Directional sensitivity of the foveal and parafoveal retina.

Photopic directional sensitivity was measured at the fovea and at 2°, 3.75°, and 10° from fixation (referred to the center of the entrance pupil of the eye; nonfoveal tests were conducted in the nasal field projected onto temporal retina). These data confirm and extend an earlier experiment performed by Westheimer. The central fovea exhibited significantly less directionality than parafoveal test points. Differences in directionality between the three parafoveal test loci were not significant. Possible factors giving rise to the foveal-parafoveal difference in directionality are reviewed. Evidence corroborating our earlier observations that receptors across the retina are aligned with the point approximating the center of the exit pupil of the eye is also presented.