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By W. H. BATES, M.D.
TO THE MEMORY OF THE PIONEERS OF OPHTHALMOLOGY THIS BOOK IS GRATEFULLY DEDICATED
On a tomb in the Church of Santa Maria Maggiore in Florence was found an inscription which read: "Here lies Salvino degli Armati, Inventor of Spectacles. May God pardon him his sins."
Nuova Enciclopedia Italiana, Sixth Edition.
Do you read imperfectly? Can you observe then that when you look at the first word, or the first letter, of a sentence you do not see best where you are looking; that you see other words, or other letters, just as well as or better than the one you are looking at? Do you observe also that the harder you try to see the worse you see? Now close your eyes and rest them, remembering some color, like black or white, that you can remember perfectly. Keep them closed until they feel rested, or until the feeling of strain has been completely relieved. Now open them and look at the first word or letter of a sentence for a fraction of a second. If you have been able to relax, partially or completely, you will have a flash of improved or clear vision, and the area seen best will be smaller.
After opening the eyes for this fraction of a second, close them again quickly, still remembering the color, and keep them closed until they again feel rested.
Then again open them for a fraction of a second. Continue this alternate resting of the eyes and flashing of the letters for a time, and you may soon find that you can keep your eyes open longer than a fraction of a second without losing the improved vision.
If your trouble is with distant instead of near vision, use the same method with distant letters.
In this way you can demonstrate for yourself the fundamental principle of the cure of imperfect sight by treatment without glasses.
If you fail, ask someone with perfect sight to help you.
FERDINAND VON ARLT (1812-1887) Distinguished Austrian ophthalmologist, Professor of Diseases of the Eye at Vienna who believed for a time that accommodation was produced by an elongation of the visual axis, but finally. accepted the conclusions of Cramer and Helmholtz.
This book aims to be a collection of facts and not of theories, and insofar as it is, I do not fear successful contradiction. When explanations have been offered it has been done with considerable trepidation, because I have never been able to formulate a theory that would withstand the test of the facts either in my possession at the time, or accumulated later. The same is true of the theories of every other man, for a theory is only a guess, and you cannot guess or imagine the truth. No one has ever satisfactorily answered the question, "Why ?" as most scientific men are well aware, and I did not feel that I could do better than others who had tried and failed. One cannot even draw conclusions safely from facts, because a conclusion is very much like a theory, and may be disproved or modified by facts accumulated later. In the science of ophthalmology, theories, often stated as facts, have served to obscure the truth and throttle investigation for more than a hundred years. The explanations of the phenomena of sight put forward by Young, von Graefe, Helmholtz and Donders have caused us to ignore or explain away a multitude of facts which otherwise would have led to the discovery of the truth about errors of refraction and the consequent prevention of an incalculable amount of human misery.
In presenting my experimental work to the public, I desire to acknowledge my indebtedness to Mrs. E. C. Lierman, whose co-operation during four years of arduous labor and prolonged failure made it possible to carry the work to a successful issue. I would be glad, further, to acknowledge my debt to others who aided me with suggestions, or more direct assistance, but am unable to do so, as they have requested me not to mention their names in this connection.
As there has been a considerable demand for the book from the laity, an effort has been made to present the subject in such a way as to be intelligible to persons unfamiliar with ophthalmology.
MOST writers on ophthalmology appear to believe that the last word about problems of refraction has been spoken, and from their viewpoint the last word is a very depressing one. Practically everyone in these days suffers from some form of refractive error. Yet we are told that for these ills, which are not only so inconvenient, but often so distressing and dangerous, there is not only no cure, and no palliatives save those optic crutches known as eyeglasses, but, under modern conditions of life, practically no prevention.
It is a well known fact that the human body is not a perfect mechanism. Nature, in the evolution of the human tenement, has been guilty of some maladjustments.
She has left, for instance, some troublesome bits of scaffolding, like the vermiform appendix, behind. But nowhere is she supposed to have blundered so badly as in the construction of the eye. With one accord ophthalmologists tell us that the visual organ of man was never intended for the uses to which it is now put. Eons before there were any schools or printing presses, electric lights or moving pictures, its evolution was complete. In those days it served the needs of the human animal perfectly. Man was a hunter, a herdsman, a farmer, a fighter.
He needed, we are told, mainly distant vision; and since the eye at rest is adjusted for distant vision, sight is supposed to have been ordinarily as passive as the perception of sound, requiring no muscular action whatever.
Fig. 1. Patagonians The sight of this primitive pair and of the following groups of primitive people was tested at the World's Fair in St. Louis and found to be normal. The unaccustomed experience of having their pictures taken, however, has evidently so disturbed them that they were all, probably, myopic when they faced the camera. (see Chapter IX.)
Near vision, it is assumed, was the exception, necessitating a muscular adjustment of such short duration that it was accomplished without placing any appreciable burden upon the mechanism of accommodation. The fact that primitive woman was a seamstress, an embroiderer, a weaver, an artist in all sorts of fine and beautiful work, appears to have been generally forgotten. Yet women living under primitive conditions have just as good eyesight as the men.
Fig. 2. African Pigmies They had normal vision when tested, but their expressions show that they could not have had it when photographed.
When man learned how to communicate his thoughts to others b means of written and printed forms, there came some undeniably new demands upon the eye, affecting at first only a few people, but gradually including more and more, until now, in the more advanced countries, the great mass of the population is subjected to their influence. A few hundred years ago even princes were not taught to read and write. Now we compel everyone to go to school, whether he wishes to or not, even the babies being sent to kindergarten. A generation or so ago books were scarce and expensive. To-day, by means of libraries of all sorts, stationary and traveling, they have been brought within the reach of practically everyone. The modern newspaper, with its endless columns of badly printed reading matter, was made possible only by the discovery of the art of manufacturing paper from wood, which is a-thing of yesterday. The tallow candle has been but lately displaced by the various forms of artificial lighting, which tempt most of us to prolong our vocations and avocations into hours when primitive man was forced to rest, and within the last couple of decades has come the moving picture to complete the supposedly destructive process.
