Eyesight, and how to care for it / edited by George Black.

Date:
[1888]
Catalogue details

Licence: Public Domain Mark

Credit: Eyesight, and how to care for it / edited by George Black. Source: Wellcome Collection.

    81/168 (page 77)
    troubles — obvious enough, now that a master mind has pointed out the way to us — is to use the convex glass (Fig. VIII.) that will give to parallel rays of light the necessary degree of convergence before they enter the eye. The muscle of accommodation is thus re- lieved of its extra work, the focus is brought forward on to the retina, and the focal distance of the eye and the glass together is according to measure. Short-sight has for many years been called myopia, from two Greek words meaning to close the eye, be- cause short-sighted persons have the habit of half- closing the lids in the effort to see distinctly; and this term has been retained by modern authors. Fig. XVII. —Myopia. While in the perfectly formed or emmetropic eye the focus for parallel rays of light falls accurately upon the retina, and in the hypermetropic eye falls beyond it, in myopia it falls in front of the retina. In hy- permetropia the axis of the eyeball is shorter than the focal distance for parallel rays, and only conver-