No phase of ophthalmology, not even the problem of accommodation, has been the subject of so much investigation and discussion as the cause and prevention of myopia. Since hypermetropia was supposed to be due to a congenital deformation of the eyeball, and astigmatism, until recently, was also supposed to be congenital in most cases, these conditions were not thought to call for any explanation, nor to admit of any prevention; but myopia appeared to be acquired. It therefore presented a problem of immense practical importance to which many eminent men devoted years of labor.
Voluminous statistics were collected regarding its occurrence, and are still being collected. The subject has produced libraries of literature. But very little light is to be gained from the perusal of this material, and for the most part it leaves the reader with an impression of hopeless confusion. It is impossible even to arrive at any conclusion as to the prevalence of the complaint; for not only has there been no uniformity of standards and methods, but none of the investigators has taken into account the fact that the refraction of the eye is not a constant condition, but one which continually varies. There is no doubt, however, that most children, when they begin school, are free from this defect, and that both the number of cases and the degree of the myopia steadily increase as the educational process progresses. Professor Hermann Cohen, of Breslau, whose report of his study of the eyes of upwards of 10,000 children first called general attention to this subject, found scarcely one per cent of myopia in the village schools, twenty to forty per cent in the Realschulen, thirty to thirty-five in the gymnasia, and fifty-three to sixty-four in the professional schools. His investigations were repeated in many cities of Europe and America, and his observations, with some difference in percentages, everywhere confirmed.
These conditions were unanimously attributed to the excessive use of the eyes for near work, though, according to the theory that the lens is the agent of accommodation, it was a little difficult to see just why near work should have this effect. On the supposition that accommodation was effected by an elongation of the eyeball, it would have been easy to understand why an excessive amount of accommodation should produce a permanent elongation. But why should an abnormal demand on the accommodative power of the lens produce a change, not in the shape of that body, but in that of the eyeball? Numerous answers to this question have been proposed, but no one has yet succeeded in finding a satisfactory one.(1) In the case of children it has been assumed by many authorities that, since the coats of the eye are softer in youth than in later years, they are unable to withstand a supposed intraocular tension produced by near work. When other errors of refraction, such as hypermetropia and astigmatism, believed to be congenital, were present, it has been supposed that the accommodative struggle for distinct vision produced irritation and strain which encouraged the production of short sight. When the condition developed in adults, the explanations had to be modified to fit the case, and the fact that a considerable number of cases were observed among peasants and others who did not use their eyes for near work led some authorities to divide the anomaly into two classes, one caused by near work and one unrelated to it, the latter being conveniently attributed to hereditary tendencies.
As it was impossible to abandon the educational system, attempts were made to minimize the supposed evil effects of the reading, writing and other near work which it demanded. Careful and detailed rules were laid down by various authorities as to the sizes of type to be used in schoolbooks, the length of the lines, their distance apart, the distance at which the book should be held, the amount and arrangement of the light, the construction of the desks, the length of time the eyes might be used without a change of focus, etc. Face-rests were even devised to hold the eyes at the prescribed distance from the desk and to prevent stooping, which was supposed to cause congestion of the eyeball and thus to encourage elongation. The Germans, with characteristic thoroughness, actually used these instruments of torture, Cohn never allowing his own children to write without one, “even when sitting at the best possible desk.”(2)
The results of these preventive measures were disappointing. Some observers reported a slight decrease in the percentage of myopia in schools in which the prescribed reforms had been made, but on the whole, as Risley has observed in his discussion of the subject in Norris and Oliver’s System of Diseases of the Eye, “the injurious results of the educational process were not notably arrested.”
Cohn never allowed his children to write without it, even when sitting at the best possible desk.
“It is a significant, though discouraging, fact,” he continues, “that the increase, as found by Cohn both in the percentage and in the degree of myopia, had taken place in those schools where he had especially exerted himself to secure the introduction of hygienic reforms; and the same is true of the observations of Just, who had examined the eyes of twelve hundred and twenty-nine of the pupils of the two high schools of Zittau, in both of which the hygienic conditions were all that could be desired. He found, nevertheless, that the excellent arrangements had not in any degree lessened the percentage of increase in myopia.”(3)
Further study of the subject has only added to its difficulty, while at the same time it has tended to relieve the schools of much of the responsibility formerly attributed to them for the production of myopia. As the American Encyclopedia of Ophthalmology points out, “the theory that myopia is due to close work aggravated by town life and badly lighted rooms is gradually giving ground before statistics.”(4)
In an investigation in London, for instance, in which the schools were carefully selected to reveal any differences that might arise from the various influences, hygienic, social and racial, to which the children were subjected, the proportion of myopia in the best lighted building of the group was actually found to be higher than in the one where the lighting conditions were worst, although the higher degrees of myopia were more numerous in the latter than in the former. It has also been found that there is just as much myopia in schools where little near work is done as in those in which the demand upon the accommodative power of the eye is greater.(5) It is only a minority of children, moreover, that become myopic; yet all are subject to practically the same influences, and even in the same child one eye may become myopic while the other remains normal. On the theory that shortsight results from any external influence to which the eye is exposed it is impossible to account for the fact that under the same conditions of life the eyes of different individuals and the two eyes of the same individual behave differently.
