The relationship between visual resolution and cone spacing in the human fovea

Abstract

Visual resolution decreases rapidly outside of the foveal center. The anatomical and physiological basis for this reduction is unclear. We used simultaneous adaptive optics imaging and psychophysical testing to measure cone spacing and resolution across the fovea, and found that resolution was limited by cone spacing only at the foveal center. Immediately outside of the center, resolution was worse than cone spacing predicted and better matched the sampling limit of midget retinal ganglion cells.

Figure 1. Cone stimulation map for subject S3

Cones appear as bright circles arranged in a triangular lattice pattern. Stimulated cones are shown as topographic maps overlaid in color. Color bar shows normalized level of cone stimulation.

Figure 2. Visual resolution matches the Nyquist limit of the mRGC mosaic, not the cone Nyquist limit

a, Visual acuity as a function of eccentricity. Symbol legend is inset in (d). For observer S4, t, n, s, and i denote temporal, nasal, superior and inferior locations. Error bars are ± s.e.m. and omitted when smaller than symbol. b, Cone Nyquist limit across the horizontal temporal retina. Lines colored by subject in the same way as symbols (see legend inset). Solid lines are measurements; dashed lines are predictions. c, Cone Nyquist limit and MAR for temporal test locations. Cone Nyquist limit is mean of cones within an elliptical area subtending ± 2SD of mean stimulated location. Error bars are ± s.e.m. and omitted when smaller than symbol. Dashed black line is the 1:1 line. d, Nyquist limit of mRGC and MAR. Only results along horizontal meridian are shown for S4. Dashed black line is the 1:1 line.