Morphometric Analysis of Retinal Ganglion Cells in Spontaneously Diabetic Monkeys

Abstract

Abstract: : Purpose: The extent of ganglion cell pathology in diabetic retinopathy is controversial. In this study, we evaluated ganglion cell loss in rhesus monkeys that spontaneously developed type 2 diabetes mellitus. These monkeys develop the same complications of diabetes as humans, including retinopathy. Methods: Fifteen retinas were collected from four age–similar normoglycemic and 11 diabetic monkeys and prepared for JB4 embedding after being incubated for ADPase activity to demonstrate viable blood vessels. Retinal sections were cut 2.5 um in thickness and stained with PAS–hematoxylin or thionin–ammonium sulfide (develops ADPase reaction product). Ganglion cells were counted in all retinas under 40X magnification in at least two areas: three nasal contiguous fields from the optic disc margin and six macular contiguous fields one disc diameter below macular center. All nuclei without segmentation or degenerative changes in the ganglion cell layer were considered as ganglion cell nuclei in this study. We did not distinguish between ganglion cells and displaced amacrine cells. Average ganglion cell count/high power field was calculated in each area. Results: In the nasal area, the average ganglion cell counts per field were 32.5 (range; 27.8–36.3) in nondiabetic controls and 28.0 (range; 4.8–35.8) in diabetic monkeys (p = 0.26). In diabetic monkeys, the average counts were 31.6 (range; 25.5–35.8) in the retinas that did not show any histologically–determined diabetic retinal changes and 24.3 (range; 4.8–32.8) in retinas with retinopathy (capillary dropout) (p = 0.23). In the macular area, the average ganglion cell counts per field were 90.1 (range; 79.5–110.2) in nondiabetic control and 70.1 (range; 9.5–117.7) in diabetic monkeys (p = 0.20). In diabetic monkeys, the average counts were 91.0 (range; 71.5–117.7) in the retinas that did not show any retinal changes and 53.4 (range; 9.5–78.5) in retinas with retinopathy (p = 0.047). The count was lower in all areas counted in specimens with retinopathy, even where vascular insufficiency was not apparent. Conclusions: Ganglion cell numbers were reduced in diabetic animals with retinopathy, but not in hyperglycemic animals without retinopathy. The loss in ganglion cells was present throughout the retinas with retinopathy, not just in areas with angiopathy.

Keywords: diabetic retinopathy • ganglion cells