Optical and neural resolution in peripheral vision.

Visual acuity along the horizontal meridian in the peripheral field of vision was determined at a photopic level in two normal subjects. Two types of sinusoidally modulated, monochromatic test patterns of high contrast were used. One was produced directly on the retina by an interferometric technique. The other type was imaged on the retina by the dioptric apparatus of the eye; the resulting image suffered ordinary optical image degradation. The results from the interferometric acuity determinations represent maximal neural discrimination across the visual field. Acuity decreases monotonically toward the periphery, from about 45 cycles per degree in the fovea, to about 0.8 at 80 degrees of eccentricity in the temporal field. The decline is well described by a second-degree polynomial. Acuity for test patterns imaged by the optics of the eye was consistently lower than interferometric acuity. The difference increases toward the periphery. It is attributable to effects of optical aberrations. The discrepancy between optical and neural resolving power on oblique incidence needs to be taken into account whenever results obtained with external, extra-axial stimuli are to be analyzed in terms of retinal architecture.