Abstract

The cone entrance aperture is thought to be located in the inner segment. Little is known about changes in cone inner segment diameter (CISD) across the entire human retina. The degree to which the increase in CISD with eccentricity offsets decline in cone density to maintain total quantal flux per unit retinal area is unknown. Gradients in refractive index along the length of CIS were viewed directly in cleared retinal whole mounts using Normarski differential interference contrast microscopy. Individual CISs are optically resolvable from their neighbors at a level slightly vitreal to the CIS ellipsoid–myoid junction. CISD at this presumed aperture level and the proportion of retinal area occupied by apertures a_a were measured from the fovea of one and the periphery of four young adult retinas previously mapped for cone density. CISD increased sharply from 2.3 μm at the foveal center to 6.5 μm at 1 mm (3.6°) and slowly from there to a maximum of 8.5–9 μm near the ora serrata. a_a decreased approximately threefold across the retina from 69 to 78% in the foveola to a plateau of 20–35% in the midperiphery to far periphery. Over this eccentricity range, the cone density declined fortyfold. These results predict different eccentricity dependencies for visual functions explained by the density of cones and those explained by the number of photons available to cone photopigment.

© 1987 Optical Society of America