Abstract

Several researchers have measured threshold visual acuity at different retinal eccentricities using different methodologies and field sizes and have produced strikingly different results. To address these differences, we measured interference fringe (grating) acuity in the foveal and parafoveal retina using laser interferometry, employing both two-alternative forced-choice discrimination of grating orientation and method of limits (grating appearance) methodologies. Our forced-choice results at 2-deg retinal eccentricity yield orientation discrimination thresholds which are approximately 2 cycles/deg less for 0.6-deg vs 2-deg test fields. However, no difference was found between results with 0.6- and 2-deg test fields at 4-deg eccentricity. This pattern of results holds for two observers tested. While the results vary with field size, estimates of orientation discrimination threshold produced under forced-choice conditions well approximate the theoretical Nyquist limit.

© 1988 Optical Society of America