<title>Packing geometry of human cone photoreceptors: variations with eccentricity and evidence for local anisotropy</title>

Abstract

Disorder in the packing geometry of the human cone mosaic is believed to help alleviate spatial aliasing effects. In order to characterize cone packing geometry we gathered positions of cone inner segments at 7 locations along 4 primary and 2 oblique meridians in an adult human retina. We generated statistical descriptors based on the distribution of distances and angles to Voronoi neighbors. Parameters of a compressed-jittered model were fit to the actual mosaic. Local anisotropies were investigated using correlograms. We find that: (1) median distance between Voronoi neighbors increases with eccentricity, but the minimum distance is constant (6-8 micrometers ) across peripheral retina; (2) the cone mosaic is most orderly at the edge of the foveal rod-free zone; (3) in periphery, cone spacing is 10-15% less in one direction than in the orthogonal direction; (4) cone spacing is minimal perpendicular to meridians emanating from the foveal center. The nearly constant minimum distance implies that high spatial frequencies may be sampled even in peripheral retina. Local anisotropy of the cone mosaic is qualitatively consistent with the meridional resolution effect previously described for the discrimination of gratings.