Was it reasonable to expect that Nature should have provided for all these developments, and produced an organ that could respond to the new demands? It is the accepted belief of ophthalmology to-day that she could not and did not,1 and that, while the processes of civilization depend upon the sense of sight more than upon any other, the visual organ is but imperfectly fitted for its tasks.
There are a great number of facts which seem to justify this conclusion. While primitive man appears to have suffered little from defects of vision, it is safe to say that of persons over twenty-one living under civilized conditions nine out of every ten have imperfect sight, and as the age increases the proportion increases, until at forty it is almost impossible to find a person free from visual defects. Voluminous statistics are available to prove these assertions, but the visual standards of the modern army2 are all the evidence that is required.
In Germany, Austria, France and Italy the- vision with glasses determines acceptance or rejection for military service, and in all these countries more than six diopters3 of myopia are allowed, although a person so handicapped cannot, without glasses, see anything clearly at more than six inches from his eyes. In the German Army a recruit for general service is required—or was required under the former government—to have a corrected vision of 6/12 in one eye. That is, he must be able to read with this eye at six metres the line normally read at twelve metres. In other words, he is considered fit for military service if the vision of one eye can be brought up to one-half normal with glasses. The vision in the other eye may be minimal, end in the Landsturm one eye may be blind. Incongruous as the eyeglass seems upon the soldier, military authorities upon the European continent have come to the conclusion that a man with 6/12 vision wearing glasses is more serviceable than a man with 6/24 vision (one-quarter normal) without them.
In Great Britain it was formerly uncorrected vision that determined acceptance or rejection for military service. This was probably due to the fact that previous to the recent war the British Army was used chiefly for foreign service, at such distances from its base that there might have been difficulty in providing glasses.
Fig. 3. Moros from the Philippines With sight ordinarily normal all were probably myopic when photographed except the one at the upper left whose eyes are shut.
The standard at the beginning of the war was 6/24 (uncorrected) for the better eye and 6/60 (uncorrected) for the poorer, which was required to be the left. Later, owing to the difficulty of securing enough men with even this moderate degree of visual acuity, recruits were accepted whose vision in the right eye could be brought up to 6/12 by correction, provided the vision of one eye was 6/24 without correction.4
Up to 1908 the United States required normal vision in recruits for its military service. In that year Bannister and Shaw made some experiments from which they concluded that a perfectly sharp image of the target was not necessary for good shooting, and that, therefore, a visual acuity of 20/40 (the equivalent in feet of 6/12 in metres), or even 20/70, in the aiming eye only, was sufficient to make an efficient soldier. This conclusion was not accepted without protest, but normal vision had become so rare that it probably seemed to those in authority that there was no use insisting upon it; and the visual standard for admission to the Army was accordingly lowered to 20/40 for the better eye and 20/100 for the poorer, while it was further provided that a recruit might be accepted when unable with the better eye to read all the letters on the 20/40 line, provided he could read some of the letters on the 20/30 line.5 In the first enrollment of troops for the European war it is a matter of common knowledge that these very low standards were found to be too high and were interpreted with great liberality. Later they were lowered so that men might be "unconditionally accepted for general military service" with a vision of 20/100 in each eye without glasses, provided that the sight of one eye could be brought up to 20/40 with glasses, while for limited service 20/200 in each eye was sufficient, provided the vision of one eye might be brought up to 20/40 with glasses.6 Yet 21.68 per cent of all rejections in the first draft, 13 per cent more than for any other single cause, were for eye defects,7 while under the revised standards these defects still constituted one of three leading causes of rejection. They were responsible for 10.65 per cent of the rejections, while defects of the bones and joints and of the heart and bloodvessels ran, respectively, about two and two and a half per cent higher.8 For more than a hundred years the medical profession has been seeking for some method of checking the ravages of civilization upon the human eye. The Germans, to whom the matter was one of vital military importance, have spent millions of dollars in carrying out the suggestions of experts, but without avail; and it is now admitted by most students of the subject that the methods which were once confidently advocated as reliable safeguards for the eyesight of our children - have accomplished little or nothing. Some take a more cheerful view of the matter, but their conclusions are hardly borne out by the army standards just quoted.
For the prevailing method of treatment, by means of compensating lenses, very little was ever claimed except that these contrivances neutralized the effects of the various conditions for which they were prescribed, as a crutch enables a lame man to walk. It has also been believed that they sometimes checked the progress of these conditions; but every ophthalmologist now knows that their usefulness for this purpose, if any, is very limited. In the case of myopia9 (shortsight), Dr. Sidler-Huguenin of Zurich, in a striking paper recently published,10 expresses the opinion that glasses and all methods now at our command are "of but little avail" in preventing either the progress of the error of refraction, or the development of the very serious complications with which it is often associated.
These conclusions are based on the study of thousands of cases in Dr. Huguenin's private practice and in the clinic of the University of Zurich, and regarding one group of patients, persons connected with the local educational institutions, he states that the failure took place in spite of the fact that they followed his instructions for years "with the greatest energy and pertinacity," sometimes even changing their professions.
