Structure of the cone photoreceptor mosaic in the retinal periphery of adult humans: analysis as a function of age, sex, and hemifield

We have analyzed variation in the structure of the human photoreceptor mosaic as a function of age, sex, and retinal location using the nearest neighbor and density recovery profile methods. In contrast to most previous work, we have focused our analysis on the mid- and far-peripheral human retina. Video-enhanced differential interference contrast optics was used to characterize differences in the nasal and temporal periphery of unstained wholemounts from 12 males and 12 females ranging in age from 15- to 83-years-old. At sites matched for cone density (similar to 5,000 cones/mm(2)), the mosaic is far more orderly in the temporal than in the nasal periphery. This is true at all ages and in both sexes. Despite their increased local order, regularity ratios of adjacent temporal fields tend to be much more variable than are those of adjacent nasal fields. These marked nasal-temporal differences are eliminated when eccentricity is held constant and cone density is allowed to vary. There is a mild, statistically significant age-related decline in the regularity of the cone mosaic, but only in the nasal periphery. There are no significant differences in the precision of the cone mosaic between sexes. The equivalence of the regularity of the mosaic at matched eccentricities, but not at matched cone densities, suggests that the irregularity of the mosaic is secondary to developmental gradients and, more generally, to reduced selection for high acuity vision in the retinal periphery.