Prism-induced horopter distortions.

The effects that lateral prisms have on the horopter were evaluated in 11 subjects, including 6 subjects classified as binocularly abnormal. For normal subjects with good stereopsis the equidistance (stereoscopic distance matching) horopter shape was altered with the application of lateral prism. For other subjects this was not the case. Equidirection (nonius) horopters were unchanged by the application of lateral prism in all of the subjects tested. In addition to localized irregularities in the horopter locus, shifts in fixation disparity produced regional distortions of the horopter.