Horopter deviations and distortions.

Previously gathered data from 3 subjects, judged to show usually very steady binocular fixation, were selected for retrospective analysis. This consisted of determining the means and standard error of the means of as many control runs as were available. The role of the fluctuation of vergence eye movement responses in producing the results is discussed. It is concluded that the longitudinal horopter most likely always conforms to the locus of a circle constructed through the two entrance pupils and the point of fixation.