Effects of aging on the densities, numbers, and sizes of retinal ganglion cells in rhesus monkey.

We used sterological procedures that yield unbiased estimates to quantify the densities, numbers, and soma sizes of retinal ganglion cells in seven young adult and six old rhesus monkeys. The retinae were flat mounted so that we could determine whether there are different aging-related losses in different retinal regions. The mean (+/-standard deviation) total number of ganglion cells was 1,529,039 +/- 115,260 in young-adult retinae and 1,556,698 +/- 165,056 in old retinae, a difference that was not statistically significant. There also were no significant differences between young and old retinae in the densities or total numbers of ganglion cells in the four retinal quadrants, in four concentric retinal zones from fovea to peripheral retina, or in smaller hemiretinal regions of the concentric zones. Ganglion-cell soma sizes also did not differ significantly between young and old animals. Moreover, counts of the largest ganglion cells, which probably correspond to P alpha ganglion cells, revealed no selective loss of these cells with aging. These results are consistent with our previous anatomical and physiological studies of the LGN. Together they suggest that the retino-geniculate pathways are relatively unaffected by aging in the rhesus monkey.