the mirror, the brighter will be the reflected rays. J ^eter This drawing shows the mirror at a distance of one meter from the eye under examination, and the darlv lines represent the reflected rays from the mirror, which illuminate the retina, and as in all hypermetropic eyes, focus behind the retina. The dotted lines indicate the diverging rays proceeding from the retina, and the convex lens of 3..50 D., which is placed in front of the eye. and which possesses just sufficient refractive power to bend these dotted diverging rays and bring them to a focus at the position of the mirror one meter away. METHOD OF CONDUCTING THE TEST. The patient and optician being seated at the proper dis- tance, the latter takes his retinoscopic mirror, holds it in front of his own eye, looks through the sight hole, and reflects the light on the patient's pupil, Avhich at once appears more or less brilliantly illuminated, according to the condition of the refraction of the eye, and the portion of the fundus which is being observed. If the optic disk is in the direct line of view, the examina- tion is more easily conducted; but as the refraction at the disk may possibly vary i D. or even 2 D. from that at the macula, the latter is really the proper part of the fundus to HVI'KRMKTROPIA. 95 be corrected, to obtain wbich the patient must look at tlie sight-hole of the mirror during the whole examination. The reflection from the eye of a blonde is much brighter than from a brunette, on account of the greater amount of pigment in the eye-ground of the latter. The reflection is much brighter in cases of low refractive error than in high degrees of defect, where it is dull. The sliadozu is the dark portion of the retina that mi- mediately surrounds the illumination; they adjoin each other, and the contrast between them is most marked and more easily recognized when the illumination is the brightest. It is this combination of light and shadow that gives the "shadow test" its name. In a darkened room the retina is in darkness, except that portion which is illuminated by the light from the mirror. As the mirror is rotated, the retinal illu- mination moves and shadow takes its place. It is this change of place of the illumination followed by the shadow, that causes it to be spoken of as the movement of the shadow. As the mirror is slow-ly and slightly rotated first one way and then the other, around an imaginary vertical axis, ihe light reflection moves with it across the face from right to left, and from left to right. Just here the beginner should know that the illumination of the patient's face alzivys moves in the same direction as the mirror is rotated, but in the pupil- lary area it may move in the same or in the opposite direction, as it is aflfected by the condition of the refraction. Hence when the movement of the illumination is spoken of. it is that w^hich is seen in the pupil and not on the face. When the movement of the retinal illumination is tin- same as the movement of the light on the patient's face, the case is presumably one of emmetropia or hypermetropia, in the determination of which convex glasses must be used and placed before the eye. The trial frame is used on the patient's face with a -}- i D. lens over the eye under examination, and the light is again reflected on the pupil, and the direction of the movement is again observed. If this lens causes the light to travel in a direction the reverse of that on the face, the refraction is proven to be emmetropic. Whereas if the shadow still moves in the same direction as the light, the eye is hyper- 06 inrERMETKOl'JA. nietropic, and the lens must be changed successively for stronger ones until finally a glass is reached which reverses the movement. now TO MAKE THE NECESSARY CALCULATIONS. \\'hcn this glass is found it is compared with the previous lens, and the refraction of the eye is between the two. In other words, the number of the lens is found between the weakest glass which reverses the movement of the reflection and the strongest glass which does not reverse it. If when a + 3.25 D. lens is placed in the trial frame, the illumination is dimin- ished in size and very faint, appears to move rapidly and zvith the light on the face, the hypermetropia is still slightly un- corrected, and a stronger lens must be found. If a + 3.75 lens is substituted for it, and the retinal illumination is then found to move opposite to the movement of the light on the face, the measure of the defect will be between the + 3.25 D. and the + 3.75 D., which is + 3.50 D. This lens has converged the emergent rays issuing from the patient's eye and brought them to a focus in the optician's eye, which is at a distance of one meter; and in so doing and fixing the far point at one meter, it has practically made the eye myopic to that extent, just one diopter. Therefore when the patient's vision is tested with the letters at twenty feet, this i D. of artificial myopia partly neutralizes the 3.50 D. of hypermetropia, and the result of adding — i D. to -f- 3.50 D. gives 2.50 D. as the amount of the hypermetropia. This -\- 2.50 D. lens, when placed before a hypermetropic eye, suffices to render parallel the divergent rays proceeding from it, and conversely would so refract parallel rays of light entering the eye, as to exactly focus them upon the retina. But the additional + i D. is necessary to refract the emergent rays still more in order to bring them to a focus at one meter. The reader who follows these explanations carefully will readily understand why the correcting glass should be i D. less than that shown by the retinoscope, and the writer de- sires to draw especial attention to this point, as it is one that is more or less confused in the mind of the beginner in retinoscopy. HYI'ERMETROPIA. 97 TEST FOR IIVPERMKTROI'IA 15 V THE OrilTII ALMOSCf )rE. The room should be darkened, and the same light can be used that was found available in the shadow test. It should be placed (by an adjustable bracket) on the same level a: the eye that is to be examined, and on the same side of the head. Patient and optician sit facing- each other and side by side. The pupil is then illuminated by reflecting- the light from the concave mirror, and the red reflex is obtained. If there are any opacities in any of the refracting media, they at once be- come apparent by marring the clearness of the reflex. Presuming there are none, the optician at once passes on to the direct nwthod of the use of the ophthalmoscope, which is the one preferred for estimating the refraction. This gives an upright, enlarged picture, but only a very small portion of the fundus is visible at one time. Tlie optician uses his right eye to examine the patient's right, and approaches as close as possible, all the while keeping the pupil well illumi- nated. The beginner finds some difficulty in keeping the light on the pupil as he approaches, and as soon as it loses its bright red reflex he may know he is at fault with the position of his mirror. In an emmetropic eye, parallel rays are brought to a focus exactly on the retina without any efifort of accommodation. Conversely, the rays proceeding from the retina of such an eye are bent by its refracting media in such a way as to issue from the eye parallel. THE OPTICAL PRINCIPLES INVOLVED IN THE OPTHALMOSCOPIC TEST. In hypermetropia the focus of parallel rays is behind the retina, and only convergent rays can be focused on the retina. As no such rays are present in nature, the hypermetropic eye is adapted for a condition that does not naturally exist. The rays proceeding from the retina of such an eye are bent by its refracting media, but as their power is less than normal, the rays emerge from the eye divergent, just as if they came from a point behind the eye. These diverging rays can be rendered parallel only by the interposition of a convex lens of the proper strength. 98 HYPKRMKTROI'IA. If the eye is view oil through the ophthahiioscope at a dis- tance of twelve or fourteen inches, the condition of the re- fraction may he determined by the appearance and behavior of the blood-vessels as they are seen at the fundus of the eve, that is. the direction in whicli they will travel upon the moving of the head of the observer. In hypernietropia a more or less clear view of the fundus can be obtained at this distance ^vith the mirror alone. The imag-e is enlarged, erect and virtual, and as the optician moves his head from side to side, the disk and blood-vessels will seem to move in the stnuc direction. In emmetropia the optician must approach much closer to the observed eye in order to get a distinct view of the disk and vessels, and then as he moves his head their behavior will be the same as in hypernietropia. The power of accommodation in the eyes of both patient and optician is supposed to be at rest. In order to favor the relaxation of the accommodation in the i^atient's eye, the room is darkened and he is requested to turn his eyes in a distant direction, without, however, endeavoring to fix any one par- ticular object in distinct vision. For the optician it is some- times a difificult matter to place the accommodation at rest, because, in looking at the fundus of the patient's eye, he is inclined to adjust his accommodation as for a near object; whereas he should endeavor to relax his eye and place it in the condition for viewing distant objects. If the fundus be viewed as at a near point, the amount of accommodation brought into play will render the optician's eye practically myopic, and this is the reason why so many beginners can get a clearer view of the eye-ground by rotating a weak concave lens in the sight- hole of the ophthalmoscope. Therefore, it should be borne in mind that the improvement caused by a concave lens must not be considered as proof positive of the existence of my- opia. RELAXATION OF THE ACCOMMODATIOX. The power to completely relax his ciliary muscle is a faculty that should be cultivated by the ophthalmoscopist; and as it is so essential in the determination of hypernietropia, the HYPERMETROPIA. 09 following procedures will be found of benefit in assisting to that end. The optician looks ui)wanl and at the same time holds above his eyes a white card on which there is a black spot. He then endeavors to relax his accommodation, and as soon as he succeeds the sjiot will appear double; then the card is to be lowered, the e>es following it, and as long as the spot continues to appear double he will know that his accommoda- tion is at rest. Another exercise which is adapted for the same purpose, is to hold a pen or pencil about ten inches in front of the face, and if the ciliary muscle can be relaxed and the vision adjusted for distance, the pencil will appear double, and will continue so as long as the ciliary muscle can be kept quiescent. Still another method of practicing the same thing is to hold a book as close to the eyes as possible ; then the observer is to commence to read, and while thus engaged he endeavors to look through the book or beyond it, when the letters will run together and become obscured, because when the accom- modation relaxes the letters are no longer focused upon the retina; at the same time the optician will probably feel that the act of convergence lessens and the eyes gradually turn out- w^ard until their visual axes assume a parallel position. By a frequent repetition of one or all of the above exer- cises, the beginner can learn to approximate an object close to his eyes, and at the same time keep his acconmiodation and convergence in abeyance. Having thus secured control of his accommodation, the optician will be in a position to esti- mate by the use of the ophthalmoscope the amount of hyper- metropia in any particular case. WHAT TO LOOK FOR. The optician should familiarize himself with the appear- ance of the normal fundus; first by a careful study of the colored plate given in a previous chapter, and then by actual use of the ophthalmoscope with healthy eyes. The optic disk, that is. the entrance of the optic nerve, is the object to be looked for. it being circular in shape and much lighter than the retina, which presents a bright, rose-red, granular appear- 100 HYPERMETROPIA. ance. In brunettes there is more pigment matter in the retina, which brings out in strong contrast the difference in color of the disk and the retina. The optician now endeavors to get a clear view of the details of the fundus, and if he and his patient are both em- metropic this is a comparatively simple matter. If the observer is not emmetropic, he must wear his correcting glasses. If he looks into an hypermetropic eye (of moderate degree) he will again see the features of the eye-ground clearly and distinctly, but by the involuntary use of his accommoda- tion. A distinct picture being thus obtained in both emme- tropia and hypermetropia, how can it be determined which condition is present? By the revolving of a convex lens into the sight-hole of the ophthalmoscope, and if the picture still continues as clear (or is made more distinct) the case is known to be one of hypermetropia. And the strongest convex lens with which the optician can get a clear view of the optic disk and the blood-vessels will be the measure of the defect, pre- suming that both persons have been able to relax their ciliary muscles. In order to insure an exact measurement of the patient's refraction by means of the ophthalmoscope, the advice is given by some authorities to use the region of the yellow spot for the examination. But unless the eye is under the influence of a. mydriatic, this is a difficult matter, because the pupil sharply contracts as soon as the yellow spot turns toward the mirror; and besides there is no marked feature here; such as a blood-vessel, which can be used for accurate focusing. For all practical purposes the optic disk will be entirely satisfactory for this examination, and preferably the side of the disk toward the temple, because its margin here is gener- ally well defined. The small blood-vessels as they pass over the edge of the disk are to be observed; this makes a delicate test, as the variation of but a fraction of a dioptric is sufficient to throw them in or out of focus. Tlie optic disk is seen if the patient turns his eye slightly inward toward the nose, while the yellow spot comes into view when he looks directly at the hole in the mirror, while the course of the main retinal vessels can be traced by the HYPERMETROPIA. 101 optician moving- his head, and directing the patient to turn his eye, in an appropriate direction as the course of each vessel is being followed. CHROMATIC TEST FOR IIVPERMETROPI A. This test has been fully described and illustrated with colored plates in the chapter on "Method of Examination." It is a ready and convenient test for detecting hypermetropia, in which defect the retina, being farther front than normal, approaches the focus of the blue rays, causing the flame to appear wath a blue center and a red border. Tlie convex lens that neutralizes the flame and fuses it into a single color will be the measure of the defect. In this illustration the rays are shown which emanate from the candle flame and pass through the perforations in the card, and, being bent by the refracting media of the eye, are focused on the retina of the emmetropic eye. which is shown by the dotted lines. The hypermetropic eye being flatter, its retina is farther forward, as shown by the black line, and the rays striking it before their union produce there two images of the flame, and there- fore to such a person the flame is seen double. SCIIEIXERS TEST. This test for hypermetropia is one that is not in common use, and yet it illustrates so beautifully certain optical princi- ples that it is desirable the optician should be familiar with it. A card with two small holes, so close together that rays passing through them will enter the pupil, is placed in front of the eye to be examined. Tlie patient looks through these holes at a candle flame twenty feet away, and if the eye is hypermetropic two flames are seen, instead of one as in emmetropia. The explanation of this phenomenon is as follows: the rays of light proceeding from the candle flame travel in all directions and fall upon the card, a few of them passing 102 HYPERMKTROriA. through the pcrkirations; ami if the eye is adapted to the llanie, that is, if it be eiiinietro])ic. these two sets of rays will exactly meet on the retina, and form there a single image of the flame. If, however, the eye be hypermetropic and the defect be not corrected by the accommodation, the two sets of rays will strike the retina before they have had the opportunity to meet, and each set will form an image of the flame. Tlie greater the degree of the hypermetropia, the farther apart the two images will be. Convex lenses are then taken from the trial case and placed between the card and the eye, and that convex lens which causes the flame to be seen singly will be the measure of the defect. DETECTION OF HYPERMETROPIA BY MEASURING THE AMPLI- TUDE OF ACCOMMODATION. The amplitude of accommodation is the power exerted by the eye to change its adjustment from a far point to the near point, and is measured by the closest point at which the patient is able to read the fine print. The lens whose refractive power corresponds to this focal distance will represent the amplitude of accommodation. For instance, if twenty inches is found to be the distance of the near point, the amplitude of accommodation would be 2 D. If the near point is thirteen inches, the accommodation is equal to a lens of 3 D.; and if the near point is ten inches, the accommodation is 4 D. In emmetropia the amount of amplitude of accommoda- tion is a constant one for the different ages all through life, as shown by the following table: 'ears. Amplitude of Years. Amplitude of Accommodation. Accommodation. 10 14 D. 40 4.50 D. 15 12 D. 45 3.50 D. 20 10 D. 50 2.50 D. 2.5 OD. 55 1.50 D. 30 7 n. 60 .50 D. 35 OD. This is the standard by which every case must be gauged, and any departure from which, at any certain age, can be readily detected. A hypermetropic eye requires some of its accommoda- tion for distant vision, and hence for close use there is a de- HYPERMKTROPIA. 103 ficiency of that aiiioinil ; tliorcforc the ani])HtU(le of accom- modation present in a hypermetropic eye at a s^iven age would be less than is indicated in the table for the same age; and the amount by which it is less would indicate the degree of defect. l*'or instance, if on examination a patient thirty }ears of age has a near point of eight inches, representing an ampli- tude of accommodation of 5 !)., it is at once evident there is a deficiency of 2 D., and a presumi)tion of the existence of a hypermetropia of that amount. A\'ith the same amplitude of acconnnodation it is evident that the near point is farther away in hypermetropia than in emmetropia. as is shown in the above instance, where the near point is at eight inches instead of five and a half inches, the normal distance. In this way the existence of a latent hyper- metropia can often be determined, that could not. iK'rhaps, be detected by the usual test with trial lenses. TIIK TKSTS FOR 1 1 V I'KKM ETROIM A CO.MPAKEI). In considering the value of the tests that have been de- scribed for the determination of hypermetropia, the optician soon discovers that the two objective tests (ophthalmoscopy and retinoscopy) are somewhat difificult to learn. Of course he knows that the theories involved and phenomena observed are simple and easily understood, but it requires much time and practice to become an expert in the use of these methods. Therefore they may be considered subordinate to the test by the trial lenses, which is really the decisive one. And then, finally, even this test yields to that which is given by the patient himself when he commences to wear the glasses which have been ordered. REMARKAHLE ACUTEXKSS OF VISION IX II VPERMETROPI A. In a description of this defect of hypermetropia it should be noted that hypermetropic eyes sometimes enjo\- an un- usual degree of aeuteness of sight, and, in fact, when young, they are very ai)t to boast of their power of vision. They can- not only read all the No. 20 line without an error when seated at twentv feet but will also call ofif the letters on the next line 104 HYPERMETROPIA. c|uitc as readily. The parents of such a boy will tell how the child can see things with an ease and distinctness which thev themselves do not possess. They may laugh at the suggestion of any defect in the eyes of their child, and ridicule the thought of glasses as long as the child can get along without them. I'REJUDICE AGAINST GLASSES. There is no use denying the universal prejudice that has existed in the public mind, but which, fortunately, is not so pronounced now as formerly that glasses are an injury when they can be avoided for fear the patient may become so de- pendent upon them as never to be able to remove them. This is certainly not good grounds for an argument, but the proper light in which the matter should be viewed is that if Nature is dependent upon a glass w^iich affords relief and removes strain, such means of assistance should not be withheld. If the pain in hip disease is arrested by a properly- adapted support, should the splint be denied the patient be- cause he feels his dependence upon it? Is there any more reason why a patient with defective eyes should go through life without the relief that glasses only can afford, simply because of unfounded prejudice against their use? A case is related of a physician who refused to allow an oculist to examine his children's eyes, with the statement that no child of his should ever wear glasses with his consent. The children suffered from weekly attacks of sick headaches, and finally one w^as fitted with a + 3.25 D. lens, another with the same sphere combined with 5° prisms, and the third was also highly hypermetropic and astigmatic. Immediate relief was afforded in each one of these cases by the correction of an optical defect which had rendered their early life one of suf- fering. This is not an uncommon experience w'ith oculists and opticians. SICK HEADACHES. There is every reason to believe that there are thousands of sufferers from sick headache who are struggling through life with an uncorrected hypermetropia, who have made un- successful efforts for relief at the hands of doctors and drugs. and who have in despair abandoned all hope of cure. This HYPERMETROPIA. 