Binocular Vision

The Effect of Induced Prisms in Haploscopic Measurement of Fusional Limits

Abstract

When the haploscope is used to measure fusional limits at near, a -2.50 D lens is placed in a lens holder in front of each eye of the subject. It is assumed that the lines of sight will rotate equal amounts to the move­ment of the haploscope tubes such that the foveal fixation is maintained. This assumption is investigated. It was found that the lines of sight of 60% of the subjects studied lagged behind the movement of the arms of the haploscope. The implication of this is discussed and it is recom­mended that the haploscope be used as an instrument to train fusional vergences rather than to measure them.