Retinal contrast losses and visual resolution with obliquely incident light

To determine whether vision with obliquely incident light is degraded by contrast losses originating in the retina, laser interference fringe patterns were produced on the retina for various directions of incidence of the two interfering beams. Contrast-modulation flicker [Vision Res. 38, 985 (1998)] was used as a psychophysical measure of contrast at the level of the photoreceptors. Fringe contrast was shown to be maximal when the interfering beams were equal in perceived brightness, not in physical intensity. The effective fringe contrast was slightly reduced with oblique incidence for high spatial frequencies, but the reduction was too slight to be an important factor in visual resolution. The loss was similar whether the incident beams were displaced from the pupil center in a direction parallel or perpendicular to the grating bars.