Retinoscopy (or shadow test) in the determination of refractions at one meter distance, with the plane mirror / by James Thorington.

  • Thorington, James, 1858-1944.
Date:
1906
Catalogue details

Licence: In copyright

Credit: Retinoscopy (or shadow test) in the determination of refractions at one meter distance, with the plane mirror / by James Thorington. Source: Wellcome Collection.

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    retina immediately surrounding the illumination. The retinal illumination and shadow are, therefore, in contact, and the contrast in most marked and easily recognized when the refractive error is a moderately high one, two or three diopters. It is by this combination of the illu- mination and non-illumination (shadow) that we study and give the “shadow test” its name. In the dark room, the patient keeping his eye fixed, the retina is stationary and in total darkness, except the portion illuminated by the light from the mirror (see Fig. 14). If the mirror be rotated the retinal illumination changes its place (see Fig. 15) and darkness, or shadow, appears in its stead. It is by this change of shadow (darkness) for illumination that we often speak of a movement of the shadow. Where to Look and What to Look For.—With the patient, the observer, and the source of light in position as directed, the rays of light are reflected into the eye from the mirror as it is gently rotated in the various meridians, and the (1) form, (2) direction, and (3) rate 0] movement of the retinal illumination are carefully noted through a four- or five-millimeter area at the apex oj the cornea, as this is the part of the refractive media in the normal eye that the patient will use when the effects of the cycloplegic pass away and the pupil regains its normal size. The one- or two-millimeter area at the edge of the pupil should be avoided by the beginner, except in special in- stances, as only too frequently it contains a bright ring of light which may or may not give a stronger refraction than the 4-millimeter area about the apex of the cornea (see Spheric Aberration, chap. VI). The beginner will do good work with the retinoscope if he observes closely the illumination at the center of the pupil and avoids looking for shadows.