252 Prevention of Myopia
whose report of his study of the eyes of upwards of 10,000 children first called general attention to this sub ject, 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 percent ages, everywhere confirmed.
These conditions were unanimously attributed to the excessive use of the eyes for near work, though, accord ing to the theory that the lens is the agent of accommo dation, it was a little difficult to see just why near work should have this effect. On the supposition that accom modation 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 congen ital, were present, it has been supposed that the accom modative struggle for distinct vision produced irritation and strain which encouraged the production of short-
ml£««Mi£faCt*ry exPlanation of the mechanism by which near work produces myopia has not yet been given.-Tscherning: Physiologic Optics, p. 86.
nf ILIS £et utermmSl ho^ near work changes the longitudinal structure
of the eye.-Eversbusch: The Diseases of Children, vol. vi, p 291.