The determination of the necessity for wearing glasses / by D.B. St. John Roosa.

  • Roosa D. B. St. John (Daniel Bennett St. John), 1838-1908.
Date:
1887
Catalogue details

Licence: Public Domain Mark

Credit: The determination of the necessity for wearing glasses / by D.B. St. John Roosa. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

    13/96
    History of the arrangement of test-types as scientific tests of visual power.— The invention of the oph- thalmoscope made it possible to measure the refrac- tion of the eye.—How glasses were formerly chosen. —Donders on Accommodation and Refraction. — Apparatus required for testing vision.— Classifica- tion of conditions requiring glasses. It was not until the year 1854, that any systematic attempt was made by the medical profession to accu- rately estimate the visual power. During this year, Alfred Smee, in England, and Eduard Jaeger, in Austria, published a set of test-letters, or test-types for this purpose. These tests were convenient, but in- sufficient. They consisted merely of a collection of paragraphs in type, ranging from the finest that is made, to very large letters, such as are used in hand- bills. They gave no idea as to how far each size should be seen by a normal eye, and beyond the statement of the ability of the patient to read fine or coarse type fluently or slowly, it was not possible with them—valuable as they were, and still are—to give an exact idea of the visual power of a given person. In 1868, Snellen, of Holland, published a set of test- types, which virtually showed the problem of register- ing vision. Snellen’s types are founded upon the principle of determining the smallest angle in which the * ;