I have been studying the refraction of the human eye for more than thirty years, and my observations fully confirm the foregoing conclusions as to the uselessness of all the methods heretofore employed for the prevention and treatment of errors of refraction. I was very early led to suspect, however, that the problem was by no means an unsolvable one Every ophthalmologist of any experience knows that the theory of the incurability of errors of refraction does not fit the observed facts. Not infrequently such cases recover spontaneously, or change from one form to another. It has long been the custom either to ignore these troublesome facts, or to explain them away, and fortunately for those who consider it necessary to bolster up the old theories at all costs, the role attributed to the lens in accommodation offers, in the majority of cases, a plausible method of explanation. According to this theory, which most of us learned at school, the eye changes its focus for vision at different distances by altering the curvature of the lens; and in seeking for an explanation for the inconstancy of the theoretically constant error of refraction the theorists hit upon the very ingenious idea of attributing to the lens a capacity for changing its curvature, not only for the purpose of normal accommodation, but to cover up or to produce accommodative errors. In hypermetropia11—commonly but improperly called farsight, although the patient with such a defect can see clearly neither at the distance nor the nearpoint—the eyeball is too short from the front backward, and all rays of light, both the convergent ones coming from near objects, and the parallel ones coming from distant objects, are focussed behind the retina, instead of upon it. In myopia it is too long, and while the divergent rays from near objects come to a point upon the retina, the parallel ones from distant objects do not reach it. Both these conditions are supposed to be permanent, the one congenital, the other acquired. When, therefore, persons who at one time appear to have hypermetropia, or myopia, appear at other times not to have them, or to have them in lesser degrees, it is not permissible to suppose that there has been a change in the shape of the eyeball. Therefore, in the case of the disappearance or lessening of hypermetropia, we are asked to believe that the eye, in the act of vision, both at the near-point and at the distance, increases the curvature of the lens sufficiently to compensate, in whole or in part, for the flatness of the eyeball. In myopia, on the contrary, we are told that the eye actually goes out of its way to produce the condition, or to make an existing condition worse.
Fig. 4. Diagram of the Hypermetropic, Emmetropic and Myopic Eyeballs H, hypermetropia; E, emmetropia; M, myopia; Ax, optic axis. Note that in hypermetropia and myopia the rays, instead of coming to a focus, form a round spot upon the retina.
In other words, the so-called "ciliary muscle," believed to control the shape of the lens, is credited with a capacity for getting into a more or less continuous state of contraction, thus keeping the lens continuously in a state of convexity which, according to the theory, it ought to assume only for vision at the nearpoint. These curious performances may seem unnatural to the lay mind; but ophthalmologists believe the tendency to indulge in them to be so ingrained in the constitution of the organ of vision that, in the fitting of glasses, it is customary to instill atropine—the "drops" with which everyone who has ever visited an oculist is familiar—into the eye, for the purpose of paralyzing the ciliary muscle and thus, by preventing any change of curvature in the lens, bringing out "latent hypermetropia" and getting rid of "apparent myopia." The interference of the lens, however, is believed to account for only moderate degrees of variation in errors of refraction, and that only during the earlier years of life. For the higher ones, or those that occur after fortyfive years of age, when the lens is supposed to have lost its elasticity to a greater or less degree, no plausible explanation has ever been devised. The disappearance of astigmatism,12 or changes in its character, present an even more baffling problem.
Due in most cases to an unsymmetrical change in the curvature of the cornea, and resulting in failure to bring the light rays to a focus at any point, the eye is supposed to possess only a limited power of overcoming this condition; and yet astigmatism comes and goes with as much facility as do other errors of refraction. It is well known, too, that it can be produced voluntarily. Some persons can produce as much as three diopters. I myself can produce one and a half.
Examining 30,000 pairs of eyes a year at the New York Eye and Ear Infirmary and other institutions, I observed many cases in which errors of refraction either recovered spontaneously, or changed their form, and I was unable either to ignore them, or to satisfy myself with the orthodox explanations, even where such explanations were available. It seemed to me that if a statement is a truth it must always be a truth. There can be no exceptions. If errors of refraction are incurable, they should not recover, or change their form, spontaneously.
Fig. 5. The Eye As a Camera The photographic apparatus: D, diaphragm made of circular overlapping plates of metal by means of which the opening through which the rays of light enter the chamber can be enlarged or contracted- L, lens; R, sensitive plate (the retina of the eye); AB, object to be photographed; ab, image on the sensitive plate. The eye: C, cornea where the rays of light undergo a first refraction; D, iris (the diaphragm of the camera); L, lens, where the light rays are again refracted; R, retina of the normal eye; AB, object of vision; ab, image in the normal or emmetropic eye- at b', image in the hypermetropic eye; a" b", image in the myopic eye. Note that in a' b' and a" b" the rays are spread out upon the retina instead of being brought to a focus as in ab, the result being the formation of a blurred image.
In the course of time I discovered that myopia and hypermetropia, like astigmatism, could be produced at will; that myopia was not, as we have so long believed, associated with the use of the eyes at the near-point, but with a strain to see distant objects, strain at the near-point being associated with hypermetropia; that no error of refraction was ever a constant condition; and that the lower degrees of refractive error were curable, while higher degrees could be improved.
In seeking for light upon these problems I examined tens of thousands of eyes, and the more facts I accumulated the more difficult it became to reconcile them with the accepted views. Finally, about half a dozen years ago, I undertook a series of observations upon the eyes of human beings and the lower animals the results of which convinced both myself and others that the lens is not a factor in accommodation, and that the adjustment necessary for vision at different distances is affected in the eye, precisely as it is in the camera, by a change in the length of the organ, this alteration being brought about by the action of the muscles on the out side of the globe. Equally convincing was the demonstration that errors of refraction, including presbyopia, are due, not to an organic change in the shape of the eyeball, or in the constitution of the lens, but to a functional and therefore curable derangement in the action of the extrinsic muscles.
Fig. 6. Mexican Indians With normal sight when tested all the members of this primitive group are now either squinting or staring.
