Analysis of Human Receptor Density

Data for densities and sizes of human cones were analyzed as a function of retinal eccentricity. Density of cones followed a decreasing power of about -2/3 over much of the eccentricity range. This decrease, and the subsequent increase in cone density toward the ora serrata, were predictable on the basis of a hypothetical density-control mechanism to equate the integrated luminous flux at the photoreceptors per unit retinal area, together with the empirical rule that cone diameter increases with a power of about 1/3 with eccentricity beyond the foveola. The analysis implies that cones aggregate in inverse proportion to the light impinging on them, and provides an explanation for the pronounced increase to 100% cone density at the ora serrata.