105 is an interesting study for the ambitious optician, and forms a wide and promising field for the exercise of his skill and judgment. The statement is made by eminent authorities that the gastric symptoms which accompany typical attacks of sick headache are not due to "biliousness," or "disordered liver," or "dyspeptic conditions," or "the use of tobacco to excess," or "living too high," but they are reflex in character, and, in the majority of cases, due to hypermetropia. These attacks often occur without any explainable cause, and they are sometimes even cured by eating, drinking or smoking, while at other times they are aggravated by similar indulgences. Every known remedy in the pharmacopoeia has been tried, at first with success, acting almost as specifics, and later prov- ing entirely valueless, until finally life is rendered really un- endurable. The brain and central nervous system preside over all the functions of life. If now^ this ruling spirit is disturbed by the irritation caused by a constant strain to use the eyes in the face of an uncorrected hypermetropia, may not this dis- turbance manifest itself by an interference with the normal functions, as shown by nausea, vomiting, dizziness, and other evidences of impaired animal life? This reasoning is plausi- ble, and although they are the views of an extremist, they contain much of truth, and suggest a train of thought and experiment that can be successfully carried out by every in- telligent optician. RECAPITULATORY REMARKS. Before concluding this chapter on hypermetropia. at the risk of possible repetition it seems desirable to mention again a few of the important points that should be borne in mind in adjusting glasses for the correction of this defect. In obtaining the liistory of the case the optician should ascertain whether or not the patient has been wearing glasses, and if so, what kind, what number, and how long. Even though they are entirely unsuitable, they may serve as a guide in making the test and prevent the prescription of sim- ilar glasses, which the optician might be led to give if he was not thus warned. lOG HYPERMETROPIA. In testing^ the vision at twenty feet, every letter in the No. 20 line may seem black and the outlines of the letters clearly (Jetined. and the i)resumption would be that the patient was emmetropic, hut he ////_23 28.05 " 14 5-74 28.56 " IS 6.28 29.10 " 16 6.83 29.65 " 17 7-41 30.23 " 18 8.03 30.85 " 19 8.65 31-47 " 20 9-31 32.13 " The antero-jX)steriar diameter of the normal eye is 22.82 mm., which is about iVu. ^^ ^^ i"ch. In the higher grades of myopia, an increase of i D. represents a much greater addition in length of the ball than in the lower grades. For instance, a myopia of i D. causes an increase of -^5^ of a millimeter, as compared with -jV^the enlargement in an eye of 20 D. myopia over one of 19 D., the increase in the higher degree being more than twice as great as in the commencement of the defect. The average increase for every dioptric of defect is about ^0^5 of a millimeter, which equals nearly ^j^ of an inch. In an organ so small as the eye, which measures less than an inch in diameter, the addition of even Jg- of an inch cannot be disregarded. And when we consider the eye as an optical instrument, comparable to a photographer's camera or a microscope, and when we call to mind how the slightest move- ment of the screw will throw both of these instruments out of focus, it can be readily understood that the addition of ^jj of an inch to the length of the eye-ball is sufficient to disturb the dioptric adjustment of the eye and to impair the clearness of the image formed upon its retina. In a myopia of 5 D. the amount of lengthening is if millimeters, or ^^ of an inch; in a myopia of 10 D. the amount is 3* millimeters, or nearly ^ of an inch; in 15 D, of myopia, 6\ millimeters, or \ of an inch; while in an extreme case of myopia of 20 D., 9f millimeters is added to the length of the ball, which means the addition of more than -^ of an inch, making such an eye measure i^^ inches as compared with || of an inch, which is the normal standard. A careful study of this table is interesting and important, and serves to impress upon the optician the actual organic changes in the coats and shape of the eye-ball, upon which the production of myopia depends. 117 CAUSES OV MYOPIA. The one great cause of myopia is loiio^-continued use of the eyes for small objects close at liand; and, therefore, myopia may be considered as a product of civilization — as a penalty of prog-ressiveness. The use of the eye for close vision calls for an effort of accommodation, and when long continued, may cause a spasm of the ciliary muscle. The adjustment of the dioptric apparatus of the eye for the divergent rays of near vision, transforms it temporarily into a condition similar to myopia; and if the accommodation continues its spasm and fails to relax, a condition of accommodative myopia is produced. In this case the eye-ball is not elongated and there is no real myopia, but all the symptoms are present and the defect is simulated by the spasm of accommodation. Tlie permanent production of real myopia depends upon the congestion, inflammation and giving way of the coats of the eye-ball. Tine ciliary muscle is connected with the choroid, and, therefore, in the exercise of the function of accommoda- tion there is a strain upon the latter; and when the eye is over- taxed, as is frequently the case with school children and those compelled to use their eyes continuously for near work, an inflammation of the choroid is apt to follow. In addition to this, the close position at which the object is held necessitates a marked convergence of the optic axes, which causes a strain of the muscles and a i)ressure upon the tunics of the ball. Then, too, the stooping position that is generally indulged in during such employment, also tends to increase the congestion and inflammation by favoring an ac- cumulation of blood in the eye. In this way a continuation of the congestion and pressure gradually leads to a l)ulging at the posterior pole of the eye. THE EFFECT OF SCHOOL LIFE UPON' THE SIGHT. There is no doubt that the origin of many distressing diseases can be traced to the school life of the sufferer. The pathological conditions are not in all cases the direct result of unsuitable school existence, but it may be tiiat the im- properly constructed school building;^ and badlx' managed 118 MYOPIA. school life simply fan into a dame the spark of heredity which many unfortunate children receive from diseased parents. The deleterious influence of education and intellectual advancement upon the bodily health is everywhere apparent. Tlie mind is cultivated at the expense of the body, and it almost seems as if mental advancement goes hand in hand with physical retrogression. Certain it is, that uneducated and untutored races present types of bodily development supe- rior to those nations that are renowned for civilization and knowledge. The eye furnishes a striking example of the truth of these statements. The vision of those persons who are engaged in farming and kindred occupations is but seldom impaired, while in savage and barbarous races the statement is made that myopia and astigmatism are positively unknown. We are com- pelled to regard school life as disastrously prolific of refractive errors, by far the most frequent of which is myopia. SCHOOL STATISTICS. As early as the beginning of the present century the fact was recognized that the oftentimes unnatural requirements of school life resulted in injury to the eyes of many of the chil- dren; and several writers in those early days called attention to these important matters and to the relation that seemed to exist between the demands of civilized life and the production of myopia. The statistics that have been compiled bearing on this subject are enormous. The examination of the eyes of more than ten thousand school children in Breslau and vicinity by Cohn, and the published results of his extensive investigations, in 1865 and 1866, called public attention tO' school hygiene and gave a great impetus to the discussion of this important sub- ject. Similar examinations have been repeated from time to time by other observers in dififerent cities, until at the present time the children who have been subjected to a study of ocular conditions by competent examiners for statistical purposes, compose an army of more than two hundred thousand. These investigations have occurred in all civilized countries, and have been made under all circumstances of age, sex, race, health. MYOPIA. 119 heredity and schot)! architecture and nianagcnicnt. Many of these investigations have been so arranged as to follow a cer- tain number of pupils from class to class and from school to school, and they all point to one inevitable conclusion, viz., that mental culture is obtained at the sacrifice of ocular per- fection, and that such imperfections are usually myopic in their nature. Certain facts have been cstal)lislK'(l by these investiga- tions, wliich may be brielly niontioned as follows: 1. The eye at birth is hypermetropic, and during early childhood the hypermetropic eyes greatly outnumbered the emme'tropic and myopic ones. An examination by one ob- serv^er of children three months old, showed them to be all hypermetropic. 2. Emmetropia was comparatively rare, but the percent- age of those eyes which most nearly approached this condi- tion remained almost uniform throughout school life. 3. Myopia was entirely absent, or very rare before the commencement of school life, and was found to increase steadily in percentage with the progress of the pupils in the schools, while the percentage of hypermetropia diminished in approximately the same degree. Not only does the num- ber of myopic scholars increase from the lowest to the highest schools, but the increase is in direct proportion to the length of time devoted to the strain of school life. We cannot burden this chapter with the statistics com- piled by the various European and American observers, but as Prof. Cohn's work was the most extensive and most not- able, and stands as the representative of all the others, we give his figures as follows : Primary schools 1.4 pcr cent, of myopia. Elementary schools 6.7 " Intermediate schools 10.3 High schools 19.7 Gymnasia 26.2 Universities 59.5 The fact that in the universities fifty-nine students out of every hundred are myopic is an appalling one, and when con- trasted with the small percentage in the primary schools (only 120 MYOPIA. one out of every hundred), there is certainly abundant food for the most serious thought, which appeals however more to those engaged in the education of cliiUlrcn tlian to us as opticians. GENESIS OF MYOPIA. The manner in which abnormal circumstances act in causing an elongation of the axis of the eye, which is the physical condition present in myopia, has been well described by Fenner in the following graphic words: "As a nation or community becomes wealthy, refined and elevated in social position, the inhabitants are more inclined to cultivate the intellectual faculties; hence they spend much time in close study, requiring a great and prolonged tension of accommodation in reading, writing, etc. They usually sit bending over a desk in stooping position, the abdominal organs are compressed, preventing the free return of the blood from the head. "The insufBcient illumination at many schools and col- leges necessitates the bringing of the eyes very near the book, so as to obtain a larger visual angle, and as the book usually rests on a desk or table, the head has to be bent over; this posture produces an increased flow of blood to the eyes, whilst the higher degree of convergence necessary causes an in- creased pressure of the lateral recti muscles on the equator of the globe, thus increasing the intra-ocular pressure. "The congestion of the fundus oculi causes softening of the scleral tissue, which gives way under the increased pres- sure, and the organ is elongated backward (a condition of posterior staphyloma) ; the other portions of the sclerotic coat are supported by the broad muscles. The retina is then pushed backward behind the focus of the dioptric apparatus. "When this condition once commences, all the causes which first gave rise to it, act with increased force. There is a greater stooping posture necessary, because the eyes have to be brought still nearer the object; an increased converg- ence is demanded, and the congestion of the fundus oculi in- creases; consequently the softening processes progressively augment, causing the posterior portion of the sclerotic to MYOPIA. 121 yield more and more. Hence myopia is usually progressive, particularly in its higher grades. "There is greater tendency to the development of this condition of the eye in youth from the causes above men- tioned, because then the scleral tissues are softer and conse- quently more yielding than in later life. With the increase of age this coat hardens, becomes firmer and better able to with- stand intraocular pressure; hence it is rare that the posterior staphyloma giving rise to near-sightedness commences after the twentieth year." V.IIV CHILDREN ARE MORE PRONE TO MYOPIA. From the foregoing statements that the development of myopia depends upon a daily and continuous use of the eyes upon small objects close at hand, accompanied by strong convergence and with the patient in a stooping posture, it might naturally be expected to find this error of refraction of frequent occurrence among tailors, seamstresses, embroidery and lace makers, and all artisans whose trades require accurate near-vision. But the fact is myopia is much more rare among these people than in the wealthier and more intellectual classes. This apparent paradox can be explained as follows: these working people do not engage in their occupations until they are of adult size, when the tissues of the sclerotic and the other coats of the eye have become suflficiently firm to resist the disturbing influences which their work engenders. While in the case of the higher classes, the eyes are exposed to the dan- gers of myopia at the tender age at which these children are usually placed at school. In addition to the difference in the ages of these two sets of people, there is probably another factor that is brought into action, and that is the well-known fact that when the mind is actively engaged in study, an increased quantity of blood flows through the brain, causing a temporary conges- tion, which is shared by the eye on account of its proximity, thus adding to the previous plethora of the fundus of this organ. 122 ANATOMICAL CHANCES IN THE FUNDUS OF THE MYOPIC EYE. In view of what has been said, that myopia means staphy- loma and that the degree of myopia corresponds to the amount of extension of the fundus, it follows that myopia and posterior staphyloma are almost synonymous terms, and it is evident that the myopic eye is essentially a diseased eye, more so than any other error of refraction. The invention of the ophthalmoscope places in our hands the means of observing the changes taking place in the fundus of the eye upon which the production of myopia depends, and of noting the progress of the morbid processes. The extension of the globe of the eye is at the expense of the sclerotic coat, which grows thinner and thinner, until in high degrees of myopia it becomes transparent, and some- times when the eye is turned inward, the dark pigment of the choroid becomes visible through it. As the property of the dense and firm sclerotic coat is to give the eye its form and to support its interior structure, it naturally follows if this pro- tecting coat be stretched at any part, the contents of the eye- ball lying adjacent to this will suffer a corresponding change in position. Thus it happens that the choroid coat also becomes ex- tended and atrophied, particularly on the outside of the optic disk, as well as in the region of the yellow spot. THE MY'OPIC CRESCENT. The choroid attains its greatest thinness around the outer edge of the optic disk, where it forms a white, shining con- centric disk, resembling a meniscus in shape. The dark pig- ment cells are obliterated, the small capillary blood-vessels no longer carry the red blood, and there remains the marble- white, crescent-shaped patch of atrophy. If the distension extends entirely around the disk, the atrophic portion becomes annular in shape. The ophthalmoscope admits of careful observation of these changes. Some remains of pigment are often seen about the convex border of the crescent. Although the atrophy usually assumes the crescentric form, vet it mav varv, some- MYOPIA. 123 times forming a complete ring around the disc as already stated, or extending outward in an irregular patch. This in- crease in atrophic surface around the optic nerve enlarges the size of the normal blind spot. The presence of the crescent just described depends largely upon the degree of myopia; in slight cases in young persons it may be entirely absent, but in cases of 6 D. and over in adult persons it is almost invariably present. The position of the yellow spot may also be changed; it approaches the posterior pole of the eye-ball until the visual line almost corresponds with the optic axis. In very high degrees of the defect, it may even pass to the inside of the axis of the ball. HEREDITY. JNIyopia is regarded as an hereditary disease, and there is a universal popular impression that the defect is handed down from parent to child. When a myopic patient is ques- tioned, he can usually name some other member of his family as being similarly affected, perhaps a parent or grandparent, an uncle or aunt, a brother or sister. But there are many difficulties that stand in the way of a thorough investigation of hereditary influence, and perhaps all that can be claimed is that a predisposition to myopia is often transmitted to posterity, and not the disease itself. So that it may be regarded as an established fact that myopia rarely develops in an emmetropic eye, and never in a hypermetropic eye, Avithout a predisposition to it derived from ancestors. rREVENTIVE MEASURES. Whatever an ounce of prevention may be to other mem- bers of the body, it certainly is worth many pounds of cure to the eye. This delicate organ will stand a great deal of use, and not a little abuse, but when once thrown off its balance, it very rarely can be brought back to its original perfection of action, and it becomes liable ever after to a return of disability of function. On this account and from the fact that modern civiliza- tion has imposed upon the eye an ever-increasing amount of strain, one might suppose that the greatest precaution would 124 MYOPIA. be observed to maintain the or^^an in a condition of healtli. And yet it is safe to say that there is no organ in the body, the welfare of which is so persistently neglected as the eye. It is not uncommon, and certainly not improper, to have the first teeth of children four and live years of age filled in- stead of extracted; while the eye, the most intellectual, the most apprehensive, and the most discriminating of all our organs, receives scarcely a passing thought, much less an ex- amination. now THE CHILD SUFFERS. It seems never to occur to parents that the principal agent in acquiring an education is the eye. The child is placed in school without the slightest inquiry on the part of either parent or teacher as to whether it has the normal amount of sight, w^hether it be near-sighted or far-sighted, whether vision is clear or blurred, whether it sees with one eye or two eyes, or whether the act of vision is accomplished at the expense of an unnatural strain upon the nervous system. It has been trutlifully said, and cannot be repeated too often, that "a near-sighted eye is a sick eye," and it not infre- quently happens that a near-sighted child is a sick child, the reason for which is as follows: a myopic boy is unable to successfully compete with his schoolmates in their usual games, for the reason that most of them lie beyond the range of his vision. Subjected to ridicule on the part of his com- panions for clumsiness and inaptitude, due to a defect of which neither he nor they are aware, he relinquishes in disgust one by one of the health-giving sports in which he can never hope to excel, and takes to books until reading becomes a passion. Not only the abstraction from fresh air and exercise, but the ver}- conditions under which the eyes are used, are detri- mental to the general health. The book is brought nearer the eye, the head is bent upon the chest or over the table, till the shoulders become curved and the chest contracted, and normal respiration is interfered with. Such a child cannot see clearly the features of his com- panions, his parents or his teachers, nor catch the ever-varying expression of the eye, or the subtle change in the muscles of the face, by which an idea is emphasized or a principle en- MYOPIA. 