In making these statements I am well aware that I am controverting the practically undisputed teaching of ophthalmological science for the better part of a century; but I have been driven to the conclusions which they embody by the facts, and that so slowly that I am now surprised at my own blindness. At the time I was improving high degrees of myopia; but I wanted to be conservative, and I differentiated between functional myopia, which I was able to cure, or improve, and organic myopia, which, in deference to the orthodox tradition, I accepted as incurable.
Fig. 7. Ainus, the Aboriginal Inhabitants of Japan All show signs of temporary imperfect sight.
1. The unnatural strain of accommodating the eyes to close work (for which they were not intended) leads to myopia in a large proportion of growing children—Rosenau Preventive Medicine and Hygiene, third edition, 1917, p. 1093. The compulsion of fate as well as an error of evolution has brought it about that the unaided eye must persistently struggle against the astonishing difficulties and errors inevitable in its structure function and circumstance— Gould The Cause, Nature and Consequences of Eyestrain, Pop Sci Monthly, Dec., 1905. With the invention of writing and then with the invention of the printing-press a new element was introduced, and one evidently not provided for by the process of evolution The human eye which had been evolved for distant vision is being forced to perform a new part, one for which it had not been evolved, and for which it is poorly adapted The difficulty is being daily augmented—Scott The Sacrifice of the Eyes of School Children, Pop Sci Monthly, Oct., 1907.
2. Ford Details of Military Medical Administration published with the approval of the Surgeon General, U.S. Army, second revised edition, 1918, pp. 498-499.
3. A diopter is the focussing power necessary to bring parallel rays to a focus at one metre.
4. Tr. Ophth. Soc. U. Kingdom, vol. xxxviii, 1918, pp. 130-131.
5. Harvard Manual of Military Hygiene for the Military Services of the United States, published under the authority and with the approval of the Surgeon General, U. S. Army third revised edition, 1917, p. 195.
6. Standards of Physical Examination for the Use of Local Boards, District Boards, and Medical Advisory Boards under the Selective Service Regulations, issued through the office of the Provost Marshal General, 1918.
7. Report of the Provost Marshal General to the Secretary of War on the First Draft under the Selective Service Act, 1917.
8. Second Report of the Provost Marshal General to the Secretary of War on the Operations of the Selective Service System to December 20, 1918.
9. From the Greek myein, to close, and ops, the eye, literally a condition in which the subject closes the eye, or blinks.
10. Archiv f Augenh, vol. lxxix, 1915, translated in Arch. Ophth., vol. xlv, No. 6, Nov., 1916.
11. From the Greek hyper, over, rnetrors, measure, and ops, the eye.
12. From the Greek a, without, and stigma, a point
MUCH of my information about the eyes has been obtained by means of simultaneous retinoscopy. The retinoscope is an instrument used to measure the refraction of the eye. It throws a beam of light into the pupil by reflection from a mirror,; the light being either outside the instrument—above and behind the subject—or arranged within it by means of an electric battery. On looking through the sight-hole one sees a larger or smaller part of the pupil filled with light, which in normal human eyes is a reddish yellow, because this is the color of the retina, but which is green in a cat's eye, and might be white if the retina were diseased.
Fig. 8. The Usual Method of Using the Retinoscope The observer is so near the subject that the latter is made nervous, and this changes the refraction.
Unless the eye is exactly focussed at the point from which it is being observed, one sees also a dark shadow at the edge of the pupil, and it is the behavior of this shadow when the mirror is moved in various directions which reveals the refractive condition of the eye. If the instrument is used at a distance of six feet or more, and the shadow moves in a direction opposite to the movement of the mirror, the eye is myopic. If it moves in the same direction as the mirror, the eye is either hypermetropic or normal; but in the case of hypermetropia the movement is more pronounced than in that of normality, and an expert can usually tell the difference between the two states merely by the nature of the movement. In astigmatism the movement is different in different meridians. To determine the degree of the error, or to distinguish accurately between hypermetropia and normality, or between the different kinds of astigmatism, it is usually necessary to place a glass before the eye of the subject. If the mirror isconcave instead of plane, the movements described will be reversed; but the plane mirror is the one most commonly used.
This exceedingly useful instrument has possibilities which have not been generally realized by the medical profession. Most ophthalmologists depend upon the Snellen1 test card, supplemented by trial lenses, to determine whether the vision is normal or not, and to determine the degree of any abnormality that may exist. This is a slow, awkward and unreliable method of testing the vision, and absolutely unavailable for the study of the refraction of the lower animals, of infants, and of adult human beings under the conditions of life.
The test card and trial lenses can be used only under certain favorable conditions, but the retinoscope can be used anywhere. It is a little easier to use it in a; dim light than in a bright one, but it may be used in any light, even with the strong light of the sun shining directly into the eye. It may also be used under many other unfavorable conditions.
It takes a considerable time, varying from minutes to hours, to measure the refraction with the Snellen test card and trial lenses. With the retinoscope, however, it can be determined in a fraction of a second. By the former method it would be impossible, for instance, to get any information about the refraction of a baseball player at the moment he swings for the ball, at the moment he strikes it, and at the moment after he strikes it. But with the retinoscope it is quite easy to determine whether his vision is normal, or whether he is myopic, hypermetropic, or astigmatic, when he does these things; and if any errors of refraction are noted, one can guess their degree pretty accurately by the rapidity of the movement of the shadow.
With the Snellen test card and trial lenses conclusions must be drawn from the patient's statements as to what he sees; but the patient often becomes so worried and confused during the examination that he does not know what he sees, or whether different glasses make his sight better or worse; and, moreover, visual acuity is not reliable evidence of the state of the refraction. One patient with two diopters of myopia may see twice as much as another with the same error of refraction. The evidence of the test card is, in fact, entirely subjective; that of the retinoscope is entirely objective, depending in no way upon the statements of the patient.
