Simultaneous measurement of two-point-spread functions at different locations across the human fovea.

An experimental system for measuring simultaneously the retinal images of two-point tests has been developed. In particular we present one experiment in which one of the points is located at the center of the fovea and the other one is at 1 deg of eccentricity. At these two foveal locations the optical image quality is expected to be approximately the same, while the structure of the retina is known to be quite different. Our results of aerial images show small but systematic differences between the two-pointspread functions that are measured at 0 and 1 deg of eccentricity. The image quality is always slightly better in the center of the fovea with the differences more marked in the nasal and inferior orientations. That could be explained by a small but noticeable contribution of the retinal thickness to the optical aberrations of the eye. The possible increment of scattering caused by the increase in retinal thickness at 1 deg was barely measurable in our experiment. An indirect consequence is that retinal reflection has little practical influence on our particular double-pass measurements of the eye's image quality.