Owing to the difficulty of reconciling these facts on the basis of the earlier theories, there is now a growing disposition to attribute myopia to hereditary tendencies;(6) but no satisfactory evidence on this point has been brought forward, and the fact that primitive peoples who have always had good eyesight become myopic just as quickly as any others when subjected to the conditions of civilized life, like the Indian pupils at Carlisle,(7) seems to be conclusive evidence against it.
In spite of the repeated failure of preventive measures based upon the limitation of near work and the regulation of lighting, desks, types, etc., the use of the eyes at the nearpoint under unfavorable conditions is still admitted by most exponents of the heredity theory as probably, if not certainly, a secondary cause of myopia. Sidler-Huguenin, however, whose startling conclusions as to the hopelessness of controlling shortsight were quoted earlier, has observed so little benefit from such precautions that he believes a myope may become an engineer just as well as a farmer, or a forester; and as a result of his experiences with anisometropes, persons with an inequality of refraction between the two organs of vision, he even suggests that the use of myopic eyes may possibly be more favorable to their well-being than their non-use. In 150 cases in which, owing to this inequality and other conditions, the subjects practically used but one eye, the weaker organ, he reports, became gradually more and more myopic, sometimes excessively so, in open defiance of all the accepted theories relating to the matter.
The prevalence of myopia, the unsatisfactoriness of all explanations of its origin, and the futility of all methods of prevention, have led some writers of repute to the conclusion that the elongated eyeball is a natural physiological adaptation to the needs of civilization. Against this view two unanswerable arguments can be brought. One is that the myopic eye does not see so well even at the near point as the normal eye, and the other that the defect tends to progression with very serious results, often ending in blindness. If Nature has attempted to adapt the eye to civilized conditions by an elongation of the globe, she has done it in a very clumsy manner. It is true that many authorities assume the existence of two kinds of myopia, one physiological, or at least harmless, and the other pathological; but since it is impossible to say with certainty whether a given case is going to progress or not, this distinction, even if it were correct, would be more important theoretically than practically.
Into such a slough of despond and contradiction have the misdirected labors of a hundred years led us ! But in the light of truth the problem turns out to be a very simple one. In view of the facts given in Chapters V and IX, it is easy to understand why all previous attempts to prevent myopia have failed. All these attempts have aimed at lessening the strain of near work upon the eye, leaving the strain to see distant objects unaffected, and totally ignoring 4 the mental strain which underlies the optical one. There are many differences between the conditions to which the children of primitive man were subjected, and those under which the offspring of civilized races spend their developing years, besides the mere fact that the latter learn things out of books and write things on paper, and the former did not. In the process of education civilized children are shut up for hours every day within four walls, in the charge of teachers who are too often nervous and irritable. They. are even compelled to remain for long periods in the same position. The things they are required to learn may be presented in such a way as to be excessively uninteresting; and they are under a continual compulsion to think of the gaining of marks and prizes rather than the acquisition of knowledge for its own sake. Some children endure these unnatural conditions better than others. Many cannot stand the strain, and thus the schools become the hotbed, not only of myopia, but of all other errors of refraction.
1. A satisfactory explanation of the mechanism by which near work produces myopia has not yet been given. – Tscherning: Physiologic Optics, p. 86
It is not yet determined how near work changes the longitudinal structure of the eye. – Eversbusch: The Diseases of Children, vol. vii, p. 291.
2. The Hygiene of the Eye in Schools, p 127.
3. School Hygiene, System of Diseases of the Eye, vol. ii, p. 361.
4. American Encyclopedia and Dictionary of Ophthalmology, edited by Wood, 1913-1919, vol. xi, p. 8271.
5. Lawson: Brit. Med. Jour., June 18, 1898.
6. It seems to have been amply demonstrated, by the studies of Motais, Steiger, Miss Barrington, and Karl Pearson, that errors of refraction are inherited. And while the use of the eyes for near work is probably a secondary cause, determining largely the development of the defects it is not the primary cause. – Cyclopedia of Education, edited by Monroe, 1911-1913.
7. Fox (quoted by Risley): System of Diseases of the Eye, vol. ii, p. 357.