In short, while the testing of the refraction by means of the Snellen test card and trial lenses requires considerable time, and can be done only under certain artificial conditions, with results that are not always reliable, the retinoscope can be used under all sorts of normal and abnormal conditions on the eyes both of human beings and the lower animals; and the results, when it is used properly, can always be depended upon. This means that it must not be brought nearer to the eye than six feet; otherwise the subject will be made nervous, the refraction, for reasons which will be explained later, will be changed, and no reliable observations will be possible. In the case of animals it is often necessary to use it at a much greater distance.
For thirty years I have been using the retinoscope to study the refraction of the eye. With it I have examined the eyes of tens of thousands of school children, hundreds of infants and thousands of animals, including cats, dogs, rabbits, horses, cows, birds, turtles, reptiles and fish. I have used it when the subjects were at rest and when they were in motion—also when I myself was in motion; when they were asleep and when they were awake or even under ether and chloroform. I have used it in the daytime and at night, when the subjects were comfortable and when they were excited; when they were trying to see and when they were not; when they were lying and when they were telling the truth; when the eyelids were partly closed, shutting off part of the area of the pupil, when the pupil was dilated, and also when it was contracted to a pin-point; when the eye was oscillating from side to side, from above downward and in other directions. In this way I discovered many facts which had not previously been known, and which I was quite unable to reconcile with the orthodox teachings on the subject.
This led me to undertake the series of experiments already alluded to. The results were in entire harmony with my previous observations, and left me no choice but to reject the entire body of orthodox teaching about accommodation and errors of refraction. But before describing these experiments I must crave the readers patience while I present a resume of the evidence upon which the accepted views of accommodation are based. This evidence, it seems to me, is as strong an argument as any I could offer against the doctrine that the lens is the agent of accommodation, while an understanding of the subject is necessary to an understanding of my experiments.
1. Herman Snellen (1835-1908). Celebrated Dutch ophthalmologist, professor of ophthalmology in the University of Utrecht and director of the Netherlandic Eye Hospital. The present standards of visual acuity were proposed by him, and his test types became the model for those now in use.
THE power of the eye to change its focus for vision at different distances has puzzled the scientific mind ever since Kepler1 tried to explain it by supposing a change in the position of the crystalline lens. Later on every imaginable hypothesis was advanced to account for it. The idea of Kepler had many supporters. So also had the idea that the change of focus was effected by a lengthening of the eyeball. Some believed that the contractive power of the pupil was sufficient to account for the phenomenon, until the fact was established, by the operation for the removal of the iris, that the eye accommodated perfectly without this part of the visual mechanism. Some, dissatisfied with all these theories, discarded them all, and boldly asserted that no change of focus took place,2 a view which was conclusively disproven when the invention of the ophthalmoscope made it possible to see the interior of the eye.
The idea that the change of focus might be brought about by a change in the form of the lens appears to have been first advanced, according to Landolt,3 by the Jesuit, Scheiner (1619). Later it was put forward by Descartes (1637). But the first definite evidence in support of the theory was presented by Dr. Thomas Young in a paper read before the Royal Society in 1800.4 "He adduced reasons," says Donders, "which, properly under stood, should be taken as positive proofs."5 At the time, however, they attracted little attention.
Fig. 9. Diagrams of the Images of Purkinje No. 1.—Images of a candle: a, on the cornea; b, on the front of the lens- c, on the back of the lens. No. 2.—Images of lights shining through rectangular openings in a screen while the eye is at rest (R) and during accommodation (A): a, on the cornea; b, on the front of the lens; c, on the back of the lens (after Helmholtz). Note that in No. 2, A, the central images are smaller and have approached each other, a change which, if it actually took place would indicate an increase of curvature in the front of the lens during accommodation.
About half a century later it occurred to Maximilian Langenbeck6 to seek light on the problem by the aid of what are known as the images of Purkinje.7 If a small bright light, usually a candle, is held in front of and a little to one side of the eye, three images are seen: one bright and upright; another large, but less bright, and also upright; and a third small, bright and inverted. The first comes from the cornea, the transparent covering of the iris and pupil, and the other two from the lens, the upright one from the front and the inverted one from the back. The corneal reflection was known to the ancients, although its origin was not discovered till later; but the two reflections from the lens were first observed in 1823 by Purkinje; whence the trio of images is now associated with his name.
Langenbeck examined these images with the naked eye, and reached the conclusion that during accommodation the middle one became smaller than when the eye was at rest. And since an image reflected from a convex surface is diminished in proportion to the convexity of that surface, he concluded that the front of the lens became more convex when the eye adjusted itself for near vision. Donders repeated the experiments of Langenbeck, but was unable to make any satisfactory observations. He predicted, however, that if the images were examined with a magnifier they would "show with certainty" whether the form of the lens changed during accommodation. Cramer,8 acting on this suggestion, examined the images as magnified from ten to twenty times, and thus convinced himself that the one reflected from the front of the lens became considerably smaller during accommodation.
Subsequently Helmholtz, working independently, made a similar observation, but by a somewhat different method. Like Donders, he found the image obtained by the ordinary methods on the front of the lens very unsatisfactory, and in his "Handbook of Physiological Optics" he describes it as being "usually so blurred that the form of the flame cannot be definitely distinguished.''9 So he placed two lights, or one doubled by reflection from a mirror, behind a screen in which were two small rectangular openings, the whole being so arranged that the lights shining through the openings of the screen formed two: images on each of the reflecting surfaces. During accommodations, it seemed to him that the two images on the front of the lens became smaller and approached each other, while on the return of the eye to a state of rest they grew larger again and separated This change, he said, could be seen "easily and distinctly."10 The observations of Helmholtz regarding the behavior of the lens in accommodation, published about the middle of the last century, were soon accepted as facts, and have ever since been stated as such in every text-book dealing with the subject.
