The Effects Of Vergence Demand And Fixation Disparity On Stereopsis.

Although forced vergence is known to effect fixation disparity, studies on the effects of vergence demand on stereopsis and the relationship between fixation disparity and depth perception have been mostly inconclusive. This study was designed to nvestigate the hypothesis that stereopsis breaks down as vergence demand causes fixation disparity to exceed Panum's tusional area. A novel computer software application which generates anaglyph targets to separately measure tixation disparity and stereopsis under forced vergence conditions is used with a z-100 Zenith microcomputer. Thirty-nine subjects with normal binocularity were tested. The highly variable results show a definite reduction of depth perception at the extremes of the fusional range. A correlation between stereopsis and fixation disparity is not clearly demonstrated. Only minor decreases in stereopic performance are observed in some subjects despite relatively large fixation disparity values for the same vergence demand, suggesting that stereopsis is a more deeply ingrained binocular function. A critique of the methods used in this investigation is included, with areas of possible improvement pointed out and refinements suggested.