125 forced. His sense of the beautiful in nature is hampered and curtailed. Earth, sea and sky make up for him a world dif- ferent from that of his companions, and it is no wonder that his views of men and things are different also. He judges of men and their intentions rather by the sound of the voice than the expression of the face, and is apt for that reason to be suspicious of strangers. In unfamiliar neighbor- hoods and with insufficient light, he is timid and cautious. With all this studiousness and devotion to books, the state- ment is made that near-sighted people, as a whole, are not any more intellectual than those who have normal eyes, because studiousness and intellectuality are not always convertible terms, as most people think they are. Of course these remarks do not apply to those cases of myopia which have been corrected at the commencement of school life with the proper concave lenses, but to those other cases of the defect which exist among young and growing children and which, bejng neglected, gradually become worse as adult age is reached, ORIGIN OF THE TERM MYOPIA. In hypermetropia, as was demonstrated in the last chapter, the patient is able, by the use of the accommodation, to over- come the defect and maintain clear vision. But in myopia, on the contrary, the exercise of the accommodation would only make the eye more near-sighted; nor does the eye possess any other power of its own to correct this error of refraction, except that such a patient falls into the habit of half-closing the lids, or nipping them together. In this way the more cir- cumferential rays are cut of¥ and the central rays only are allowed to enter the eye, the lids thus forming a stenopaic apparatus to the improvement of the clearness of the image formed on the retina. This gives rise to the word myopia, which is derived from two Greek words, meaning to "contract or close the eve." 126 Diagram of a Myopic Eye, showing fhat the divergent rays wliicli proceed from F. P. (the far point) are exactly focused upon the retina HOW DIVERGENT RAYS ARE FOCUSED IN MYOPIA. When parallel rays pass through a convex lens, they are brought to a focus at a certain point on the other side of the lens, which is known as the principal focus of the lens. If divergent rays are made to pass through the same lens, the focus would be farther away; while in the case of convergent rays the focus would be nearer than the principal focus. The statement has been made in this chapter that in myopia the rays meet in front of the retina, but it should be remembered that this refers only to parallel rays, or to con- vergent rays which focus still farther in front. The focus of divergent rays is farther back than parallel, thus approaching the retina, and if of the proper degree of divergence will meet on this membrane. Now in nature there are no convergent rays of light ; such rays exist only when made so artificially. Hence we are inter- ested at the present time only in parallel and divergent rays, the two forms in which we find light to exist, the former pro- ceeding from distant objects and meeting in front of the retina of the myopic eye; the latter issuing from objects near at hand and focussing on the retina as shown by the diagram. There is in front of the myopic eye a certain space within which vision is clear and beyond which it becomes indistinct, the dividing line of which is marked by the far point, which varies with the degree of defect. The higher the grade of myopia the closer the far point, the lower the degree the more distant the far point. It follows from this that if any object can be brought close enough to be within the far point of any MYOPIA. 127 myopic eye, it will be clearly seen. While if it is moved farther away so as to get beyond the far point, the rays begin to lose their divergence and focus in front of the retina and vision is no longer distinct. Thus it is seen that the myope is shut up in a little world of his own, the limits of which are determined by the distance of the far point. In the correction of myopia, the concave lens that is pre- scribed causes the rays that pass through it to enter the eye divergently, thus throwing the focus back upon the retina, and restoring distant vision to normal clearness. PREVALENCE OF MYOPIA AND ITS COMPARATIVE FREQUENCY IN DIFFERENT CLASSES OF SOCIETY. ^lyopia is more common in the cities, and in those nations and among those classes of people, whose advanced civiliza- tion, and w^hose occupations require extended use of the eyes for close objects. It is not equally prevalent in all civilized countries, nor in all parts of the same country. It is much less frequently found among persons brought up in rural districts, or among those who devote themselves to occupations requiring but little use of sharp vision for small objects. On the contrary it is among this class that hyper- metropia prevails to a much greater extent. VISION OF MYOPES. It is not unusual to find in the slighter degrees of myopia, where the error of refraction is less than 2 D., that the patient himself is not conscious of its existence, until perhaps it is accidentally discovered when comparing distant vision with some emmetropic friend; or by tr>ing on the concave glasses of some myopic friend, when it is found that everything is more clearly seen and objects arc visible at greater distances. With such a myopia the patient will be able to read fine print without convex glasses until he is probably fifty or fifty- five years of age. Thus the late appearance of presbyopia will tend to compensate for the diminished range of vision for distant objects. It is for these reasons that Donders gives his preference to the slightly myopic eye, because he argued 128 MYOPIA. that the slight iiuhstinctness with which distant objects are seen in early life, is more than counterbalanced by the ability to read and write at a later period of life without the use of convex glasses. In higher degrees of myopia if there is a fair amplitude of acconunodation present, the patient naturally falls into the habit of bringing small objects close to the eyes, oftentimes much nearer than there is any necessity for, and as it is in- convenient to bring his book or work close to his eyes, he bends the body so as to assume a stooping position, the more so the higher the degree of defect. The half-closed lids and the wrinkling of the skin of the forehead, gives the features a peculiar expression, by which the myope can often be recognized; and this habit, like many others when once formed, is hard to abandon and is often kept up even after the myopia has been entirely corrected by con- cave glasses, and the necessity for using the lids as a stenopaic apparatus no longer exists. As has already been stated, objects situated beyond the far point are seen in diffusion circles; while within this point vision is just as good as in an emmetropic eye, or perhaps even a little better. Inasmuch as small objects in order to be sharply defined, must necessarily be held much closer in this defect than normal, the visual angle under which they are seen is proportionally larger; consequently the image formed on the retina is of greater size, thus impressing more of the percipient elements of the layer of rods and cones. In addition to this the pupil is more dilated in myopia, thus allowing additional light to enter the eye and enabling the patient to see with less illumination. But while near vision is possible with a feeble light, distant vision on the contrary is improved by a brilliant illumination, because the strong light contracts the pupil and thus diminishes the size of the diffusion circles. For this reason the myope can see very much better by looking through the pin-hole disk from the trial case. When the degree of myopia is greater than 6 D., there is generally more or less disturbance of near vision in addition to the impairment of distant vision, and this is not to be won- y\\o\'\.\. 129 dered at wlion the morbid clian,L;cs that have taken place at the fundus of the eye are euusidered. I'.xcessive use of the eyes in near vision i)roduces a fecHnj^- of strain and they become ])ainful : follo\vini>- which there apjiears redness of the con- junctiva and an increased llow of tears. Misc.M \()i.ri A.\ii:s. in all form of ametropia, but especiall\ in myopia, C(jui- plaints are often made of dark sjjots or lloating bodies, whicli make their a])pearance in the field of vision and dance before the e\es, and which have received the name of mnsccc ivlitaiitcs. The constant appearance of these floating sjjecks is a source of considerable aiuioyance and alarm to myopes, not only from the way in which they eng-age the attention, but also from the fears which they excite. They are variously described by different persons, and are most noticeable when the eyes are turned toward a white sur- face, such as a white-washed wall or ceiling, or a white cloud. Tlie\- follow the movements of the eye, and are especially annoying dm-ing the act of reading as they float across the ])age. Thev do not, however, interfere with vision, as it is characteristic of them that they never cross the axis of vision, nor obscure or conceal the object looked at. but rather move about the lateral jiortions of the field. There is no real opacity of the vitreous humor, and an examination by the ophthalmoscope fails to detect in these cases any floating opa(|ue particles. They are caused by shadows thrown upon the retina by very minute particles in the vitreous body, perhaps the remains of embryonic tissues. They are more visible to myopic persons than to others, be- cause of the greater length of the eye-ball, thus allowing a shadow of larger size to he cast upon the retina. The nund)er of these spots may be increased by any condition which dis- turbs the balance of the circulation and thus alters the density of the fluids within the eye. If not excessive in size or nund)er. these spots may l)e regarded as more or less physiological and the effort must be made by the individual to ignore them. I'atients often complain of the exaggerated and fantastic shai)es they assume. 130 MYOPIA. ascrihiiij;- tlioni to disorders of digestion and torpidity of the liver. r>ut when they are al)uiulant and increasing-, they may indicate serious structural chang-e, and should lead to a careful examination by a competent oculist. Donders says: "I have seen instances in which anxietv about muscce vt)litantes aniountetl to true monomania, against which all reasoning and the most direct demonstrations were in vain." Any marked increase in the size and number of these spots may be regarded as evidence of morbid changes taking place in the vitreous humor, and if they become so bad as to seri- ously disturb vision, an examination by the ophthalmoscope will generally reveal turbidity in this humor. Sometimes there arc such subjective symptoms as sparks, luminous chains, flashes of lig^ht, brightly illuminated white or colored rings, which often appear in the field of vision : they are more notice- able in darkness than in daylight and are, of course, very alarming to the sufferer. Their appearance is an indication that some serious condition is impending in the fundus of the eye, and which may result in amblyopia. Even after the onset of these unpleasant symptoms, if great care is exercised in the use of the eyes and all excesses and irregularities of habits are avoided, vision may be preser\'ed in a fairly good condition for a long time. The myopic eye is more liable to be attacked by disease of its internal structures than is the emmetropic eye: as choroi- ditis, which often leads on tO' hyalitis and inflammation of the vitreous, conditions which are serioiis and very much to be dreaded: hence the great importance of care in the use of such eyes, which require careful watching in order that complica- tions may be early detected and receive skillful treatment. DETERMINATION OF THE ENISTENCE OF MYOPIA. The presence of myopia and its degree can be readily de- termined by the test letters of Snellen, which are hanging on the wall twenty feet away. If the patient is able to read the No. 20 line there can be no myopia; if, however, he cannot see the letters on this line, but can perhaps barely distinguish some of the larger lines, a MYOPIA. 131 weak convex lens is placed before the eyes; this at once blurs the vision and excludes hypernietropia. A convex lens is used as a matter of proper routine, even though the symptoms all indicate myopia, in order to escape the grievous error of mis- taking hypcrmetropia for myopia, as has been frequently done, to the discredit of the optician and the suffering of the patient. After this procedure the way is clear tor the use of con- cave lenses; a weak one is first tried which instantly clears vision and enables more letters to be seen. A stronger one is used with the result of a still greater improvement; thus by a gradual increase in the power of the lenses the acuteness of vision is brought up to |g clearly and sharply. This proves the existence of myopia, and the number of glasses will indi- cate the degree of the defect. As soon as the vision is raised to fg, the optician must stop, because then he has measured the grade of the myopia. In this defect it is a not uncommon thing for glasses to be prescribed very much stronger than are really necessary. If the patient is not old, and the power of accommodation unim- paired, an increase in the strength of the glasses will allow the distant type to be seen equally well or, perhaps, even a little better. When a concave lens is placed before a myopic eye of greater strength than is necessary to neutralize the defect, the eye is rendered hypermetropic and the ciliary muscle is called into action to overcome the diminishing effect of the minus lens, just as is the case in hypernietropia. This tension of the accommodation carries with it a contraction of the pupil (which in myopia is apt to be large), thus cutting of the peripheral rays and acting on the principle of the pin-hole disk, improves the distant vision. Hence there is a constant tend- ency for the glasses chosen in myopia to be stronger than are necessary, and such glasses at once begin to strain and irritate the eye. This logically leads to the rule that is laid down in myopia. that tJw very zvcakcst glasses with which the No. 20 line can be seen at twenty feet, are the proper ones to prescribe. In hypcrmetropia, it will be remembered, the strongest convex glasses which were accepted at twenty feet, were recom- 132 MYoriA. mended; in myopia, the weakest concave glasses. The reason is the same in both cases: to assist the accommodation or at least to avoid overtaxing ii. Tlie stronger the convex glasses the more support given to ilic ciliary muscle; the weaker the concave glasses the less tax upon this muscle. Dl.Vf.NOSIS OF MYOPIA. The diagnosis of myopia is not usual!}- a difficult matter. Distant vision is below the standard, and is at once raised to normal by the proper concave lenses. The impairment of dis- tant vision by itself is not an evidence of myopia, because this may be present in a great many other conditions. But when this diminished acuteness of vision instantly yields to the proper concave lenses, the proof is positive that the case is one of myopia and nothing else. In cases of impaired vision from other causes, the application of concave lenses will pro- duce little if any improvement. In the chapter on hypermetropia great stress was laid on the importance of distinguishing that defect from myopia, and the reader was warned that impaired distant vision and hold- ing objects close to the eyes, did not necessarily indicate myopia, but might occur in hypermetropia. The skilled and wide-awake optician will hardly fall into this error, and yet it has happened quite often among mere spectacle sellers, and thus tends to bring discredit upon opticians as a class. In any case of impaired vision where it is desired to measure the refraction by trial lenses, the invariable rule is to commence the test zcith convex lenses, and if they are accepted at all, the case is regarded as one of hypermetropia and concave lenses must not be tried. Perchance the latter were placed before the eye, they w'ould most likely be accepted also; then the case would be obscured and the optician in a quandary — convex and concave lenses both accepted, which is correct? But if the rule just mentioned be adhered to, the case is kept free from any such doubt. Then, if convex lenses are absolutely rejected, it is proper to try concaves, and if the latter raise the vision to normal, myopia must be the defect that is present. 133 MYOPIA AND AMIiLVOPIA. The term amblyopia usually sig-nifies (Uiihiicss of vision, and as this is the one prominent symptom of myopia, there is some danger that the two conditions may be confounded. In both cases the acuteness of vision is impaired, and there is the tendency to bring small objects very close to the eyes in order to get the benefit of the magnified retinal images. Strictly speaking, amblyopia i's only a symptom; it is a term used to express the defective vision from which the patient suflfers, which is not dependent upon an error of refraction, but is due to functional disturbance or disease of some part of the visual apparatus, either the retina, the optic nerve or the brain. It is possible that this condition may exist without any evi- dences of it visible to the ophthalmoscope, although wc usually expect to find some atrophy of the optic nerve. Tliis is not the place to give a detailed description of amblyopia, but wc will simply mention some of the forms in which it occurs: congenital or acquired, temporary or per- manent, and symmetrical or non-symmetrical, .linblvopia ex anopsia is due to lack of use of eyes; reflex amblyopia to irrita- tions in some other part of the body; traumatic amblyopia to injury; urcrmic amblyopia to kidney disease; tobacco and alcoJwl amblyopia to abuse of these agents; Jiysferical amblyopia, Jiiglit- biindiicss, day-blinditess. etc. The one diagnostic feature of amblyopia b\- which the optician will be able to recognize it. is its inability to respond to any glass that may be placed before it, and the failure of the pin-hole disk to afTord the slightest improvement in the acuteness of vision. By attention to these points myopia can always be readily distinguished from amblyopia. Ni:.\R x'lsiox IS (tOon. While in myopia the distaiU vision is very nnich impaired, at the same time the near vision is quite gooresbyopic chanj^es. The actual myopia has not l)een diniinishe(l, as shown by the far point of distinct vision remaining at the same place, all the changes and apparent improvement ha\ing taken place in the position of the near point. Tliere is one change in the eye that accompanies age. that does seem to improve the vision of the myopic eye, and that depends on the size of. the pupil. As years creep on the pupil contracts, sometimes almost to a pin point, thus cutting ofif some of the circles of diffusion which are so annoying to a myope when looking at a distance, and in this way clearing the vision by allowing only the central rays to pass, but with- out in any wa\' intluencing the degree of nnopia. EFjn:tT OF lIOLDlXt; TKK I'.OOK FARTHER AWAY. Tlie attem])t has been made to lessen the amount of myopia l)y recpiiring the patient to hold his book or keep his work at a greater distance, and thus after a few weeks' prac- tice the myope is often able to read considerably farther oft, and he thinks that his defect has diminished; but the experi- enced optician knows that he has been holding his book closer than is really necessary (as all myopes are apt to do), and that, furthermore, the degree of defect is measured by the far point instead of the near point, and that for any distance less than the former the accommodation is brought into action. Suppose an eninietrope is accustomed to hold his book twelve inches from his eyes, and by the advice of some friend he tries to habituate himself to read at a distance of sixteen inches instead; he simply reads with less effort of accommo- dation. So it is with a myope; if he increases the distance at which his book is ordinarily held, he simply sees with less exercise of accommodative power. No matter where the reading is held, the normal eye still remains emmetropic and the near-sighted eye is no less myopic, as evidenced by its far point being mi- changed in position. 138 MYOPIA. W'liilc this plan of treatment of holding the book at the greatest jiossible distance does not diminish the degree of the myopia, yet it is most timely advice for the myope to act upon, and it yields most excellent results in checking the prog- ress of the organic changes taking place in the fundus of the eye. It lessens the amount of convergence needed, and thus removes a great part of the pressure of the lateral mus- cles on the ball, while the erect position of the head retards the flow of blood to the already congested tissues, and thus restrains the softening processes upon which the giving way of the scleral tissues mainly depend. Therefore, the myope should be instructed to cultivate the habit of keeping his book and work as far from his eye as possible. MYOPIA NOT DEPEXDEXT UPOX COXVEXITY OF THE CORNEA. Formerly myopia was thought to be due to an excessive convexity of the cornea, and systematic efforts were made to lessen this by compression; but now since the defect is known to be dependent upon an extension of the posterior walls of the eye, it becomes apparent that such treatment is not only useless, but injurious, because the pressure might have a tend- ency to still further increase the elongation. jMyopia then is incurable, and only the lower grades are neutralized (and that but partially) by the compensation of senile changes during the later years of life. As the eye then cannot be restored to a normal condition, the management must consist in en- deavoring to arrest the progress of the abnormal changes, and at the same time to render vision easy and comfortable by neutralizing the error of refraction, as far as it can be done without injury to the eyes, and to increase the distance of the near point in order to diminish the excessive convergence and thus lessen the tension of the recti muscles, so as to remove their pressure from the ball. DISTANT VISION I:MPAIRED. To all near-sighted persons distant objects appear as in a fog, which increases with the degree of defect until even close objects present blurred outlines. Where the myopia is but slight, there is so little inconvenience that the patient himself MYOPIA. 139 may not be aware of liis defect until contrasted with the sharper sight of some friend. On the other hand, a highly myopic person will be unable to distinguish the features of a person who is no farther away than three or four feet. The first intimation that a child's eyes are growing defec- tive comes in the form of a complaint that the blackboard in the school-room, which could be clearly seen last year, is now very much blurred when viewed from the same desk, and the teacher is requested to allow a change of seats, nearer to the board, in order that the letters and figures upon it may be visible to the pupil. A little questioning will develop the fact that the child cannot see faces across the street and cannot even recognize his own parents at a distance. Now that attention has been called to the matter, it is noticed that in reading and studying at home the book is held much closer than formerly. If the parents themselves are myopic (as is not unlikely) they recognize the symptoms in their child as corresponding with their own myopic con- dition. Probably then the parent tests the child with his con- cave lenses, and if distant objects are brought out clearly a similar pair are purchased for the child. But this is a very improper and injudicious thing for the parent to do, and it is a well-established rule that concave glasses should never be supplied to a child except after a most careful and thorough examination by some one especially skilled in this line. It is possible there may be no myopia at all, but only a condition simulating it, dependent upon a spasm of accommodation, and if concave glasses were given under such circumstances the eyes would suffer irreparable injury. Such a case of spasm of the accommodation may present all the symptoms of myopia, so much so that even an expert refrac- tionist may almost be misled. But if the symptoms ar^ rightly interpreted and the condition early recognized, the danger of a confirmed defect may be averted. Whereas, if improperly managed, the defect which at first was only apparent becomes real and the vision gradually grows worse and worse. 