"We may say," writes Landolt, "that the discovery of the part played by the crystalline lens in the act of accommodation is one of the finest achievements of medical physiology, and the theory of its working is certainly one of the most firmly established; for not only have "savans" furnished lucid and mathematical proofs of its correctness, but all other theories which have been advanced as explaining accommodation have been easily and entirely overthrown.... The fact that the eye is accommodated for near vision by an increase in the curvature of its crystalline lens, is, then, incontestably proved."11
Fig. 10. Diagram by Which Helmholtz Illustrated His Theory of Accommodation R is supposed t be the resting state of the lens, in which it is adjusted for distant vision. In A the suspensory ligament is supposed to have been relaxed through the contraction of the ciliary muscle, permitting the lens to bulge forward by virtue of its own elasticity.
"The question was decided," says Tscherning, "by the observation of the changes of the images of Purkinje during accommodation, which prove that accommodation is effected by an increase of curvature of the anterior surface of the crystalline lens."12
Fig. 11. Thomas Young (1773-1829) English physician and man of science who was the first to present a serious argument in support of the view that accommodation is brought about by the agency of the lens.
"The greatest thinkers," says Cohn, "have mastered a host of difficulties in discovering this arrangement, and it is only in very recent times that its processes have been clearly and perfectly set forth in the works of Sanson, Helmholtz, Brucke, Hensen and Volckers."13 Huxley refers to the observations of Helmholtz as the "facts of adjustment with which all explanations of that process must accord,"14 and Donders calls his theory the "true principle of accommodation."15 Arlt, who had advanced the elongation theory and believed that no other was possible, at first opposed the conclusions of Cramer and Helmholtz,16 but later accepted them.17 Yet in examining the evidence for the theory we can only wonder at the scientific credulity which could base such an important department of medical practice as the treatment of the eye upon such a mass of contradictions.
Helmholtz, while apparently convinced of the correctness of his observations indicating a change of form in the lens during accommodation, felt himself unable to speak with certainty of the means by which the supposed change was effected,18 and strangely enough the question is still being debated. Finding, as he states, "absolutely nothing but the ciliary muscle to which accommodation could be attributed,"19 Helmholtz concluded that the changes which he thought he had observed in the curvature of the lens must be effected by the action of this muscle; but he was unable to offer any satisfactory theory of the way it operated to produce these results, and he explicitly stated that the one he suggested possessed only the character of probability Some of his disciples, "more loyal than the king," as Tscherning has pointed out, "have proclaimed as certain what he himself with much reserve explained as probable,''1 but there has been no such unanimity of acceptance in this case as in that of the observations regarding the behavior of the images reflected from the lens. No one except the present writer, so far as I am aware, has ventured to question that the ciliary muscle is the agent of accommodation; but as to the mode of its operation there is generally felt to be much need for more light. Since the lens is not a factor in accommodation, it is not strange that no one was able to find out how it changed its curvature. It "is" strange, however, that these difficulties have not in any way disturbed the universal belief that the lens does change.
When the lens has been removed for cataract the patient usually appears to lose his power of accommodation, and not only has to wear a glass to replace the lost part, but has to put on a stronger glass for reading. A minority of these cases, however, after they become accustomed to the new condition, become able to see at the near-point without any change in their glasses. The existence of these two classes of cases has been a great stumbling block to ophthalmology. The first and more numerous appeared to support the theory of the agency of the lens in accommodation; but the second was hard to explain away, and constituted at one time, as Dr. Thomas Young observed, the "grand objection" to this idea. A number of these cases of apparent change of focus20 whose observations regarding the behavior of images reflected from the front of the lens are supposed to have demonstrated that the curvature of this body changes during accommodation in the lensless21 eye having been reported to the Royal Society by competent observers, Dr. Young, before bringing forward his theory of accommodation, took the trouble to examine some of them, and considered himself justified in concluding that an error of observation had been made. While convinced, however, that in such eyes the "actual focal distance is totally unchangeable," he characterized his own evidence in support of this view as only "tolerably satisfactory."
Fig. 12. Herman- Ludwig Ferdinand von Helmholtz (1821-1894)
At a later period Donders made some investigations from which he concluded that "in aphakial not the slightest trace of accommodative power remains."22 Helmholtz expressed similar views, and von Graefe, although he observed a "slight residuum" of accommodative power in lensless eyes, did not consider it sufficient to discredit the theory of Cramer and Helmholtz. It might be due, he said, to the accommodative action of the iris, and possibly also to a lengthening of the visual axis through the action of the external muscles.23 For nearly three-quarters of a century the opinions of these masters have echoed through ophthalmological literature. Yet it is to-day a perfectly well-known and undisputed fact that many persons, after the removal of the lens for cataract, are able to see perfectly at different distances without any change in their glasses. Every ophthalmologist of any experience has seen cases of this kind, and many of them have been reported in the literature.
In 1872, Professor Forster of Breslau, reported24 a series of twenty-two cases of apparent accommodation in eyes from which the lens had been removed for cataract. The subjects ranged in age from eleven to seventyfour years, and the younger ones had more accommodative power than the elder. A year later Woinow of Moscow25 reported eleven cases, the subjects being from twelve to sixty years of age. In 1869 and 1870, respectively, Loring reported26 to the New York Ophthalmological Society and the American Ophthalmological Society the case of a young woman of eighteen who, without any change in her glasses, read the twenty line on the Snellen test card at twenty feet and also read diamond type at from five inches to twenty. On October 8, 1894, a patient of Dr. A. E. Davis who appeared to accommodate perfectly without a lens consented to go before the New York Ophthalmological Society.
"The members," Dr. Davis reports,27 "were divided in their opinion as to how the patient was able to accommodate for the nearpoint with his distance glasses on"; but the fact that he could see at this point without any change in his glasses was not to be disputed.
