On the Importance of a Proper Selection of Spectacles
Hasket Derby · New England Journal of Medicine · 1862
It is my intention, in this paper, to draw attention to a condition of the eye requiring the use of glasses, that has not-to the best of my knowledge-been alluded to in any work on ophthalmology in the English language, till within the past few months ; though, for several years, it has engrossed the attention of German winters in this department.Short sight and old sight, myopia and presbyopia, have been the two grand heads to which, from time immemorial, all anomalies of the refractive powers of the eye have been referred.If a person could not see well at a distance, and was moreover obliged to bring all near objects close to the eye, in order to obtain a full view of them, such a one was regarded as myopic, and if concave glasses failed to relieve him or improve his vision, the convenient term of amblyopia would be called in to explain such an apparent deviation from the general rule.And the term presbyopia was understood to refer to an opposite class of cases, where, with advancing years, the object was obliged to be held at a greater distance from the eye to ensure distinctness of vision, and convex glasses must be used to remedy this inconvenience.Myopia was supposed to be caused by an increase of the power of refraction of the eye, or a lengthening of its antcro-posterior axis; so that the images, instead of being formed on the retina, fell in front of it.And in presbyopia, owing to what was understood to be an opposite condition of things, the images could only be formed behind the retina.The fact, now well understood, that myopia and presbyopia may co-exist in the same subject ; that a person, moderately myopic and employing a concave glass for distant objects, may, as he advances in life, be forced to use a convex glass for the near, while he continues to use the same lens as before for other purposes, is of itself asufficient refutation of the old theory.