Myopia (commonly called near-sightedness,) in its various phases / by Julian J. Chisholm.

  • Chisolm, Julian John, 1830-1903.
Date:
[1880]
Catalogue details

Licence: Public Domain Mark

Credit: Myopia (commonly called near-sightedness,) in its various phases / by Julian J. Chisholm. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    •error has never been corrected. The junior members of the pro- fession who have recently pursued their medical studies in the large cities, have had better advantages for obtaining an insight into the specialties in medicine. They have been taught that in most near-sighted eyes there is an elongation in the long diame ter of the eye from the pupil backwards, and not in the increased convexity of the cornea. There is to be sure a rare form of near-sightedness in which the elongation of the eye is due exclu- sively to the protrusion forwards of the cornea, the centre of which projects outwards as a cone—a disease called conical cornea. This pathological condition is, however, so very rare that it would mot explain one case of near-sightedness out of one thousand. Where a perfect eye has become myopic, the elongation of the eye-ball is usually found in the bulging of the back wall or scle- rotic coat near the entrance of the optic nerve, and to which the most elaborated portions of the retina, with choroidal backing, is attached. This explanation, viz : the pushing out of the back wall of the eye-ball, which is applicable to the majority of adult near-sighted persons, does not, however, cover the entire field of myopia. Some old persons, markedly near sighted, whose sharp vision extends to a very few feet, have experienced no change whatever in the length of this ocular diameter. In this small class of myopes an explanation of the optical defect is found in the change of shape in the lens alone. Again, in a very large number of young persons who have restricted distant vision, near-sightedness is found associated with an eye that is actually shorter in this antero-posterior diameter than a good eye should be. It is in the act of habitually straining such a flat eye to make it see sharply small, near objects, that the ciliary or accommodating muscles within the eye-ball become irritable, and finally are thrown into a spasmodic contraction, with inability to resume voluntarily a passive or relaxed state. It is this excessive muscular contraction, continuously kept up, which makes the lens too convex, shortens its focus, and puts an end to distant vision, by blurring the definition of objects across the street, and induces near sishtedness.