AGING OF THE HUMAN PHOTORECEPTOR MOSAIC - EVIDENCE FOR SELECTIVE VULNERABILITY OF RODS IN CENTRAL RETINA

Purpose. Because previous studies suggested degeneration and loss of p hotoreceptors in aged human retina, the spatial density of cones and r ods subserving the central 43-degrees of vision as a function of age w as determined. Methods. Cones and rods were counted in 27 whole mounte d retinas from donors aged 27 to 90 years with macroscopically normal fundi. Photoreceptor topography was analyzed with new graphic and stat istical techniques. Results. Changes in cone density throughout this a ge span showed no consistent relationship to age or retinal location, and the total number of foveal cones was remarkably stable. In contras t, rod density decreased by 30%, beginning inferior to the fovea in mi dlife and culminating in an annulus of deepest loss at 0.5 to 3 mm ecc entricity by the ninth decade. Space vacated by dying rods was filled in by larger rod inner segments, resulting in a similar rod coverage a t all ages. At the temporal equator, cone density declined by 23%, but rods were stable throughout adulthood. Conclusions. The stability of both rod coverage and rhodopsin content despite decreasing cell number suggests plasticity of the adult rod system and that age-related decl ines in scotopic sensitivity may be due to postreceptoral factors. The re is no evidence for the massive loss of foveal cones required to exp lain even modest decrements in acuity, consistent with evidence that v isual deficits at high photopic levels may be largely due to optical f actors. Why the rods of central retina, which share a common support s ystem and light exposure with the neighboring cones, are Preferentiall y vulnerable to aging remains to be determined.