140 SKfOXD SIGHT. This term is applied to those cases occurring in persons of advanced years who have been using- the regular convex lenses for the correction of their preslivopia. and who begin to find that their glasses are too strong; that they can read better with weaker ones, or perhaps with none at all. In other words, it is a return of reading vision late in life, and persons of advanced years are able to dispense with their cus- tomary convex lenses. But it should be remembered that this improvement in near vision is accompanied by a corre- sponding impairment of distant vision. The explanation of this (seemingly mysterious) occurrence is as follows: Ordinarily in old age the crystalline lens has become harder and denser and flatter, thus crippling the act of accommodation and necessitating the use of convex glasses to supplement it. This is a physiological change which occurs in every eye without exception. Now in certain cases the lens commences to imbibe fluid and to lose its dryness and hardness. This is accompanied by swelling of this humor, which is made possible by the elas- ticity of its capsule. Then, instead of being hard and flat, it is soft and swollen, and having become more convex it has increased its refracting and magnifying pow-er. This is the first step in the formation of cataract, although for many months and even years the lens may retain its transparency, even though altered in shape and consistency. But sooner or later opaque streaks or spots begin to make their appearance in it, and gradually the whole lens loses its clearness, and W'hen it has become entirely opacjue the condition is known as cataract. The statement has been made that when second sight makes its appearance before seventy, it foreshadows blindness from cataract in a comparatively short time — perhaps in six months, certainly within a few years. When the privilege of second sight first makes its appear- ance in extreme old age, that is in persons of eighty years and upward, the pathological changes in the lens are not likely to progress very rapidly, and the eyes will probably last as long MVoriA. 141 as the patient does, because the debihty of old age is apt to prove fatal before the opacity in the lens has made sufficient advance to restrict the sight. Concave lenses, for a longer (jr shorter lime, will iiii])rove the distant vision in these cases, just as in regular myopia, while reading may be possil)le without any glasses. But after a time, as the degeneration in the lens substance progresses, the passage of light to the retina is impeded and obstructed, and then vision becomes impaired both near and far, and glasses are no longer of any assistance. TIIK FAR POIXT Till': MKASl'RE OF Till-; MYOPIA. The distance of the far pcjint re])resents very closely the grade of the myopia, and therefore in order to save time and to quickly determine the approximate glass required in any case of myopia under examinatioii, without going through the process of trying a great many different numbers of glasses, a procedure both tedious to the patient and tiresome to the op- tician, the far point can be soon located and the extent of the defect at once becomes apparent. The patient is recjuested to read small-sized print, not necessarily the finest on the reading card, but somewhat smaller than the letters on this page, while the card is slowly moved away to the farthest distance from the eyes at which the letters still remain legible. If the myopia be of high de- gree and the near point very close to the eyes, the very smallest print can be used. If ten inches is found by this means to be the far ])oint, then 4 I), is the ai)])n).\imate measure of the myopia and a concave lens of that number is the i)roper cor- rection, or nearly so. In order to determine if such glass is the one that ought to be prescribed, it is placed before the eye of the patient, who is requested to look at the test-card, hanging twenty feet away, and read the lowest line he can make out; and then by trying alternately weak convex and weak concave lenses, placed be- fore the original glass, the proper number is soon determined. If the — 4 D. lens affords a vision of |o, a + .25 D. is placed before it. and if the No. 20 line still remains legible, then a -^ .50 I), is tried. If this dulls the vision (juite notice- 142 MYOPIA. ably, then the — 4 D. lens reduced by the + .25 D. would be the proper correction, and the prescription would be — 3.75 D.. because the rule in myopia is to order the very weakest glass with which satisfactory vision is possible. If, however, the — 4 D. lens does not raise the acuteness of vision to f^, then a — .25 D. is placed before it; this im- proves vision slig-htly, but still it is not up to the normal standard. Then a — .50 D. is tried, and this brino^s out the (Oe Wccker and Fuchs.) The Posterior Staphyloma of Myopia, show- ing not only the white crescent around the optic disc, but also white patches of atrophic choroiditis in the region of the yellow spot, and general exposure of the choroidal vessels by absorption of the retinal pigment epithe- lium. No. 20 line clearly, every letter being sharp and distinct. This proves that the first lens is not quite sufficient to entirel\" correct the refractive error, and a higher number must be sub- stituted, which we have found to be — 4.50 D. EXPLAXATIOX OF THE FAR POINT. The myopic eye is at rest when adjusted for its far point, just as an emmetropic eye is at rest when adjusted for infinite distance ; the divergent rays from the far point in the first case, and the parallel rays from infinity in the second case, being MYOPIA. 143 each focused on the retinae of their respective eyes without any effort of accommodation. Now, when a concave lens of the projaer focal distance is placed before the eye, the rays that pass through it from a distance will assume the same divergence as if they proceeded from the far point, and hence will be exactly focused upon the retina in the same way. Therefore, the parallel rays from a distance, after having been made artificially divergent, will afford distinct vision of the remote objects from which they proceed; just as in the case of the naturally divergent rays from a close point, which enable near objects to be clearly seen. This will explain why a far point of ten inches indicates a myopia of 4 D., and why a concave lens of the latter strength will correct the defect, and is a beautiful illustration of the adaptation of the refractive properties of lenses to the correc- tion of the errors of refraction of the human eye. WIIV MYOPIC EYES ARE REGARDED AS STRON'G EYES. There is a widely prevalent, popular notion that the eye of the myope is superior in strength to any other form of eye- ball. Notwithstanding the statement that has already been made that such an eye is a diseased eye, there is some founda- tion for this idea to become fixed in the public mind, in that the myope, more readily than the emmetrope. can distinguish minute objects, in the examination of which he is able to bring them much closer to his eyes, just as an emmetrope would be compelled to place a magnifying glass before his eye for the same purpose. This proximity increases the size of the image formed on the retina as well as the quantity of light reflected upon it, and as a consequence vision is made much more distinct. The dilated pupil, which is common in myopia, allows of a still further increase in the illumination. If an optical student (who is emmetropic) desires to test for himself the supposed superiority of the myopic eye, he can make himself artificially near-sighted by placing before his eyes a convex lens; in this way an addition is made to the re- fractive power of the eye, parallel rays are brought to a focus in front of the retina, distant vision is verv nuich blurred, and 144 MvoriA. even near vision is not entirely satisfactory. Such an experi- ment will tend to demonstrate the fact that the apparent supe- riority of the myopic eye is more fancied than real, except in slight degrees (2 D. or 3 1). or less). In these latter cases it is not uncoininon to find many per- sons who are utterly unconscious of any defect in their sight. Not having- an\ sjjccial need for sharp distant vision, they walk along the streets without a suspicion that others can see better than themselves. Only a few moments ago the writer had an illustration of this fact in his own office: a lady had com- pound myopic astigmatism and a visual acuteness of only j%%. Very naturally and properly we suggested glasses for constant wear and to improve distant vision. The lady indignantly re- pelled the suggestion, and going to the window she pulled aside the lace curtain and triumphantly exclaimed: "l don't need glasses for distant vision; 1 can see those numbers on the doors (they were very large), and if I was acquainted with those people I could recognize every one of them. My sight is all right; all 1 need is glasses for reading." Such a remark seemed ridiculous from a patient whose acuteness of vision was only ^W, but she w^as so determined that it seemed useless to argue with her. PROGESSni-: .MYOPIA. Myopia is a defect which does not decrease in degree; in fact, it even does not usually remain stationary, but its natural tendency is to increase. Such a condition is more than a simple error of refraction ; it is really a disease, and one that is fraught with many dangers to the eye. The optical characteristic of a myopic eye is that the posi- ti(jn of the retina is behind the focus of parallel rays; its anatomical and pathological characteristic is that this departure of the retina from its normal condition is due to a distention of the eye-ball, caused by a giving way of the coats of the ball at the fundus. As the membranes thus become attenuated, their power of resistance is at the same time diminished; in the face of this fact it is hardly to be expected that the trouble would remain stationary, when all the conditions are favorable for its increase. As the distention grows the myopia progresses, de- pendent upon a real disease of the eye. MVoriA. Ho On account of the elongation of the niyopic eye-hall in its antero-posterior diameter, rcsenihling somewhat the shape of an egg, its very form causes it to sufifer its greatest pressure backward, niis fact, together with that mentioned above (thinning of the coats of the eye and diminished power of re- sistance), will account for the progressive tendency of myopia. Of course, it can be easily understood that the higher the degree of myopia the more likely it is to assume the progressive form, even in more advanced years; while in youth almost every case of myopia shows a tendency to be progressive, and this is really the critical period for the myopic eye. The temi progressive myopia is reserved for those cases where the defect increases rapidly and is accompanied by symptoms of congestion and irritation, and does not apply to those cases where the progress of the defect is very slow and where the eye is free from all unpleasant symptoms. POSTERIOR .STAPHYLOMA. The general acceptance of posterior staphyloma as the anatomical basis of myopia rests upon two factors: 1. Descriptions of myopic eyes after death. 2. Ophthalmoscopic examinations during life. Myopic eyes of low or medium degrees (such as are usually acquired during school life) do not present this con- dition of posterior staphyloma, but it is always found in eyes having a myopia exceeding lo D. Tlie axial diameter of a normal eye is about 23 mm., which is considerably increased by the presence of posterior staphy- loma; of the recorded cases the shortest measured 27 mm. and the longest 32 mm. corresponding respectively to a myo])ia of II D. and of 20 D. As the thinning of the w^alls of the eye in these cases usually extends forward, the transverse diameter is also, as a rule, greater than normal, ranging from 24^ mm. to 28 mm., as compared with 22 mm. to 23 nmi., the normal measure. The ophthalmoscopic appearances of posterior staphyloma are marked and unmistakable. The characteristic symptom is a white crescent at the edge of the optic disk, generally at the outer side. This crescent varies greatlv in size, from a small 14G MYOl'IA. arc to a large zone, and may extend all art)und the disk, and even encroach on the region of the yellow si>ot, its greatest extent being always in this direction. Its edges may be sharply and distinctly defined, or may be irregular and gradn- allv merge in the surrounding healthy structure. There may be patches of pigment about the margin of the white crescent, or scattered over its surface. The crescent itself is of a brilliant white color, which makes the disk by contrast appear abnormally pink. On acount of this white- ness of the background, the small blood-vessels that pass over it are rendered more visible and are more easily dis- cerned than elsewhere on the retina. The whiteness is due to a thinning and an atrophy of the substance of the choroid, which, indeed, may be found entirely lacking at this spot, thus allowing the glistening sclerotic to come into view. Hence the white crescent is simply a portion of the sclerotic, which, for the reasons mentioned above, becomes abnormally visible. On account of the wasting of the choroid there is an absence of the pigment cells, and this removal of the natural protection against excessive light gives rise to the sense of glare which such patients frequently complain of. As might be expected from this, the sight of these myopes is often much improved by a tinted glass, which, under the circumstances, is not only allowable but advisable. DEGREE OF MYOPIA. The writer has frequently asked the following question of his optical students, "Upon what does the degree of myopia depend?" and the almost invariable answer has been, "The distance of the far point." This shows an incorrect concep- tion of the point involved. The location of the far point simply indicates or represents the amount of the myopia, which de- pends upon the distance of the focus of parallel rays in front of the retina. The nearer the focus is to this membrane the lower the degree of defect; the farther the focus is removed from it, the higher the grade of myopia. This, distance of the focus cannot be directly estimated, but can be determined indirectly by measuring the excess of MYOPIA. 147 refractive power. When tlie refraction of the eye exactly cor- responds with the lengtli of the optic axis, the condition is on'i of emmetropia; when the former exceeds the latter, the eye is known as a myopic one, and the concave lens that neutralizes the surplus will indicate the grade of myopia. Suppose a — 4 D. lens is required: this proves that there is a myopia of 4 D., and that there is an excess of refractive power of 4 D., which causes parallel rays to focus in front of the retina. The concave lens diminishes the refraction of the eye and gives to parallel rays sufficient divergence to throw their focus back upon the retina and thus afford clear vision. APPARENT OR ACCOMMODATIVE MYOPIA. The attention of the optician should be called to a condi- tion of apparent or false myopia, which is not myopia at all, but is made to simulate it on account of a spasm of the accommodation, by means of which the refraction of the eye is increased and parallel rays are brought to a focus in front of the retina. Ordinarily the ciliary muscle acts just sufficiently to focus divergent rays on the yellow spot and to adjust the eye for the every-day purposes of close vision. But this little muscle may fall into a condition of abnormal activity, known as spasm of the accommodation, where the muscle refuses to relax and continues indefinitely to keep the eye in a condition of over-refraction. This is the optical condition present in myopia, and gives rise to all the symptoms of this defect. This ciliary spasm may occur in emmetropia or more often in hypermetropia, as explained in the last chapter, where we gave warning of the danger of mistaking hypermetropia for myopia. Spasm of the acconnnodation is of more frequent occur- rence than is generally supposed, and in addition to the appar- ent myopia which it causes, also gives rise to marked symp- toms of asthenopia during reading or close work. The pupil is contracted and the ophthalmoscope will sliow con- gestion of the optic disk and retina. When the vision of such a patient is tested with the trial lenses there will be noticeable variations in tlie appar- 14S MYOI'IA. cut refraction: sonictinus lie will prefer one glass, some- times another. When the amplitude of accoiiimodation is measured there will be (juite a discrepancy between the i>osition of the far point and the degree of apparent myopia. I'or instance, the location of the far point may be ten inches from the eye, which would lead to a suspicion of a myopia of 4 D. But when the acuteness of vision is taken, such an error would be at once discovered. The patient can read all the letters on the test card, and only a weak concave lens is required (perhaps — i D.) to raise the vision to the normal of .?[}. ]n this way the diagnosis between real myopia and apparent m}opia due to spasm can often be made. The fact should not be overlooked that spasm of the ciliary nniscle may be dependent upon an insufificiency of the internal recti muscles. The excessive muscular effort required to maintain the necessary degree of convergence carries with it an extreme contraction of the ciliary. Just as in hyperme- tropia the extra accommodation causes an extra convergence which may result in convergent strabismus: in both instances produced by the close relation which naturally exists between the functions of accommodation and convergence. In these cases a pair of prisms, bases in, may assist in relaxing the ciliary spasm. Spasm of accommodation is most apt to occur in nervous individuals, when the system is enfeebled or the nervous force exhausted; and, strange to say, the degree of spasm bears no relation to the vigor of the ciliary muscle. In fact, it is usually found in connection with a weakened accommodation, and instead of being an evidence of extra strength, must be regarded as an indication of nervous debility. This is proven by the fact that eyes exhausted by overwork are the ones that are subject to spasm, and the accompanying asthenopia tends tO' increase the spasmodic action. The treatment of cases of spasm of accommodation will oftentimes tax the skill and ingenuity of the optician. One method of management consists in the use of convex lenses, a moderately strong pair for reading and a weak pair for distance. As is well known, the use of the convex lenses con- stantly and persistently encourages a relaxation of the spasm. MYOl'IA. HH and the patient who was apparently near-sighted, is soon able to read the No. 20 line without the concave glasses that were formerly necessary. Of course, the wearing of convex lenses in this way makes vision indistinct, and the patient is apt to rebel. Sometimes, with intelligent persons, if the rationale of the treatment is ex- plained, their cooperation may be secured. But if not, the distance glasses may be dispensed with and reliance placed on the reading glasses, to which very few persons will object. In some stubborn cases it may become necessary to in- voke the services of a physician, and place the eyes under the influence of atropine, which may need to be continued for several weeks before the spasm is overcome and the ciliary muscle completely paralyzed. Then the exact condition of the refraction can be determined, and if hypermetropic, as it often is, the correcting convex glasses should be prescribed at once and the patient directed to wear them and become accustomed to them while the muscle is recovering from the eflfects of the drug. SYMPTOMS OF MYOPIA. The two principal symptoms are the impairment of dis- tant vision and the improvement of close vision. The eyes are usually large, full and prominent, and the pupils dilated, although as age creeps on they gradually contract, thus diminishing the circles of diffusion and slightly improving vision. 1 he young myope makes use of the same principle to assist vision by half-closing his lids, which habit indeed is so characteristic of this defect as to give occasion for its name, the word myopia originating from two Greek words, meaning "to close the eyes." On account of the impairment of distant vision, myopes are inclined to avoid out-door sports, and rather prefer in- door amusements, as reading, drawing, etc., which do not re- quire good vision at a distance. But, unfortunately, such habits cause congestion of the eyes, and thus favor the in- crease of myopia. Of course, where the correcting glasses are worn early in life, the boy has his range of vision widened. and in this respect is placed on an equality with his com- 150 MYOPIA, panions, and then he lias tlic same desire as they to join in all their games. In progressive forms of myopia the field of vision may be limited and besides show numerous blank spots, on account of patches of retinal atrophy. In some cases of myopia there may be evidences of con- siderable irritation of the eyes, especially after using- them by artificial light for any great length of time. The conjunctiva may be blood-shot and the lids red, while the patient com- plains of pain, sensitiveness to light, a feeling of eye-strain, eye-balls sore to the touch, and the annoying "muscae voli- tantes," which have already been described. The symptoms of myopia that have been enumerated are both subjective and objective, the former depending on the visual sensations of the patient, and the latter on what the optician himself observes. PREVENTION OF MYOPIA. The importance of the prevention of myopia cannot be too forcibly impressed upon parents, teachers and school directors, in order that the conditions which cause it may be understood and removed. This is an age of prevention rather than cure. Everywhere efforts are made to prevent disease and all questions pertaining to hygiene and sanitary reform receive the closest study and attention. The prevention of small-pox, diphtheria, yellow fever, cholera and tuberculosis is enforced by law, and is facilitated by laboratory work with the microscope and test tube. This certainly shows the un- selfish interest physicians manifest in the welfare of mankind, because it is evident that the existence of disease is more profit- able to the medical profession than its absence; but the dis- covery of a prophylactic measure affords more satisfaction to a physician than a new method of cure. The optical profession should measure up to the same standard, and should exhibit the same commendable spirit in developing measures of hygienic reform as it pertains to the eye, and in educating the public along the same lines. The scope of this book will not permit an extended reference to this subject or a complete description of the work that has MYOPIA. 