Twenty minutes' advice on the eyes, and the means of preserving the sight ... together with the right time for using glasses, and the choice of them / By a retired oculist.

Date:
1834
Catalogue details

Licence: Public Domain Mark

Credit: Twenty minutes' advice on the eyes, and the means of preserving the sight ... together with the right time for using glasses, and the choice of them / By a retired oculist. Source: Wellcome Collection.

    21/64 (page 17)
    West Indies, and whose sight when he was young enabled him to see both near and distant objects with great precision, began at the age of forty to experience a difficulty in reading and writing. He immediately procured convex spectacles of the first number sold by opticians, which glasses are usually ground to a focus of forty-six or forty-eight inches, and by the aid of these he continued to read and write with ease (distinguishing perfectly in the usual way all distant objects without them), until he was fifty. At this time he first began to perceive an indistinctness in the appearance of things at a distance, and on trying with different glasses he discovered that by looking through a double concave glass of the sixth number (which is ground to a radius of eight inches on one side and eleven inches on the other), he was enabled to see distant objects distinctly. He has continued to use glasses of this description for the purpose of seeing distant objects from that time to the present, but is obliged to remove them whenever he reads, and still to employ the first number of a convex glass. In this instance, a presbyopic was changed to a myopic sight without any known efficient circumstances to produce it. There are many other cases in which a similar change took place, but in them it was attributable to known causes. c