Effect Of Distance Fixation Disparity On Distance Stereopsis As Compared Among Individuals With Superior Visual Systems.

Stereopsis and fixation disparity (FD) were measured at a distance of 6 meters on 10
patients who exhibited very small amounts of vertical and horizontal heterophoria as well as excellent visual acuity (20/20). The amount of FD was then increased by stressing the visual system with base-in (BI) prism insertion. As FD increased for each individual patient, their ability to appreciate stereopsis at 6 meters was reduced. By selecting patients with normal systems, we isolated the results to only FD and its effect on stereopsis. This study proved that as FD increased, stereo acuity decreased and suggests that FD rather than heterophoria poses the threat to stereopsis.