1-'>1 been and should be done in this field, but a brief mention of some of the practical points bearing on the prevention of myopia is at least necessary. Consideration must be given to those conditions of school life which tend to develop this defect; and the first thought that arises is that children should not be sent to school unless their general health is robust enough to endure the strain. In addition, the refraction of the eye should be examined, as well to detect any possible defect as to determine their capac- ity for the work on which the child is just entering. The im- portance of this latter procedure as a prophylactic measure will commend itself at once to those interested in the welfare of children's eyes. LIGIITIXC, OF SCHOOL ROOMS. The school building should be lighted sufficiently and properly, and should also be so constructed as to aflford the pupils all the advantages possible in the way of location, ven- tilation, sanitary plumbing, pure and abundant water, etc. The light in the school room should be direct, and not re- flected from the walls of adjoining buildings. Light that is insufficient or ill-arranged is the most poten- tial factor in the causation of myopia in the sch(X)l room, because such light compels a lessening of the distance between the eye and the book when reading or writing, and therefore the question of proper light becomes an all-important one. The light should be sufficient in quantity, should come from above the level of the eyes, and as far as possible, should fall upon the desk from the left-hand side. This arrangement of light could be best secured if the school rooms were of an oblong shape, all the windows located in one of the long sides, the desks placed in rows at right angles to this wall, and the scholars facing that end of the room which allows the light to fall from the left. The windows should extend upward to the ceiling, starting about four feet from the floor. The total window surface should be (^ne-fifth of the floor area, with the panes as large as possible. It would be better if the education of children could be carried on entirely by daylight, but in cloudy weather, in the afternoons of the short days in mid-winter, and in ni^ht schools, artificial illumination becomes a necessity. The usual naked gas jets are mentioned only to be condemned. The im- proved Welsbach burners afford an excellent liqht. and if properly placed over the children's heails and in sufficient numbers, would constitute a satisfactory metho3 desk as unnecessary, clainiin.q- that the edg^c of desk and of seat should be on same plane. The seats should have comfortable backs, corresiX)nding in size to the heig^ht of pupil. They must not be too high. Showing the improper position assumed by the pupil because the seat and desk is too low, and the edge of the desk is too far in front of the seat. The child Is compelled to sit on the front of the seat, the body falls forward and finds support upon the elbows, which rest upon the desk. In writing, the left arm is used for support while the right hand is employed, which causes the vertebral column to be partially turned upon its long axis and the body to be placed in a distorted position. The head falls forward toward the work and turns to the right; this brings the face too near to the page, the left eye closer than the right. The normal relation between the plane of the face and the work is thus disturbed, while the abnormal near point adds greatly to the strain upon the ac- commodation and convergence. coming- only far enough to support the shoulders and leave the head free to assume the proper position. The top of the desk must be just high enough to allow the elbow to rest upon it without displacing the natural position of the shoulder. 154 MYOPIA. In order to meet all the requirements, it is evident that the size of the desk and seat should correspond to the size of the pupil. But it is equally obvious that a desk rigidly con- structed for all the pupils of a certain grade or a certain age. Showing the correct position \\hich the student should assume, the lower part of back and pelvis being supported by the forward curve in the bade of the seat. The forearm of the pupil rests lightly upon the desk, which is not so high as to raise the shoulders, but sufficiently high to avoid the neces- sity of stooping in order to reach it. Both the desk and seat are adjustable in height by means of the nuts on the pedestal of each. The front edge of the seat projects an inch or two under the desk, which allows the correct upright sitting posture to be assumed and maintained, and in fact the child finds it easier to sit in this position than in any other he can assume. would fall short of answering the purpose on account of ex- tremes in size which may exist. Therefore it is not only necessary to have desks and seats of different sizes for the various grades, but they should also be easily adjustable to MYOPIA. 155 meet the requirements of each pupil in tliat particular grade. After the seat and desk has been adapted to the length of the leg and height of body the adjustment must be fixed by a key which should be in the hands of the teacher, so as not to allow of any alteration by the pupil himself. INCLINATION OF TOP OF DESK. The reasons given why the top of the desk should slope are so interesting and important from a physiological and hygienic standpoint for the benefit of adults as well as children, that the optician should not be lacking in the knowledge which is therein implied. The eyes are moved in dilYerent directions by six muscles. The movements of the two eyes are associated, and only cer- tain sets of muscles of both eyes can be brought into simul- taneous action. For instance, we cannot turn one eye up and the other down, but we can only move both eyes at the same time in the same direction, either up or down. We can use both internal recti muscles in the act of convergence, but we cannot use the two external recti muscles and turn the eyes from parallelism to divergence. We can use the internal rectus muscle of one eye with the external rectus of the other, as when the eyes are turned to the right or left. Of the various combinations of muscles, some can be comfortably kept in action for a length ol time, others only for a few seconds. Thus it requires considerable effort to con- verge the eyes and look upward at the same time; wliile, on the other hand, we can converge and look downward with ease. If we want to see distinctly a line or a plane, instead of a point, a particular turning of both retinae is necesary for each position of the object. When this turning can be produced by a com- bination of muscles which can be effected with case for a length of time, then we can look at the object steadily and ci:)ni- fortably. Therefore the proper position of the book in reading does not depend on chance, but is a physiological necessity. If it is constantly disregarded the eyes become fatigued and a con- dition of asthenopia may intervene. This is the reason why it is so tiring to look at those pictures in a gallery which are 156 MYOI'IA. hung- high on the wall, while the same number of pictures can be examined without fatigue if placed on easels below the level of the eyes. Likewise it is hurtful to the eyes to read while lying down, and if this pernicious habit is persisted in will sooner or later ])nuluce a painful and weak condition of the eyes. Conse(|uentIy, if we want to look for any length of tinu- at any plane surface, as for instance, the page of a ])ook. it is necessary to place it and hold it in such a position as to form an angle of about 45° with the horizon, and then direct the axis of vision of our eyes downward at an equal ang-le of 45°, so that a right ang-le will be formed by their intersection, or in other words, that the visual axis may be perpendicular to the surface of the book. This is the ideal position for the book and eyes in reading, and if the reader will look around him he will see how many persons disregard these plainly proven propositions. For writing, the same inclination for the paper would be equally advantageous, but for obvious reasons this would scarcely be practicable, and for this purpose a less angle is recommended, usually about 20°. It is possible to have a desk so constructed that the inclination of its top might be changed by a simple mechanism. It is obvious that a flat-top desk not only prevents the direction of the visual axis at that angle most favorable to the natural and easy movement of the eye-ball, but also encourages a stooping position with its attendant evils of close sight and gravitation of blood to the eyes. The influence of school life upon the figure of the child and in the causation of curvature of the spine, as well as the disastrous effects that crooked and stooping positions at school may have upon the heart and lungs and abdominal organs, are important matters for serious consideration, but it is not in place to discuss them here, as they are beyond the scope of this work. BLACKBOARDS AND MAPS. Attention should also be given to the distance and location of blackboards, as an important factor in the hygiene of school vision. Tliey should not be placed so far away from any scholar as to necessitate a strain in order to see the marks MYOPIA. ^^' upon their surfaces, but those pupils who have dekctive vision should be LHven front seats near the board. No blackboard should ever be placed between two windows, as the scholar could not see the writing upon it without subjecting his eyes to the irritating glare of light which enters the eye from an im- proper direction, while the board remains in shadow; but the light should be so arranged as to illuminate the board without causing its rays to be reflected in such a manner as to obscure the characters that are inscribed thereon. Some authorities have recommended, as a desirable sub- stitute, white surfaces with black crayons, on the presumption that black marks on a white background can be seen at a greater distance. But on the other hand, the reflection from a large extent of white surface is more apt to be annoying and irritating to the eye than is the same amount of black surface, and therefore we think the old form of blackboard and white crayon cannot be improved upon. For similar reasons, the writer has been using in his offtce for determining the acute- ness of vision and measuring the refraction, a black card with white block letters upon it, and finds it very satisfactory. THE TYPE OF TEXT-BOOKS. The size and form of the type used in school books are of great importance from a hygienic standpoint. All authorities agree that the Latin letters are the best for all kinds of reading. The crooked zig-zag lines of the German letters are by com- mon consent considered very trying to the eyes, and hence that form of letters should never be employed in text-books. It is altogether likely that this type, in connection with the studious habits of the German nation, are responsible for the larger percentage of myopia in that country, in speaking of which an author says, "it is certain that if Germany would absolve itself from nationalism sufficiently to declare an eman- cipation from its miserable type, there would be less myopia among its people." The normal acuity of vision is based upon the ability to distinguish letters which subtend an angle of five minutes, but it would be very unreasonable to expect the eyes to keep at a task for any great length of time which called forth their 158 MYOPIA. Utmost endeavor. This will become evident to any one who compares the strain and effort to read small (diamond) type, with the ease and comfort with which a larger type (long primer) is read, and the latter (the size in which this article is set) is the smallest which should be allowed in school books, or for that matter in any book intended for general reading. The distance between the lines has much to do with the legibility of the page and with the ease with which it is read. When the lines are crow^ded as closely together as the type will permit, the page has a dark and unattractive appearance, and the labor of reading is relatively increased, as is evident to any one who will compare a closely set page of reading matter with one that is liberally leaded. The fact is, a proper spacing be- tween the lines is really of more importance than the size and height of the letters, and the weight of opinion is that this space should not be less than two and a half millimeters, or one- tenth of an inch. The printing should be well done, so that the letters show up clear and distinct. If a large edition of a book is issued, those first run off are clearest, and later on the print begins to appear somewhat blurred and defective. As soon as this is noticeable the type (or electrotype which is gen- erally used) should be rejected and new metal demanded. The paper should be of good quality, as otherwise the beneficial effect of large type properly spaced would be neu- tralized. It should be reasonably thick and opaque, so that the impression of the type on the opposite side should not show through. The surface of the paper should be dulled, so that there may be no unpleasant reflection from it, and of a cream tint. PROPER PENMANSHIP. We do not propose to go very deeply into the considera- tion of the question of vertical or slanting handwriting, but some mention of it is due on account of the agitation of the subject at the present day. There appears to be a growing sentiment in favor of the erect system, because the slanting- form seems to favor an unnatural position of the body and of the paper, and thus tend to the development of myopia. But if the desk and seat are of the proper proportions, and the pupil rightly seated with the paper in a central position in front of 159 is im- him, the question of the selection of the kind of script material from tlie standpoint of the hygiene of vision, which is the only point in whicii we, as opticians, are interested. HOURS OF STUDY. Young children should not be expected to use their eyes more than a few hours each day; all their work should be done in the school room, and when they leave it their minds and bodies should be free from any set tasks. As the child in- creases in years and advances into the higher grades, some amount of study is necessary out of school, and it seems pos- sible that more harm may be done to the eyes by indiscretion in the home work than in school hours. Children are usually under less discipline at home than at school; they are often allowed to read what, when and how they please; no provision is made for proper desks, seats or light; the child assumes various positions and often reads while reclining, with light that is perhaps insufficient or coming from a wrong direction. As a rule, children are sent to school too early in life ; in many instances because the mother wishes to be rid of the annoyance of the child for a few hours each day, and because the law allows it. Seven years of age is young enough for a child to enter school, although six years is the legal age; but really such an important matter cannot be regulated by statute, but should depend on the physical condition of each individual child. PREVENTIVE MEASURES. In the prevention of the development of myopia in chil- dren, the importance of giving to the child for his playthings objects of considerable size becomes evident. Small ones, books with fine print and games with minute figures, all im- pose a tax upon the accommodation and should be avoided. On the other hand, out-door plays should be encouraged, be- cause they do not require any close vision, or at least all play objects should be sufficiently large not to require any effort of accommodation. After the child enters school he should not be required to keep his eyes uninterruptedly upon the book, as some teachers with mistaken zeal insist upon, under penalty of receiving a bad mark for misconduct, but he should rather IGO MY(,)PIA. be encouraged to rest liis eyes and relieve their fatigue by looking- up from his books and glancing around at more dis- tant objects. Frequent interruption of any kind of confining work is essential to symmetrical development and the maintenance of a healthy condition of the body, and this is especially true of the young. If one attempts to hold up an object at arm's length, and thus imposes a continued effort upon these muscles, a feeling of strain and exhaustion soon becomes ap- parent, and the act must be quickly discontinued; and yet the muscles of the eyes are often forced to do similar work: is it any wonder then that myopia results? Myopia is seldom congenital, although it may be heredi- tary and appear soon after birth. It rarely develops, however, before the eighth year of life, more often the tenth, and reaches its maximum about the ag-e of twenty. Where an inherited predisposition to myopia exists, the child should be kept out of the school room as long as possible ; perhaps until he is ten or eleven years old. In the meantime, and in fact all through life, open-air sports should be encouraged, with gymnastic exercises for the development of the body and perhaps an in- termixture of properly assigned manual labor. The fact should be impressed upon the minds of parents and edticators that it is better to devote the years of youth to laying the foundation of a healthy constitution and strong eyes than to encourage forced intellectual advancement at the ex- pense of feeble health and impaired vision. The moral of this advice is emphasized by the country boy, raised upon the farm and receiving but few educational advantages, who so often outstrips his city cousin, whose life from four years of age has been spent in kindergartens and graded schools. For those predisposed to myopia, mental education should be always subject to the physical condition, and earnest, systematic study should not be commenced until the sixteenth year, when the body is stronger and the coats of the eye firmer and better able to resist the encroachments of myopia. Even then it w^ould be better if the child could be taught privately, instead of being placed in the general class and expected to keep pace with his normal-sighted companions. MYOPIA. Ifil In order to prevent the onset of myopia, or its increase, the stooping position and a close approximation of the book, which taxes both accommodation and convergence, must be avoided; the patient should be instructed never to read in a moving car or carriage, where the continual jarring requires a constant change in the accommodation; not to continue close vision too long at a time without suitable periods of inter- mission: to maintain a reading, writing or working distance of at least twelve inches, and more if {x^ssible; tO' select books and newspapers printed in clear, large type; to avoid fine sewing and tedious fancy work; to write a large hand (as myopes are especially prone to small writing) ; to see that daylight is suf- ficient in quantity and coming from the proper direction; not to use the eyes by artificial light, or as little as possible; and if symptoms of irritation become manifest, or there is a marked increase in the myopia, to give the eyes complete rest. TESTS FOR MYOPIA. In myopia the distant vision is impaired, while the close vision remains fairly good, and therefore if a person is unable to make out the large letters on the test card, hanging twenty feet distant, but can easily read the small print six or seven inches away, it is fair to presume he is myopic. This is a rough test, but it is one of value, and can be made at any time and under any circumstances and without any outfit. An ordinary newspaper can be made to suffice, the letters of the title line forming the distance test and the small type the near test. Of course, if with the impairment of distant sight near vision is also defective or imposible, there is something more than myopia; perhaps amblyopia, or some diseased condition. The differential diagnosis between myopia (which is cor- rectible with glasses) and an organic disease (which is beyond the reach of optical help) can be quickly made by means of the pin-hole test, which has been described and illustrated on pages in The Optician's Manual. Tlie trial case contains one or two of these pin-hole disks, made of hard rubber and mounted in a metal ring with handle; but in the absence of a test case, a card or a stifT piece of paper can be punctured with a pin; an equally efficacious pin-hole test is at hand, and one '••■- MYOPIA. that can he iiK'uk' and used in any lonely cahin in the hack- woods. The principal tests for niyoi)ia are: 1. Trial case and test types. 2. Ophthalmoscope. 3. Rctinoscopc. 4. Refractometer, optometer, prisoptometer. 5. Scheiner's method. 