A manual of diseases of the eye / by Charles H. May and Claud Worth.

  • May, Charles Henry, 1861-1943.
Date:
1924
Catalogue details

Licence: Public Domain Mark

Credit: A manual of diseases of the eye / by Charles H. May and Claud Worth. Source: Wellcome Collection.

    23/524 (page 9)
    CHAPTER II SUBJECTIVE OR FUNCTIONAL EXAMINATION OF THE EYE The subjective examination, dependent upon the statements of the patient, comprises the testing of the function (sight) of each eye separately. This function may be subdivided into (i) the form sense, (2) the colour sense; and (3) the light sense. The form sense is the faculty which the eye possesses of perceiving the shape or form of objects, and is expressed as acuteness of vision. The colour sense is the power which the eye has of distinguishing light of different wave lengths—i.e., distinguishing colours. The light sense is the faculty of perceiving different degrees of intensity of illumination (brightness). We distinguish between central and peripheral vision. The Acuteness of Vision. Central or Direct Vision.—When we wish to see an obiect j clearly, we look directly at it so that the image falls upon the macula lutea, the portion of the retina which is adapted for the most acute vision. The acuteness should be tested both for distant and for near vision. Distant Vision.—In testing for distance a range of 20 feet (6 metres) is selected, since rays of light from a point at this distance are nearly parallel. For this purpose we make use of Snellen's test types, which are constructed upon the following principle: Each letter is inscribed within a square (Fig. 12), which sub tends a visual angle of 5' at the distance at which