The patient was a chef, forty-two years old, and on January 27, 1894, Dr.
Davis had removed a black cataract from his right eye, supplying him at the same time with the usual outfit of glasses, one to replace the lens, for distant vision, and a stronger one for reading. In October he returned, not because his eye was not doing well, but because he was afraid he might be "straining" it. He had discarded his reading glasses after a few weeks, and had since been using only his distance glasses. Dr. Davis doubted the truth of his statements, never having seen such a case before, but found them, upon investigation, to be quite correct. With his lensless eye and a convex glass of eleven and a half diopters, the patient read the ten line on the test card at twenty feet, and with the same glass, and without any change in its position, he read fine print at from fourteen to eighteen inches Dr. Davis then presented the case to the Ophthalmological Society but, as has been stated, he obtained no light from that source. Four months later, February 4, 1895, the patient still read 20/10 at the distance and his range at the near-point had increased so that he read diamond type at from eight to twenty-two and a half inches. Dr. Davis subjected him to numerous tests, and though unable to find any explanation for his strange performances, he made some interesting observations. The results of the tests by which Donders satisfied himself that the lensless eye possessed no accommodative power were quite different from those reported by the Dutch authority, and Dr. Davis therefore concluded that these tests were "wholly inadequate to decide the question at issue." During accommodation the ophthalmometer28 showed that the corneal curvature was changed and that the cornea moved forward a little. Under scopolamine, a drug sometimes used instead of atropine to paralyze the ciliary muscle (1/10 per cent solution every five minutes for thirty-five minutes, followed by a wait of half an hour), these changes took place as before; they also took place when the lids were held up. With the possible influence of lid pressure and of the ciliary muscle eliminated, therefore, Dr. Davis felt himself bound to conclude that the changes "must have been produced by the action of the external muscles." Under scopolamine, also, the man's accommodation was only slightly affected, the range at the nearpoint being reduced only two and a half inches.
The ophthalmometer further showed the patient to have absolutely no astigmatism. It had showed the same thing about three months after the operation, but three and a half weeks after it he had four and a half diopters.
Seeking further light upon the subject Dr. Davis now subjected to similar tests a case which had previously been reported by Webster in the "Archives of Pediatrics."29 The patient had been brought to -Dr. Webster at the age of ten with double congenital cataract. The left lens had been absorbed as the result of successive needlings, leaving only an opaque membrane, the lens capsule, while the right, which had not been interfered with, was sufficiently transparent around the edge to admit of useful vision. Dr. Webster made an opening in the membrane filling the pupil of the left eye, after which the vision of this eye, with a glass to replace the lens, was about equal to the vision of the right eye without a glass. For this reason Dr. Webster did not think it necessary to give the patient distance glasses, and supplied him with reading glasses only—plane glass for the-right eye and convex 16D for the left. On March 14, 1893, he returned and stated that he had been wearing his reading glasses all the time. With this glass it was found that he could read the twenty line of the test card at twenty feet, and read diamond type easily at fourteen inches. Subsequently the right lens was removed, after which no accommodation was observed in this eye. Two years later, March 16, 1895, he was seen by Dr. Davis, who found that the left eye now had an accommodative range of from ten to eighteen inches. In this case no change was observed in the cornea. The results of the Donders tests were similar to those of the earlier case, and under scopolamine the eye accommodated as before, but not quite so easily. No accommodation was observed in the right eye.
These and similar cases have been the cause of great embarrassment to those who feel called upon to reconcile them with the accepted theories. With the retinoscope the lensless eye can be seen to accommodate; but the theory of Helmholtz has dominated the ophthalmological mind so strongly that even the evidence of objective tests was not believed. The apparent act of accommodation was said not to be real, and many theories, very curious and unscientific, have been advanced to account for it. Davis is of the opinion that "the slight change in the curvature of the cornea, and its slight advancement observed in some cases, may, in those cases, account for some of the accommodative power present, but it is such a small factor that it may be eliminated entirely, since in some of the most marked cases of accommodation in aphakial eyes no such changes have been observed." The voluntary production of astigmatism is another stumbling block to the supporters of the accepted theories, as it involves a change in the shape of the cornea, and such a change is not compatible with the idea of an ''inextensible''30 eyeball. It seems to have given them less trouble, however, than the accommodation of the lensless eye, because fewer of these cases have been observed and still fewer have been allowed to get into the literature. Some interesting facts regarding one have fortunately been given by Davis, who investigated it in connection with the corneal changes noted in the lensless eye. The case was that of a house surgeon at the Manhattan Eye and Ear Hospital, Dr. C. H. Johnson. Ordinarily this gentleman had half a diopter of astigmatism in each eye; but he could, at will, increase this to two diopters in the right eye and one and a half in the left. He did this many times, in the presence of a number of members of the hospital staff, and also did it when the upper lids were held up, showing that the pressure of the lids had nothing to do with the phenomenon. Later he went to Louisville, and here Dr. J. M. Ray, at the suggestion of Dr. Davis, tested his ability to produce astigmatism under the influence of scopolamine (four instillations, 1/5 per cent solution). While the eyes were under the influence of the drug the astigmatism still seemed to increase, according to the evidence of the ophthalmometer, to one and a half diopters in the right eye and one in the left. From these facts, the influence of the lids and of the ciliary muscle having been eliminated, Dr. Davis concluded that the change in the cornea was "brought about mainly by the external muscles." What explanation others offer for such phenomena I do not know.
1 Johannes Kepler (1571-1630). German theologian. astronomer and physicist.Many facts of physiological optics were either discovered, or first clearly stated, by him.
2 Donders: On the Anomalies of Accommodation and Refraction of the Eye. English translation by Moore, 1864, p. 10. Frans Cornelis Donders (1818-1889) was professor of physiology and ophthalmology at the University of Utrecht, and is ranked as one of the greatest ophthalmologists of all time.