6. Chromatic test. TEST WITH TRIAL LENSES. The patient is seated facing the test card of Snellen, which is well illuminated and hanging twenty feet away. The trial frame is placed on his face and carefully adjusted for height of nose and pupillary distance. Both eyes should be kept open, but only one eye should be tested at a time, the other being excluded from vision by a solid rubber disk being placed in the trial frame over it. The left eye being thus covered, the patient is asked to name the letters on the lowest line which is legible to him. If he reads the No. 20 line, that is if his visual acuteness is f^, the eye is presumably emmetropic, although latent hyperme- tropia may be present. If he reads the line hesitatingly and makes some mistakes in naming the letters, there is prob- ably some astigmatic element in the case. But either of the above conditions precludes the existence of myopia, which cannot be present if the vision is wholly or even partly fi}, because this defect markedly impairs the acuteness of vision. If, however, the patient cannot distinguish any letters on the Xo. 20 line, and perhaps cannot even read the 30 or 40 lines, we may infer the possibility of myopia; but first in order to prevent error, convex glasses must be tried in order to detect any hypermetropia. If they are immediately and posi- tively rejected, it is then proper to begin to suspect myopia, and we ask the patient to take the line near type (which a myope is easily able to read) and move it away from him to the greatest possible distance from the eye at which it can still be seen distinctly. The distance from the eye to the type M^'()IM.\. 103 is then carefully measured, which, when converted into diop- trics, will represent (at least approximately) the degree of myopia, and the corresponding concave lens will be the proper correction. This glass is placed in the trial frame in front of the eye and the distant vision is again tested. The strength of the lens is diminished or increased, if necessary, until the maximum acuity of vision is obtained, always reineiuhering to give the preference to the weakest glass. The other e}C is then similarly tested, and when both eyes are corrected an effort should be made to reduce the strength of the glasses by placing weak convex lenses in front of them. If any glass above + .50 D. is thus accepted, the examiner's suspicions should be aroused as to the possi- ble existence of spasm of accommodation. Otherwise the lenses may be considered as correct. A recent book says: "Take in your hand a + .50 D. S. and a — -50 D. S., trying first one and then the other before the eye you are testing. Whichever lens gives the best vision, after a careful trial, will be an indication of what kind of lenses (convex or concave) the patient is going to need." Now we are compelled to take issue with the author of this work, as we cannot consider such a method of testing as proper. It is a well-known fact that a weak concave lens will be accepted for distance by almost any eye, even by emme- tropic and hypermetropic eyes, and in slight degrees of the latter defect will be preferred to weak convex. Therefore when weak plus and minus lenses are tried alternately, the patient will most likely select the concave, or else he will be confused and will be unable to decide between them. Tlie writer feels that he can make the positive statement that in such a method of testing the convex lens would never be chosen ; this makes the test entirely one-sided and robs it of its value. The advice given on these pages has always been to com- mence the test with convex lenses, and if they are accepted at all, not to confuse the patient or run the risk of error by trying concaves, and this advice is especially applicable in cases where the vision is fSy or nearly so. Where the vision is markedlv below normal, the rule still holds good to begin the lG-4 MVoriA. examination with convex lenses, and only in case of their posi- tive rejection is it proper to try concaves. After these preliminaries, suppose — .50 D. lens quickly and unmistakably improves vision on the test card, it is prob- able the case is one of myopia and needs concave lenses. Tlien the — .50 D. is removed and a — .75 D. is substituted for it. with a still g-reatcr improvement in vision, which possibly may now reach the normal standard of f ^ , in which case this lens would be the measure of the defect. If not, a — i D. is next tried, and as long as a further improvement in vision is obtained, the lenses are gradually increased in strength a .25 D. at a time until the best vision is secured that it is possible This diagram shows the path of the rays and the position of the image. The rays issue from the myopic eye convergently and focus ten inches in front of it; they then cross and enter the emmetropic eye and are united upon its retina. to get with concave spherical glasses, always remembering that the w^eakest glass is the one to be preferred. This lens is then placed in the back groove of the trial frame and the rubber disk slipped in front of it, and a similar test made of the other eye. After the second eye has been carefully measured, the rubber disk is removed from before the first eye and the patient can see with his both eyes to- gether, each properly corrected as far as can be with spherical lenses. The frequent change of lenses in the trial frame is more or less confusing to the patient, and should be avoided as much as possible. Hence in high degrees of defect, instead of increasing .25 D. at a time, it is better to jump .50 D., or even i D., until something near the normal acuteness of vision is reached, and then proceed more cautiously and with shorter steps. When lenses are found that afford pretty fair vision. MVOPIA. 1G5 instead of removing the lens and replacing- it with another, its strength may be increased or decreased by holding before it alternately a — .25 D. and a + .25 D. If with the convex lens vision remains as good, then the concave lens in the frame is stronger than is necessary, and should be reduced a quarter of a dioptric. If on the other hand the — .25 D. produces a marked improvement in vision, then the lens in the frame is not quite strong enough, and should be replaced by one a quarter of a dioptric stronger. NORMAL VISIOX NOT ALWAYS POSSIBLE IN HIGH MYOPIA. If with the lenses found according to the above methods the patient, at twenty feet, can read the No. 20 line clearly and distinctly, it is right to assume that the full defect has been measured and the proper correcting lenses found. Even if the vision is less than |^, with these glasses it does not prove they are incorrect ; it simply shows this is the best vision attainable with concave spherical lenses. In high degrees of myopia it is an unfortunate fact that vision cannot be raised to normal by any glass, and this may perhaps be comforting knowledge to some conscientious opticians who have vainly endeavored to tind some glass that would aflford a vision of-j^. There are two reasons for this — the impaired sensibility of the retina and the diminishing effect of concave lenses. Either one of these would be suf- ficient to account for the lessened vision, while the two to- gether only serve to make it more pronounced. In extreme cases of myopia there is great bulging of the fundus and stretching of all the coats of the eye, in which process the retina is the membrane that suffers the most, its layer of rods and cones being separated and fewer of them being impressed by the image formed, and therefore the degree of vision would be lessened. The function of a con- cave lens is to minify, and the diminution of an image by strong minus lenses is very marked, and hence such a glass, by reducing the image formed, would tend to impair the acute- ness of vision very perceptibly. When these two causes act together and an image s;iialler than normal is received by a less number of rods and cones than natural, the wonder ](!(') MYOPIA. rcalh- is that the xisioii is as suscej)til)lc of as iiuich iniprove- inent as it is. TEST WITH OrilTII.M.MOSCOrE. In emnictropia parallel rays are brought to a focus ex- actly on the retina and, therefore inasmuch as the retina is located precisely at the principal focus, the divergent rays proceeding from it (after being acted on by the refracting media of the eye) would emerge from the cornea parallel. In myopia, on the other hand, the retina is placed beyond the principal focus and parallel rays unite and cross over be- fore reaching it. Under such conditions the rays proceeding from the retina would emerge from the eye convergent and would meet at this far point. When looking into an emmetropic eye with an ophthal- moscope, the observer must approach within two or three inches in order to see the details of the fundus clearly. In myopia, on the contrary, nothing can be clearly seen at such a close distance with the naked eye, but on withdrawing the instrument from fifteen to twenty inches, the optic disk and blood-vessels will gradually come more or less clearly into view. In a case of myopia of 4 D. the rays reflected from the retina would converge and meet at a distance of ten inches from the eye and form there an inverted image, which can be clearly seen by the optician, at his ordinary distance for small objects (say from ten to twelve inches), by calling into action his accommodation and adjusting his eye for that par- ticular spot at which the aerial image is formed. In this case, where the image is at ten inches and the observer's eye ten inches from that, it will be found that a distance of twenty inches will be the proper one to assume. The precaution must be taken not to approach the image too close — that is, the optician must always keep beyond his own near point, else his accommodation will not suf^ce to afTord him a distinct view. That this image is inverted is proven by the fact that when the observer moves his head slightly from side to side the image moves in the opposite direction, hence a contrary movement of the image, when the ophthalmoscope is held MVdPlA. 167 some little distance away, is one of the diagnostic tests for myopia. Direct Method. — Inasmuch as the emergent rays from a myopic eye are convergent, it is evident that such converg- ing- rays cannot be focused upon the retina of an emmetropic observer, and hence an erect image of the myopic fimdus is impossible without the aid of a concave lens to lessen their convergence. The rule then in simple m\opia is to ascertain the weakest concave lens that will render the fundus clear and distinct as being the approximate measure of the defect. After a few trials it is easy to decide which concave lens, rotated into the sight hole of the instrument, will afford the clearest image. The accuracy of this method (the direct method of the ophthalmoscope) presumes the corneae of observer and patient to be in actual contact, but as that is impossible, the distance between them should be added to the focal length of the lens found as above. For instance, by referring to the illustration (page 164) the rays are seen to cross ten inches from the myopic eye. Sup- pose the observer placed his eye one inch in front of it, then the position of the focus is nine inches back of his cornea, and therefore a — 4.50 D. lens in the aperture of the ophthalmo- scope would render the rays parallel and allow thetn to be focused on his retina without any efifort of accommodation. But as is evident from the illustration, this — 4.50 I), lens is more than the full measure of the defect: but by adding the distance between the eyes of patient and observer to the focal distance of the lens found as above, the result will be the exact measure of the myopia present in patient's eye (i inch added to 9 inches = 10 inches focal distance, or a refractiv* power of — 4 D.; it being understood that an increase of dis- tance represents less optical defect). Tlie rule then is that the weakest concave lens that renders the details of the fundus clear and distinct will be the extent of the myopia. Suppose when the optician looks into an eye through the aperture of his ophthalmoscoi>e everything about the fundus appears blurred and indistinct; a convex lens is then rotated into the sight hole, with the etTect of making it IGS MYOPIA. worse; now the weakest concave lens is tried, and at once the fundus begins to look clearer; then another and another i^s used, until finally all the details of the eye-ground arc brought out distinctly, and this lens will approximately represent the degree of the myopia. It should always be remembered that preference is to be given to weakest concave lens that renders the fundus distinct. SKLF-RELAXATIOK OF THE ACCOMMODATION. In attempting to determine the amount of myopia by the direct method of the ophthalmoscope, the accommodation of both observer and patient is supposed to be at rest, and upon this fact rests the accuracy of this method. Otherwise a con- dition of false myopia is temporarily produced by the invol- untary use of the ciliary muscle in either optician or patient, which would require a concave lens to enable the details of the fundus to be clearly seen. This is an error into which many beginners fall, thinking they have a case of myopia to deal with, because a concave lens brings out the blood-vessels and optic disk more shai"ply, w^iereas it may be emmetropic or even hypermetropia metamorphosed by the accommodation. The patient's accommodation is encouraged to relax by the dark room, and by requesting him to direct his eyes to a distance, without however attempting to fix the vision on any particular object. But it is not so easy for the optician to relax his power of accommodation, because he is inclined, naturally, to look at the fundus of the patient's eye as at a near point; whereas it should be viewed as if at infinite distance with a relaxed ciliary muscle. The faculty of placing the ciliar}- muscle at rest is one that can be acquired by the optician, in the practice of which the following exercises have been recommended as facilitating' that end. 1. The optician directs his eyes toward the ceiling, and while in that position holds above them a sheet of white paper upon which there is a black ink spot. When he notices that the spot appears double, the paper and the eyes are to be slowly lowered and the endeavor made to keep the gaze directed into distance and the accommodation at rest, in which case the dot MYOPIA. 169 will continue to appear double, even when it is below the level of the eyes. It is comparatively easy to get the double vision when the spot is high up over the eyes, but the difficulty in- creases as the object is lowered to the level of or below the eyes. 2. The finger or a pencil should be held ten or twelve inches in front of the, face, and as long as the gaze is kept at a distance and the accommodation remains quiescent, the ob- ject will appear double. 3. While reading a book or card of fine print, held quite close to the eyes, the optician attempts to look through and beyond the book or card, as it were, when the lack of accom- modation will cause the letters to run together and become blurred. At the same time the convergence can be felt to lessen and the eyes to assume a parallel condition. By a frequent repetition of these exercises, the optician can learn to bring an object close to the eyes without bringing into play his accommodation or convergence, and with the accommodation thus under his control, he is in a position tcj obtain the most accurate results in the estimation of the amount of myopia by the direct method of the ophthalmo- scope, which, however, should always be verified by the sul)- jective examination. 1X1)1 KIXT METHOD OF OPHTHALMOSCOPE. By the indirect method the eye is viewed at a distance of twelve to fifteen inches (usual reading distance) through a strong convex lens held at its focal distance from the patient's eye. An inverted image of the optic disk and blood-vessels is seen, which is sharper but smaller than by the direct method. In myopia this inverted image of the disk is smaller than in enunetropia, but increases in size as the strong convex lens is withdrawn from the patient's eye. While the indirect method gives a larger field, and thus favors a more rapid examination of the whole fundus, yet for determining the refraction of an eye the direct method is much to be preferred, and besides it is not so difficult for the beginner to learn. 170 TKST WITH KKTlXOSCOrE. The essentials for the rctinoscope test, with full instruc- tions as to how it should be conducted, were described in the chapter on "Hypennetropia." When the shadow in the pupil moves in an opposite direction to the light on the face, the eye is known to be myopic (the plane mirror being- used), and con- cave spherical lenses are placed in the trial frame until the weakest glass is found which reverses the movement of shadow and makes it travel in the same direction as the light on the face. This is the correcting lens at the distance at which the examination is conducted, to which must l)e added the lens representing that distance ( — i D.). Suppose, for example, the far point of the myopic eye is at ten inches, and if the eye was examined at a (Hstance of twenty feet a concave lens of 4 D. would render the rays of light parallel and stop all retinal reflex. But as the examina- tion is conducted at a distance of only one metre or forty inches, a lens of — 3D. will be sufficient to halt the reflex; and, therefore, in estimating the total amount of myopia,, i D. must be added. TESTS WITH INSTRUMENTS. Rcfractomctcr. — As the patient loo'ks through this instru- ment at the test card, hanging fifteen or twenty feet away, any desired number of convex or concave lens can be placed before his eye by simply rotating a wheel on the side of the tube, which is marked in dioptrics and fractions thereof, and num- bered in red and white to distinguish between convex and con- cave. The revolving dial is first placed at the zero mark, so that no focus whatever, either spherical or cylindrical, may be before the e}'e at the time the test is begun. The patient is asked to name the lowest letters which are visible on the card. In myopia he will be able to see only the largest letters, or in high degrees none at all. As a matter of precaution, the wheel is turned toward convex lenses, which at once throws a deeper blur over the card and letters. Then the rotation is made toward concaves, with the effect of brightening and clearing the card, and the degree of myopia is estimated by reading the 171 graduation on tlic indicator after the focusing adjustment had been turned as far to the right as necessary to make the small letters clear and distinct, and then back a little, if possible, without casting a blur upon them. The most imjx)rtant point, and one to be kept constantly in mind when dealing with myopia, is to obtain the best vision with the instrument so ad- justed that it registers the very smallest amount of defect, and to prescribe accordingly the weakest glass. The Refractometeh. Optoiiidcr. — This instrument consists of an adjustable stand supporting a horizontal rod, which has two movable slides for holding lenses, with a test card at the far end and an eye shield at the near end. To measure the amount of myopia, a concave lens of 8 D. is placed in the clip of the eye shield and a convex lens of the same strength placed in the slide and moved away from the eye. The patient looks at the small test card, and the point where the type appears brightest will in- dicate the proper correctiiig lens, as shown by the scale marked on the rod. Pfisoptoiiu'lcr. — This iiistnimeiit rMiuains a doul^lc ])risni. set in a large disk, which can be revolved from o to in its own merits. Many myopes wear their full correction constantly, both for near and distance, without '^nffering anv inconveni- 178 MvoriA. eiioe ami apiiarcnily without any injur\- to their eves, while others can scarcely hear their correction for distance much less for reading". While the writer was penning- these lines a patient con- sulted him, thirty-five years of age and wearing — 6.50 D. glasses. Has worn these same glases for twenty-three years, usin,g them for all purposes, near and far, and without any difficulty. Recently has suffered from headache, which he at- tributes to an attack of la grippe, but his physician advised him to ct)nsult an oculist. On examination 1 was surprised to find a myopia of onl\- 5 1). in R. li. and 4 D. in L. E. The remarkable point about this case is that his glasses should have been so comfortable for close work all these years, in spite of the fact that this defect was over-corrected (thus rendering- his eyes really hypermetropic) and that he was approaching- the time of life when a lessened accommodation would call for a weaker concave lens. DOXDEKS" .\1)V1C1-:. In discussing- the importance of the proper selection of glasses in individual cases of myo]>ia. Bonders' remarks are so apropos that they are worthy of re])roduction on these pages, and especially as everything issuing from the mouth or pen of this gifted man is universally accepted as gospel truth by all seekers after optical knowledge, alike by oculists and opticians. He savs: "The prescribing of spectacles for mv- opes is a matter of great importance. While emmetropic and hypermetropic eyes do not readily experience any injury from the use of unsuitable glasses, this may in myopes, particularly on account of the morbidly distended condition of the eye-ball and of the tendency to get worse, be very dangerous. There exists in general a dread of the use of too strong glasses. It is laid dowai as a rule: Rather too w^eak, or no glasses, than too strong. In this rule the necessary distinction is lost sight of. Too strong glasses make hypermetropic eyes myopic, and my- opic eyes hypermetropic. The rule therefore cannot be equally true for both. In fact it is in general much less in- jurious to produce a certain degree of mvopia than of hvper- MVOPIA. 