On spectacles : their history and their uses / by Professor Horner.

  • Johann Friedrich Horner
Date:
1887
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Licence: Public Domain Mark

Credit: On spectacles : their history and their uses / by Professor Horner. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    of the short-sighted, i.e., that he can see normally with the correcting concave glass, the choice of the glass is difficult in the case of young persons and in increasing myopia for many reasons. We must indicate these more precisely. In young persons who during their school career require concave spectacles, in about 35 per cent, too strong spectacles will probably be chosen, if those spectacles are ordered with which, e.g., a boy of fourteen says he sees distant objects best, for they are adapted not only to the length of the eye, but to the constant tension of the accommodation in addition. Therefore the objec- tive myopia should always be ascertained by means of the ophthalmoscope, and the very weakest spectacles that enable him to see distant objects selected. The spectacles needful for distance, as also for the black-board, maps, &c, are only innocuous for near work (writing, &c.) when the wearer adopts the position that a normal-sighted person ought to assume. If he bends down his head as before, the spectacles do him harm ; his short-sightedness then increases more rapidly, and he has to increase the strength of his spectacles quickly. It is difficult to obtain a statistical proof of this in spite of the frequency of individual experience. He who, using the spectacles for distance, brings his fine work as close to his eyes as before wearing spectacles—and this is what is usually done by boys and girls — puts on the full power of his accommodation screw, and thereby sets in action the mechanism which is chiefly instrumental in the production and increase of myopia. Hence concave spectacles, even when rightly selected for distant vision, may prove a danger instead of an improvement ; therefore school- children ought not to be so often required to wear spec- tacles, if, for instance, they are able to see the figures on the black-board, when these are made somewhat larger than usual.
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