3 Edmund Landolt (1846-) Swiss ophthalmologist who settled in Paris in 1874, founding an eye clinic which has attracted many students.
4 On the Mechanism of the Eye, Phil. Tr. Roy. Soc., London, 1801.
5 On the Anomalies of Accommodation and Refraction of the Eye, pp. 10-11.
6 Maximilian Adolf Langenbeck (1518-1877). Professor of anatomy, surgery and ophthalmology at Gottingen, from 1846 to 1851. Later settled in Hanover.
7. Johannes Evangelista von Purkinje (1787-1869). Professor of physiology at Breslau and Prague, and the discoverer of many important physiological facts.
8. Antonie C. Cramer (1822-1855). Dutch ophthalmologist.
9. Handbuch der physiologischen Optik, edited by Nagel, 1909-11, vol. i, p. 121.
10. Ibid. vol. i, p. 122.
11. The Refraction and Accommodation of the Eye and their Anomalies, authorized translation by Culver, 1886, p. 151.
12. Physiologic Optics, authorized translation by Weiland, 1904, p. 163. Marius Hans Erik Tscherning (1854—) is a Danish ophthalmologist who for twenty-five years was co-director and director of the ophthalmological laboratory of the Sorbonne. Later he became professor of ophthalmology in the University of Copenhagen.
13. The Hygiene of the Eye in Schools, English translation edited by Turnbull, 1886, p. 23. Hermann Cohn (1838-1906) was professor of ophthalmology in the University of Breslau, and is known chiefly for his contributions to ocular hygiene.
14. Lessons in Elementary Physiology, sixth edition, 1872, p. 231.
15. On the Anomalies of Accommodation and Refraction of the Eye, p. 13.
16. Krankheiten des Auges, 1853-56, vol. iii, D. 219, et seq.
17. Ueber die Ursachen und die Entstehung der Kurzsichtigkeit, 1876. Vorwort.
18. Handbuch der physiologischen Optik, vol. i, pp. 124 and 145.
19. Ibid, vol. i. P. 144.
20. Physiologic Optics, p. 166.
21. Absence of the lens.
22. On the Anomalies of Accommodation and Refraction of the Eye, p. 320.
23. Archiv. f. Ophth., 1855, vol. ii, part 1, p. 187 et seq. Albrecht von Graefe (1828-1870) was professor of ophthalmology in the University of Berlin, and is ranked with Donders and Arlt as one of the greatest ophthalmologists of the nineteenth century.
24. Klin. Montasbl. f. Augenh., Erlangen, 1872, vol. x, p. 39, et seq.
25. Archiv. f. Ophth., 1873, vol. xix, part 3, p. 107.
26. Flint: Physiology of Man, 1875, vol. v, pp. 110-111.
27. Davis: Accommodation in the Lensless Eye, Reports of the Manhattan Eye and Ear Hospital, Jan., 1895. The article gives a review of the whole subject.
28. An instrument for measuring the curvature of the cornea.
29. Nov., 1893, p. 932.
30. Inasmuch as the eye is inextensible, it cannot adapt itself for the perception of objects situated at different distances by increasing the length of its axis, but only by increasing the refractive power of its lens.—De Schweinitz: Diseases of the Eye, eighth edition, 1916, pp. 35-36.
THE function of the muscles on the outside of the eyeball, apart from that of turning the globe in its socket, has been a matter of much dispute; but after the supposed demonstration by Helmholtz that accommodation depends upon a change in the curvature of the lens, the possibility of their being concerned in the adjustment of the eye for vision at different distances, or in the production of errors of refraction, was dismissed as no longer worthy of serious consideration. "Before physiologists were acquainted with the changes in the dioptic system,''1 says Donders, "they often attached importance to the external muscles in the production of accommodation. Now that we know that accommodation depends on a change of form in the lens this opinion seems scarcely to need refutation." He states positively that "many instances occur where the accommodation is wholly destroyed by paralysis, without the external muscles being the least impeded in their action," and also that "some cases are on record of paralysis of all or nearly all of the muscles of the eye, and of deficiency of the same, without diminution of the power of accommodation."2 If Donders had not considered the question settled, he might have inquired more carefully into these cases, and if he had, he might have been less dogmatic in his statements; for, as has been pointed out in the preceding chapter, there are plenty of indications that the contrary is the case. In my own experiments upon the extrinsic eye muscles of fish, rabbits, cats, dogs and other animals, the demonstration seemed to be complete that in the eyes of these animals accommodation depends wholly upon the action of the extrinsic muscles and not at all upon the agency of the lens. By the manipulation of these muscles I was able to produce or prevent accommodation at will, to produce myopia, hypermetropia and astigmatism, or to prevent these conditions. Full details of these experiments will be found in the "Bulletin of the New York Zoological Society" for November, 1914, and in the "New York Medical Journal" for May 8, 1915; and May 18, 1918; but for the benefit of those who have not the time or inclination to read these papers, their contents are summarized below. There are six muscles on the outside of the eyeball, four known as the "recti" and two as the "obliques." The obliques form an almost complete belt around the middle of the eyeball, and are known, according to their position, as "superior" and "inferior." The recti are attached to the sclerotic, or outer coat of the eyeball, near the front, and pass directly over the top, bottom and sides of the globe to the back of the orbit, where they are attached to the bone round the edges of the hole through which the optic nerve passes. According to their position, they are known as the "superior," "inferior," "internal" and "external" recti.- The obliques are the muscles of accommodation; the recti are concerned in the production of hypermetropia and astigmatism.
Fig. 13. Demonstration Upon the Eye of a Rabbit that the Inferior Oblique Muscle is an Essential Factor in Accommodation