179 nietroi)ia, in which last particularly much is reciuired of the accommodative power. Jhe rule would therefore be more correctly stated thus: in hypermetropia we must beware of ^ivino- too weak; in myopia of Skiving- too strong- glasses; a ndc the second part of which we should especially insist upon. l')Ut even by this little is gained. Xot using glasses, or using too weak glasses, may also be injurious to myopes. All the circumstances must therefore be studied, which can exercise an influence on the choice of glasses. It is difificidt to reduce these to definite rules."' A PERSONAL EXPERIK.VCK WITH CONCAVE GLASSES. M. Sarcy. a well-known h'rench critic, had congenital myopia, and in later life became temporarily blind. In one eye he suffered a retinal detachment, and in the other a cata- ract. By means of an operation vision in the latter eye was restored and became better than ever. He relates an inter- esting bit of personal experience in the following words: "I was born near-sighted; nian\- physicians assert that persons are never born near-sighted, and only become so. Science may say what it pleases; T was born myopic. One day, prompted by a spirit of mischief, I got hold of the big silver spectacles which my father wore and clapped them on. Fifty years have passed since then, but the sensation I experienced is keen and thrilling to this day. I gave a cry of astonishment and joy. Up to that moment I had seen the leafy dome above me only as a thick green cloth, through which no ray of sunshine ever fell; now, oh wonder and de- light! I saw that in this dome were many little brilliant chinks; that it was made of myriad separate and distinct leaves, through whose interstices the sunlight sifted, imparting to the greenery a thousand forms of light and shade. I'.ut what amazed me most, what enchanted me so that 1 caimot speak of it to this day without emotion, was that 1 saw suddenly, between the leaves and far, far away beyond them little glimpses of the bright, blue sky. I clapped my haiuls in ecstasy and was mad with astonishment and delight." 180 HOW MVOriA DISTURBS THE NORMAL RELATION EXISTING BE- TWEEN ACCOMMODATION AND CONVERGENCE. The far ix)int of a myope is always situated at a finite distance, and is determined by the degree of the defect. A myope of 4 D. has a far point of ten inches, and can see at that distance without any effort of accommodation, but he must converg-e four meter angles in order to maintain binocu- lar vision. Now, in the case of an emmetropic eye the accom- modation and convergence are used in equ^l proportion, and hence a distance of ten inches would call for 4 D. of accom- modation and four meter angles of convergence. Therefore in myopia the convergence is necessarily used in excess of the accommodation, a condition just the reverse of hypermetropia where the accommodation is used in excess of the convergence. Nature will allow to a certain extent the use of one function in excess of the other as a result of nerve education, but she inflicts a penalty for this as shown by the frequency of "eye strain" under these conditions. In myopia the fusion efifort must be greater than in em- metropia, and the greater this effort the more the fatigue of the internal recti muscles; this fatigue leads to "insuf^ciency" of the muscles and thus matters are made worse. A myope requires more convergence of the visual lines because vision takes place so close to the eyes, and this is particularly difificult in this defect on account of the elongated shape of the eye-ball which impedes its movements. There may be no actual weak- ness of the internal recti muscles, but only apparently so on account of the excess of work they are called upon to perform. DIVERGENT STRABISMUS. In the previous chapter it was shown that hypermetropia was the direct cause of a majority of the cases of convergent squint. And as myopia is a condition of the eye exactly the reverse of hypermetropia, it will be found that many of the cases of divergent squint occur in connection with near-sight- edness. The accommodation is used but little, while the con- vergence must be excessive, which latter continues until the eyes have reached the maximum state of convergence, and then the energv and tone of the internal recti muscles sooii MvoriA. 181 become exhausted, and as it tires and gives way the eye turns outward. The power of accommodation still remains unim- paired, but the power of convergence is worn out, because the limit within which the two functions may vary has been over- stepped. As soon as the object is brought nearer than the extreme limit of convergence in binocular vision will permit, divergent strabismus necessarily takes place, and this may occur even if there be no actual insufficiency of the internal recti muscles, just as in hypermetropia there may be no actual weakness of the ciliary muscle; but simply that in each case the muscles have laid upon them work which is beyond their power to perform. While the convergent strabismus of hypermetropia usually makes its appearance in childhood, the divergent squint of myopia is rarely developed until a more advanced age, and is usually connected with the progressive form of the defect. If the myopia develops slowly, the internal recti muscles may gradually increase in size and strength sufficiently to per- form the excessive labor demanded of them, but usually there is a deficiency of power of one or both of these muscles to maintain the required convergence for any length of time, and especially if the progress of the myopia has been rapid. In such cases the internal recti muscles are too weak to resist the action of the external, and the eye rolls outward and double vision results. When once an insufficiency of the internal recti has manifested itself, the muscles do not readily regain their strength even after considerable periods of rest ; they be- come less and less able to sustain prolonged action, until finally the insufficiency becomes so annoying that artificial assistance must be sought or binocular vision abandoned. TREATMENT OF THE MUSCULAR INSUFFICIENCY ACCOMPANYING MYOPIA. Insufficiency of the internal recti muscles is usually found in cases of myopia ranging from 4 D. to 7 D., and when it occurs the advice is at once gratuitously offered by all the friends to rest the eyes, which the patient is inclined to adopt because it affords temporary relief. If these muscles are not 1S2 MvoriA. straineil. naturally they will cease to ache. But. as in the case of all other muscles, if they are not used they undergo loss of tone, and hence the more they are rested the less they will be able to work. Therefore the common prescription of rest is bad. unsoimd in principle and disastrous in practice. The writer has seen cases of this kind who could not use their eyes at all, where reading for only a minute brought on pain and lachrymation. Such persons being debarred from reading and almost every use of the eyes, have nothing to do but to dwell upon their own troubles, and they are constantly worried by the fear they will some day become blind. The proper principle to adopt in the management of these cases is to train and strengthen the muscles by discreet use and by gymnastic exercises. The right lenses for reading are carefully chosen according to the directions already given, and then they must be accorded a patient trial to see how far or how long their use is practicable. By increasing the reading distance these glasses lessen the efifort of convergence, which is thus made more nearly equal with the accommodation. If. however, this method fails to afford the desired relief it may become necessary to combine prisms. In the slighter degrees of myopia, some authorities recom- mend that the glasses should be worn constantly, for the follow- ing reasons: In this way the eyes are practically made emme- tropic; the accommodation is brought into action instead of allowing it to remain idle; there is no occasion to hold the book close, a habit which has much to do in the causation and aggra- vation of myopia. Priestley Smith says: "My present custom is to encourage rather than discourage, with proper limits, the use of the accommodation; in other words, to advise those whjo can to use the same glasses for reading and distance, and where this is impossible, by reason of weak accommodation, still to give reading glasses as strong as can be worn with comfort." The full correction of the myopia restores the harmony between the functions of accommodation and convergence, a procedure which may be quite practical in young persons, but for this very reason in older patients it is not well borne. The habit of converging in excess of accommodation has become MYOPIA. 183 SO fixed for so many years, that it c-aiinot cvi-n l)y practice he easily relaxed, and under sueh eireunistanees if the wearing' of the glasses he insisted u])()n. lhe\ may hecome a cause of eye strain instead of a means for its removal. I'or such persons, if the myo])ia l)e less than 5 1)., the wearing of glasses for distance will he all that is necessary. As a matter of fact there are many persons with a myo|)ia of 3 D. or less, who never use glasses at all; the\- are not incon- venienced hy the ])artial indistinctness of distant vision, which is scarcely marked enough to ])revent the recognition of ordinary-sized ohjects. while their near wDrk can be accom- plished at the usttal distance without any strain upon the eye. Till-: ()Tiii:k sidI': oi- iiii-; (jii-.siiox. Landolt's views are somewhat dilTerent from those given above; he says: ".\ myope must he prohibited from wearing a concave glass for any distance at which he can see clearly without accommodation. Correcting glasses have a very serious disadvantage for the myoi)e, because they force him to make an effort of acconunodation from which his ametropia grants him dispensation, and the\- de])rive him oi another ad- vantage, /. c, of the larger size of the retinal images obtained by the naked eye, and which the glasses make smaller." After all, each case nuist l>e managed on its own merits; on the one hand we must avoid an overtaxing of the accom- modation by a too strong concave lens, and on the other hand we must prevent the strain of excessive convergence, because the stooping position of the head which accompanies it favors congestion and leads to increased intraocular pressure, and thus tends to the increase of the defect. With this view, the concave glasses that lengthen the reading distance to twelve or fifteen inches, j^lay an imp(-)rtaut part in relieving eye strain and jireventing increase of the myopia. MlSl I.K TKSTS. In order to determine the relative or absolute weakness of the internal recti nmscles, a trial should he made to see what strength of prism they are able to overcome. I'or this pur- pose the patient looks at a lighted candle placed at a distance 184 MYOPIA. of twenty fcrt. 'I'licii ;i wi-ak ])risni is placed l)rf( )!■(.' one eve. base out, cansin*^' a nii>nientar\" (liploi)ia. which soon disap- pears. Now a similar prism is placed before the otlier eye, with a like result. This is repeated with increasing- prisms until the double images of the candle llanie can no longer lie united into one by any muscular effort. If it is found the muscles can thus overcome a ])air of prisms of 12° each (makings a total of 24"), they cannot be con- sidered as deficient in strength, and the prismatic element will scarcely need to be added to the necessary concave lenses, the use of which alone may be all that is necessary tO' restore the normal relation between accommodation and convergence, and thus relieve all the eye symptoms. Such use of the eyes may be regarded as gymnastic exercise, to be stopped before it produces undue fatigue, and to be resumed at regular inter- vals. Sometimes there will be a good deal of pain at first, especially with nervous persons and those who have been try- ing the "rest" cure, but they nuist be encouraged to persevere jiotwithstanding. If, however, the internal recti muscles cannot overcome the diplopia caused by a pair of prisms of 12°, bases out, they must then be regarded as absolutely weak, in whicli case it may become necessary to combine prisms in order to assist and strengthen them. In cases of high myoipia (that is, from 6 D. to 20 D.) the eyes are often saved the convergence effort at the expense of binocular vision ; that is to say, the person uses only one eye for vision and the other squints outwardly. If such a con- dition has continued long enough to become a confirmed habit, it is scarcely worth while to attempt to correct it; in fact, it is an almost impossible task to restore binocular vision and cause the two eyes to work in harmony. In many of these cases it will be found on examination that one eye is used chiefly for reading and the other principally for distance, and to make the effort to disturb such an arrangement oftentimes does more harm than good, and here the optician must be content to give the proper glass to each eye for its own particular use. In contrast with the 24° prism, which the eyes can over- come when placed base out, we find that not more than 6' ov 18: 8° can be borne when placed base in. This marked difference is owing to tlie fact that in the first case the internal recti muscles are brought into action, and in the second case the external, and that the former are so nuich stronger than the latter because they need to be used so much more. When it comes to prisms being placed vertically, but very few persons can overcome more than i° or 2°, because the superior and inferior recti muscles are relatively so much weaker than either the internal or external recti. The nomen- clature of, and the tests for, the various muscular anomalies have been described in the chapter on "Method of Examina- tion," to which the reader is referred. A 11 USE OF THE KVES. The eye, like any other organ of the body, and in the same manner as any delicate instrimient. may become the sub- ject of abuse, the bad effects of which are most noticeable during its growing period. The coats of the eye-ball do not reach their full measure of firmness and power of resistance until adult age. about the twentieth year of life, the time when the rest of the body arrives at maturity. Consequently before this age, and particularly between the ages of six and sixteen, during what may be called the school years, the eye is liable to injury from overwork. This 186 MYOPIA. results (as has been stated earlier in the chapter) in the pro- duction of myopia. After the twentieth year of life the eyes nia\ be abused in many ways by overwork and insuflficient or im])roper lio-ln without much danger of causing myopia. One-fourth of the same application of the eyes at the ag^e of ten, with its coats and contents soft and yielding-, would cause the ])osterior wall to give way and bulge and bring about the defect of mvopia. Whereas when the eye is well hardened by full growth a nuicli greater amount of eye application can be borne continuously without the fear of causing the walls of the eye to stretch and injuriously changing the shape of the organ. Hence the fact obtains that the danger of the i)roductit>n of myopia by abuse of the eyes is peculiar to youth and to its growing state. We sometimes meet persons having a slight degree of myopia who are so little inconvenienced by it that they are not conscious of being near-sighted: in fact, consider their vision as up to the normal standard. The existence of the defect may be accidentally discovered by contrast with the sharper sight of some friend, or by casually trying on a pair of concave glasses which happened to be in their w^ay, and which brightened up distant vision to such an extent as they never before believed possible. Others may complain of their near-sightedness, calling attention only to the fact that they are compelled to hold their book very close, but never making mention of their inability to see distant objects. CORRECTION OF MYOPIA. The correction of myopia is by means of concave lenses properly adapted, and the manner in which they act can be readily understood. It will be remembered that in this defect parallel rays of light meet in front of the retina; if now the focus can be thrown back just far enough to correspond ex- actly to the location of the retina, then and only then does clear distant vision become possible. This is accomplished by means of concave lenses, which spread the rays of light and cause them to enter the eye divergently, and then (the refrac- tive power of the eye remaining the same) thy will not meet MvoriA. 187 in focus so soon as the parallel rays; this is equivalent to throw- ing the focus farther back, and if the concave lens corresponds with the degree of myopia the focus will he exactly upon the retinal surface. I'KAC TICAf. I'OIX'IS. In myopia, up to a certain degree, there is usuall\ no dis- turbance of close vision, but when it exceeds 5 1). then there is apt to be some trouble in reading. In the higher degrees there is no distinct vision beyond a few inches from the eyes, and consequently as such a myope cannot fix objects, his eyes assume a peculiar far-away look. In the slighter degrees the only inconvenience suffered is a limitation of distant vision, so that if the ])erson does not wish to wear glasses no very great harm is done, only the loss of pleasure of seeing the world quite as distinctly as other peo- ple see it. The reading limit is not interfered with, as the measure of the myopia (say 2 D.) indicates that the person is able to read as far away as twenty inches, and therefore in these cases there is no occasion to hold the book close, but it may be kept at the usual reading distance where there is no very- great demand made upon either the accommodation or con- vergence. But it is just in this class of cases that the precau- tion should be taken to guard against any inclination to hold the book too close or to read by any kind of insufficient light on account of the imminent danger of increasing the myopia by these means. Floating specks before the eyes, sparks. Hashes of light, white or colored rings, are not uncommon in this defect, and they are apt to cause the patient a great deal of uneasiness; but they arc not usually of any special pathological import. HKXJAMIX FRANKLIN, TIIK OKIC.INAL 1UI-<)CA1. MAN. Tn myopia the effects of presbyopia are not felt at the usual time, perhaps not until the age of fifty-five or sixty ; but when it does manifest itself, there is the double inconvenience of needing glasses for both distance and reading. This annoy- ance would be felt by clergymen, lecturers, and others who might desire to look at the book in their hand one moment, and then to lo«^k at the audietice. some of whom might be at 188 MYoriA. a distance of fifty feet or more. This was the case of Ben- jamin I'Vanklin, and as he was a very busy man and could ni>t aflford to waste so much time as niiglit be required to con- stantly change his glasses if he wore separate pairs for reading- and distance, he had made to his order a pair of spectacles which contained in the one frame both pairs of glasses, known as divided or double focus spectacles, and he was the first to wear this form of spectacles, which are so common at the present daw The eyes should be examined at intervals, perhaps once a year, to determine tBe degree of myopia, so that if there is any tendency to an increase of the defect, it may be at once detected. Spectacles should be worn for distance, or for dis- tance and reading as may be indicated, with the proviso that the book be kept well away from the eyes, not allowing it to get any nearer than eighteen inches, except in aggravated cases where such a reading distance is impossible even with the most suitable lenses. STRAIN ON THE ACCOMMODATION. When a near-sighted person is given a pair of concave lenses of sufficient strength to completely correct his defect, the eyes are thereby rendered emmetropic, and when reading- is attempted with these glasses the accommodation is called upon for the same amount of effort as in a normal eye. But as has already been stated the accommodation in myopic eyes is always feeble, the more so the higher the degree of defect, and hence it is not equal to the task; so that to ask such a person to read through concave glasses of full correction is to expect an impossibility; or else it is accomplished at the expense of a great strain upon the accommodation, which is lessened if the book be held at an inconveniently great dis- tance from the eyes. There is one thing about concave glasses of which patients frequently complain, and that is they make everything seem smaller. This is partly real and partly comparative. Concave lenses have the property of making objects smaller just as convex lenses magnify them. But besides this, to the uncor- rected myopic eye on account, of its increased refractive power MYOPIA. 