What Is Amblyopia?

Abstract

Amblyopia is defined primarily as a loss of acuity. In anisometropia, grating acuity, Snellen (optotype) acuity, and vernier acuity are degraded in proportion to each other. In strabismus, Snellen and vernier acuity are degraded more than grating acuity. The main problem in both cases is loss of binocular function, producing loss of stereoscopic vision. A number of other properties are also affected. There is uncertainty about the location of an object in space, a reduction in the ability to detect shapes, deficits in motion and direction perception, less ability to track several objects at once, reduced counting ability, and suppression of the image in one eye by the image in the other, to avoid the diplopia and confusion arising when the two eyes are looking in different directions. Some of these deficits are seen in the fellow as well as the amblyopic eye and in binocular viewing. There are also deficits in eye movements: poor fixation, a longer latency for saccades, inability to follow an object moving away from the nose smoothly, and slow inaccurate movements in visually guided reaches. These particularly affect reading so that an amblyope’s reading speed in both eyes is one-half to three-quarters of that of a normal person.