189 objects appear larger tlian they really are and their outlines imperfect; concave lenses concentrate the sight, make the out- lines of objects distinct, and in contrast with tlic former vision, smaller. SURGICAL TREATMENT OF MYOPIA. This chapter would be incomplete without some reference to the surgical treatment of myopia, that is, the removal of the crystalline lens for the purpose of reducing the exces- sive refraction. It cannot be denied that in theory this method of treatment is most excellent, and forms an ideal way of neu- tralizing the defect. While it is sound in theory and feasible in practice, and attractive to the ophthalmic surgeon who is making a brilliant reputation by skillful operations, yet when it is considered entirely from the patient's standpoint it will scarcely become a popular procedure. Unlike a strabismus operation which does not open the cavity of the eye-ball, the removal of the crystalline lens is a most serious matter and violently disturbs the normal condi- tion of the organ of vision. The parts most affected are the ciliary region and adjoining portions, a region which is par- ticularly liable to inflammatory reaction after injury or opera- tion. This is shown in the history of cataract onerations, where an occasional eye will go wrong without any apparent cause and in spite of every precaution i:)cing taken to avoid such a calamity. A case of myopia and one of cataract have no points in common. The latter has practically lost his sight and there is only one means by which it can be restored, and hence while he has everything to gain by an operation, he has nothing to lose in case it is unsuccessful, as he is a blind man in either case. In myopia on the other hand, even in the highest de- grees of defect, a fair amount of vision is always obtain.able by means of properly adjusted glasses, which might be entirely lost by the failure of the operation. Besides, there is some risk that the operation might give rise to detachment of the retina, and the possibility of such a disastrous sequence might well make the boldest surgeon hesitate. Many hundreds of cases of removal of a normal crystal- line lens for the relief of high myopia have been reported in 11»0 MYOPIA. liiiropc. particularly in (lermanv. lUit so far this country has furnished very few such cases, and in view of the readiness of our surgeons to take up new operations, this certainly speaks well for their conservatism. Perhaps an additional reason may he found in the fact that we have given more attention to the correction of extreme myopia by lenses than is the case abroad. The writer neither commends nor condemns this operation. nor do we think our readers should ever assume the responsi- bility of advising for or against it, but such grave cases should rather be referred to the ophthalmic surgeon for advice and such treatment as he may deem necessar}\ At the same time we feel the optician should be kept advised of the latest knowl- edge on this subject and of the optical i)rinci])les involved. DEGREE OF MYOPIA CALLING FOR OPERATION. . The first thought that arises in the consideration of this subject is as to the amount of myopia that would suggest the advisability of removing the crystalline lens. Some operators would place the limit at lo D., others at 14 D., while still others would extend it to 16 D. Of course the higher the degree, the greater might be considered the need for the operation. It seems reasonable to place the lower limit at about 14 D., because the reduction in the amount of myopia by the extraction of the lens, while it varies in different eyes, will scarcely be less than 14 D. and may extend to 20 D. Therefore, in a case of 10 D. the removal of the crystalline lens would leave the patient markedly hypermetropic, so that there would scarcely be any advantage in its removal, unless possibly in the hope of preventing an increase in the defect, if the same seemed imminent. But it is an error to suppose that every case of myopia of 8 D. or 10 D. is progressive, or that there is danger of approacliing blindness. THE REFRACTION OF APIIAKIAL EYES. This leads to a consideration of the changes brought about in the refraction of an eye by the loss of its crystalline lens, concerning- which there has been much misunderstand- ing and many misstatements in the current literature of the MVOl'IA. 11>1 siil)ject. Iii the ordinary cases of aphakia after cataract oper- ation, the previousl\' emmetropic eye calls for a lens of about -f ID D., from which it mi^lil he inferred that the extraction of the crystalline lens in myopia would lessen the defect by about ID D. But a clear understanding- of the optical prin- ciples involved shows that it does more than this, which is also corroborated by experience. A + lo D. cataract lens, placed as it usually is about half- inch in front of the eye, would be equal to about i6 D. of re- fractive power of a crystalline lens in its i)lace. This fact is in accord with the princijiles of optics, and partly accounts for the wonderful refractive changes which aphakia produces in high degrees of myopia. But the arguments in favor of this operation rest not alone upon a neutralization of the myopia or a reduction in the strength of the concave lenses, but also upon the probabilitx of checking an increasing myopia and the retino-choroiditis tlial accompanies it. In this direction the operation promises much, not in the positive improvement of every eye any more than cNcry cataract operation can be guaranteed to be successful. Imt a satisfactory result in a fairly g-ood proportion of cases. ACK FOR OPERATION. When the operation is performed on cases between the ages of ten and twenty-five years the best results are attained. Under ten years of age it is rare to find myopia sufficiently high to justify an operation, while in those older than twenty- five the myopia has ceased to progress, or else the changes at the fundus are such as to contra-indicate an operation This latter is really an important factor; a very careful oph- thalmoscopic examination must be made lo determine tlv,- amount of retinal and choroidal change, on which will de- pend the benefit that can be expected and by which the sur- geon will be guided in arriving at a conclusion as to the ad- visability of the procedure. The limit of age has been placed as high as fifty years, but the fact is that patients past thirty years of age will rarely submit to an operation, because they have become accustomed to their condition and their vision does not grow any worse. 192 SHOULD BOTH KVES BE OPERATED OX f This is a question about which there is a good deal of difference of opinion. The truth is that if one eye -was fairly good the operation would be scarcely justifiable, and it would only be resorted to in case both eyes were equally bad, in which case it would seem as if the binocular operation was proper. DOXDERS' WORDS. In this connection it is interesting to read the words of Bonders, uttered forty years ago. He says, "When in a case of highly myopic structure of an eye, a lens affected with cataract has been successfully extracted and a nearly emme- tropic condition has been obtained, the operator has been exposed to the temptation of endeavoring, by the abstraction of a normal lens, to remove the myopia. A patient who was an amateur in dioptrics endeavored to induce me to perform this operation. "But I need not say that such a momentous undertaking, doubly dangerous where a myopic and a transparent lens are concerned, without that, even in the most favorable cases, any real advantage is to be expected, would exhibit culpable rashness. Not only would the staphyloma posticum continue equally threatening, but w'e should also have sacrificed the accommodation — an advantage which that of somewhat larger images than would be obtainable by neutralizing glasses, could by no means counterbalance." RESULTS OF THE OPERATION. The amount of vision to be obtained by an operation will depend upon the fundus changes, modified by the surgeon's skill in performing his work. Cases have been reported where it was impossible by any glasses to raise the vision to oW? or in other words to enable the patient to see even the largest letter on the test card at a distance of twenty feet, where a vision of f ^ was secured after the extraction of the crystalline lens. This is certainly a remarkable result, which cannot be accounted for by a simple reduction in the amount of myopia; but there are in rultiition three laetors that enter iiU(» tlie question : First, the size of the retinal image is inereased. This varies with the amount of ametropia remaining after the oper- ation, it being one and a half times larger when the aphakial condition is ennnetropic. Second, the retinal illumination is greater. In a highlv myopic eye the strong concave lens that is required diverges or scatters the rays of light, and hence fewer of them can enter the eye than in ennnetropic aphakia, where the rays would be nearly parallel. Third, the disiK-rsion of light is less. If a case of corrected myopia is compared with a case of emmetropic aphakia, it will be seen that there are at least five refracting surfaces in the former condition as against one in the latter, or against three in a case of aphakia that requires glasses; with the advantage in the latter case that the glasses required would be much weaker than the strong concave lenses used before the oper- ation, and therefore there is less rellection and less aberration. THE LOS.S OF ACCOMMODATION .\FTKR OlMlKATlOX. One of the points used agamst the advisability of the operation under consideration is that the increased acuteness of vision is nullified by the loss of accommodation, but a close consideration of this argument robs it of some of its strength. After the usual cataract extraction the glasses required for distance and reading may range from + lo D. to + 20 D. Such strong glasses focus the rays of light upon the retina at a very acute angle, and hence a slight displacement of the object quickly throws the retinal nnage out of focus. On the other hand, in the elongated eye of myopic aphakia the rays reach the retina at a greatly reduced angle, which admits of considerable variation in the position of the object viewed without throwing it much out of focus. Besides, even if lenses are recjuired in myopic aphakia, they arc of such low refractive power that they can be made up as bifocals, and if accurately prescribed and carefully adjusted, will prove of great convenience and secure for the patient the 194 MYOPIA. brightest degree of vision wliich surgical skill has rendered possible. op.\ciTii:s OF Till-: cornea. Opacities of the cornea, which have resulted from some preceding inflammation, may seriously impair the vision, and yet escape notice on a casual examination. Inasmuch as a clouded cornea lessens the visual acuteness and causes the patient to hold his book close to his eyes, thus simulating myopia, the optician who fits glasses for the correction of this defect should be on his guard, and must be able to exclude a defective cornea as a cause of the impaired vision. The transparency of the cornea is best determined by oblique illumination by a convex lens, as described and illustrated in the chapter on "Method of Examination." It would be rather embarrassing for the optician, after putting the patient through a tedious and fruitless examination w'ith the trial case, to learn that the so-called myopia w^as due to scars on the cornea, and hence could not be remedied by glasses. CAUTION IN PRESCRIBING CONCAVE LENSES FOR YOUNG PEOPLE. In the early part of the chapter reference w-as made to apparent or accommodative or false myopia, and the necessity for its recognition in order to avoid falling into the danger of giving concave glasses when myopia was not really present. Such a condition results from spasm of the accommodation, and is most apt to occur in youth; therefore, it is not always proper and safe to give concave glasses to all young persons indiscriminately, simply because their vision was improved by them. This is a truth that is universally recognized, as is evidenced by the following question taken from those given at the written examination for the diploma of the Worshipful Company of Spectacle Makers of England, November i, 1898. "Question No. 9. — ^A boy aged twelve has vision — |, but with a concave lens of 1.25 D. he has vision |. What tests would you employ to ascertain the nature of his defect?" The answer, as prepared by the examiners in charge, is: "It is very unlikely that this is true myopia. I should test for astigmatism in the usual way, and also for hyperopia, by taking the place of the near point, and by these means ascertain the MYOPIA. 195 real nature of the defect. It is almost certainly astigmatism, either myopic, or perhaps hyperopic." The serious condition of an eye afYected with high myopia and the responsibility involved in prescribing glasses in such cases is emphasized by the following question taken from the same examination: "Question No. ii. — A youth aged twelve sees best with — 14 D. Would you give him this correction on vour own responsibility? And if not, state your reasons." The answer prepared was: "On my own responsibility I would not give glasses in this case. I should look upon it as a diseased condition, and as one that is likely to increase seri- ously unless proper medical treatment be obtained." VALUE OF CON'CAVE GLASSES. Roosa says: "Gustavus Adolphus was near-sighted, and it is said that he lost his life at the battle of Lutzen because he had no correcting lenses and got among the soldiers of the enemy, thinking them to be his own." One of the most suc- cessful Union generals of the late war, more fortunate than the great Swedish commander, was wise enough to recognize the fact that he was astigmatic, and ordered a pair of cylindrical glasses to be ground for himself, with which he said he was enabled to be a much better soldier than without them. Yet a great many people — and by no means are they always unintelligent and uneducated — prefer to see as thev have always done, "in a beautiful haze," as one lady once described her short-sighted vision to me, than to be startled by seeing distant objects with distinctness. But there are myopic persons who appreciate the delight of seeing well. One of my New York patients, a full-grown woman, after her eyes had been fitted with a pair of concave cylindrics, with which she probably saw clearly at a distance for the first time in her life, told me that after passing down Broadway she turned and walked up, because, to use her graphic language, "I have had seen the street before, although I was bom very near it." "It has been said that the Jews have more myopia than other people. There seems to bo no valid ground for this as- IOC MYOPIA. sumption other than can 1)0 found in the fact that Jewish vocations the world over are usually those of shop-keepers, nioney-chang^ers. etc.. which necessitates close application to books and textures. In countries where the great mass of the inhabitants turn to open-air employments, and the Jew, naturally, gravitates toward commercial life, no surprise need be experienced if an examination of scholars shows a wide discrepancy in the development of myopia. Proof, however, fails to demonstrate the same variance where Jew and Christian are reared alike, and where inherited tendencies from one generation to another can be estimated upon a basis of similarity." A CASE OF HIGH MVOl'lA. Mrs. E. S^ . Aged thirty years. Complains that eyes ])ain her and she is compelled to hold everything so very close to her eyes in order to see. Has always been near-sighted, but never wore glasses. She is not able to see the test card across the room, much less any letters on it. — i8 D. lenses gave her the best vision, with which, how^ever, she could read only the No. 70 line, and there was nO' other glass that enabled her to read any lower. But although an emmetrope would consider this very poor sight, yet it is so very, very much better than she has been able to see at any time in her life, that she thinks the glasses are splendid. According to the rule given in this chapter, we would deduct about 3 D. for the read- ing glasses, but a trial shows that — 14 D. gives her the best vision for close work. Hence — 18 D. was ordered for general wear and distant vision and — 14 D. for close use. Six weeks later her husband reported glasses as very satisfactory and couldn't do without them. There are two conclusions that can be pretty ceitainly drawn from this case, and the first is that if she had com- menced to wear glasses in youth, as she should have done, a much weaker glass would have sufficed, and the defect would not have increased to such a serious degree. The second is that the failure of the present glasses to raise the visual acute- ness to normal is due to a partial amblyopia, or a blunted sensibility of the retina, which in turn was caused by the circles of diffusion which have been formed on this membrane for the MNOIMA. 1^>^ past thirty years. Rays of lig:lit did not focus ui>on the retina naturally, nor were they made to do so artificially, and hence a focal point was unknown upon this membrane and clear vision had never been experienced, and as a consefjuence its impressibility was markedly lessened. MVOIM.\ ]X KKLATIOX TO EVE-STRAI X. There is no power an eye possesses that will overcome myopia or improve the defect in vision except by compressing- the eye-ball slightly in squinting or half closing the lids; hence myopic persons are not subject to the muscular strain which hypemietropes constantly and unconsciously exert in order to be able to enjoy clear vision. As soon as the latter of>ens his lids the accommodation instinctively contracts, to prevent the diffusion circles that would otherwise be formed upon the retina; whereas in myopia these circles cannot be dissipated by any amount of muscular effort, a tension of the accommo- dation only serving to make them more pronounced. Besides, a myopic eye can read and perform all the functions required of it. when book or paper is held sufficiently close to the eyes, with less accommodative eflfort than in a normal eye. In contrast with which the hypermetropic eye is called upon to exert an unnatural effort of acconmiodation even for distant vision, which is much intensified when en- gaged in close work; hence the fatigue, the blurring of letters upon a printed page, the watering of eyes, the pain in head and eyes, and the many other ills that have been described in the previous chapter. Myopes can scarcely help being aware of some defect in their- vision, because of their inability to see across the room distinctly or to recognize friends on the street. Thus they naturally gravitate to occupations where the work is brought close to the eyes, because they have no difficulty in seeing near objects. Near-sighted children are liable to be considered precocious beyond their years, because they prefer to read rather than to play out-of-doors. It is generally safe to con- clude that a child is near-sighted when it avoids the usual 198 MYOPIA. g^ames of childlioocl in order to £::ratifv a taste for reading and in-door amusements. Myopia is less liable to cause nervous disturbances, ex- cept it leads to muscular insufHciency and asthenopia. And yet the number of myopes applying for relief is not small, be- cause the defect of vision is so apparent and cannot be con- cealed by an effort of the eye, as in hypermetropia. The writer can speak of myopia from a personal stand- point. When a student in the medical department of the Uni- versity of Pennsylvania, his eyes were examined under atro- pine by Dr. Risley at the commencement of the course, twenty- four years ago, and were found slightly hypermetropic and weak convex glasses prescribed. The excessive demands upon the eyes in pursuing the prescribed studies resulted in asthenopia and a continued trouble with eyes all through the course, until at graduation in 1878 a myopia of 2 D. was found to be present, and Dr. Risley considered the case of sufficient interest and importance to make and publish a report of it, as illustrating the production of myopia. At that time this sub- ject was being generally discussed, and examinations of school children were being made on large scale in this country and abroad in order to determine the exact relation between school life and study, and the causation of near-sightedness; and the Avriter's case formed an apt illustration, and was one among many which proved the dire effects of excessive application in causing an elongation of eye-ball. APPENDIX. Optical Symbols and Abbreviations. ^f. Accommodation. Aet Age. j^jY\ Ametropia. An Anisometropia. /^s 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. HI Latent Hypermetropia. Hm Manifest Hypermetropia. Ht Total Hypermetropia. In. ... Inches. L. or L. E Left Eye. M. or My Myopia. Mm Millimeter. N Nasal. Nv Naked Vision. O. D. (Oculus Dexter) Right Eye. O. S. (Oculus Sinister) Left Eye. O. U. (Oculi Unati) Both Eyes. P. or Pb Presbyopia. 199 200 APPI-NDIX. P. Cc Periscopic Concave. P. Cx Periscopic Convex. P. D Inter-Pupillary Distance. PI Piano. p. p. (Punctum Proximum) Near Point, p. r. (Punctum Reniotum) . 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 3 .... , Combined with. L At Right Angles. ° Degree. A Prism-Diopter. ' Foot and Minute. " Inch and Second. "' Line, the twelfth part of an inch. = Equal to. CO Infinitv. 20 feet or further. The Shadow Test and Use of the Retinoscope THIS NEW WORK ON SKIASCOPY far excels all previous treat- ises on the subject in compn:-hensivene>- and practical value to the refractionist. It not only explains the shadow test in its practical application to the work of refraction, but expounds fully and explicitly the optical principles underlying it. In depth of research, wealth of illustration and scientific completeness this work is unic[ue. Bound in cloth ; contains 231 pages— 73 illustrations and colored plates. Sent postpaid on receipt of $l.50. Published by The Keystone, 19TH & Brown Sts., Phii adklihi a, Pa., U.S.A. 201 NOTICE TO READERS. The Optician s Manual is a republication in book form of the serial The Optician's Manual published monthly in The Keystone, from May, 1890, to November, 1896, inclusive. While the serial, as published with much new matter and illustrations in this second edition, covers the science of practical optics, it is the intention to continue the serial in The Keystone in order to make it, when complete, not only the standard treatise on optical science as a whole, but the most complete and comprehensive work on each subdivision of the science. It will be necessary, therefore, for optical readers who desire to study Hypermetropia, Myopia, Astigmatism, Asthenopia and Muscle Test at greater length and in minutest detail, to continue to read The Optician's Manual in The Keystone, as several years will elapse before the continuation of the serial will be complete and procurable in book form. For this and other reasons a perusal each month of the Optical Department of The Keystone will make the present work doubly valuable. Address. THE KEYSTONE The Organ of the Jewelry and Optical Trades 19th & Brown Sts., Philadelphia, Pa., U. 5. A. Suhsctiption Price, for the United States, Canada and Mexico, ONE DOLLAR PER ANSUM. For Foreign Countries, $2.44 (los.) 202 OPTOMETRIC RECORD-BOOK. A record-book, wherein to record optometric examina- tions, is an indispensable adjunct of an optician's outfit. The Keystone Optometric Record-book was specially prepared for this purpose. It excels all others in being not only a record-book, but an invaluable guide in examination. The book contains two hundred record forms with printed headings, suggesting, in the proper order, the course of ex- amination that should be pursued to obtain most accurate results. Each book has an index, which enables the optician to refer instantly to the case of any particular patient. The Keystone Record-book diminishes the time and labor required for examinations, obviates possible oversights from carelessness, and assures a systematic and thorough ex- amination of the eye, as well as furnishes a permanent record of all examinations. Sent Postpaid on Receipt of $1.00. Published by THE KEYSTONE, The Organ of the Jewelry and Optical Trades Nineteenth and Brown Sis., Philadelphia, Pa., U. S. A. 203 RETURN OPTOMETRY LIBRARY TO— ^ 215 Minor Hall 642-1020 LOAN PERIOD 1 2 3 4 5 6 ALL BOOKS MAY BE RECALLED AFTER 7 DAYS DUE AS STAMPED BE LOW UNIVERSITY OF CALIFORNIA, BERKELEY FORAANO.DD23, 2.5m, 477 BERKELEY, CA 94720 ^^ ,.if„9 ?i?HLEY LMARIES