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Purpose: Type 2 diabetes occurs spontaneously in rhesus monkeys and shows an extraordinary similarity to human diabetes in clinical features and relative time course. The purpose of this study was to investigate clinically and histopathologically the ocular changes in these monkeys., Methods: Ophthalmoscopic examinations were performed on aged normal and diabetic monkeys. Retinas from 16 diabetic monkeys and 6 nondiabetic monkeys were incubated postmortem for adenosine diphosphatase (ADPase) activity (labels viable retinal blood vessels) and flat-embedded in JB-4. Tissue sections were cut through areas of interest., Results: Cotton-wool spots, intraretinal hemorrhages, and hard exudates in the macula were observed by ophthalmoscopy in some diabetic monkeys. Dot/blot hemorrhages, cotton-wool spots, and small nonperfused areas were the earliest histologically documented changes in the retinas. Large nonperfused areas extending from optic disc to midfovea were observed in four diabetic monkeys. Formation of small intraretinal microvascular abnormalities (IRMAs) and microaneurysms were associated with the areas of nonperfusion. There were apparent fluid-filled spaces in the outer plexiform layer in three of these maculas, suggesting macular edema. There was a significant correlation between the occurrence of retinopathy and hypertension (P = 0.037 for systolic pressure; P = 0.019 for diastolic pressure). In elastase-digested retinas, the ratio of pericytes to endothelial cells was 0.66:1 in diabetic and 0.64:1 in nondiabetic (P = 0.75) retinas., Conclusions: This is the first detailed analysis of retinopathy in a colony of spontaneous type 2 diabetic monkeys. Monkeys with type 2 diabetes have many of the angiopathic changes associated with human diabetic retinopathy. Hypertension correlates with the severity of the diabetic retinopathy.

Purpose: An image-analysis technique was developed to quantify changes in the retinal pigment epithelium (RPE) and choriocapillaris in eyes of deceased donors with age-related macular degeneration (AMD)., Methods: Both eyes of two donors with AMD and of one normal control donor were used to develop this technique. After removal of the anterior segments, the eyecups were hemisected through the macula, with the disc included in one half of the eyecup. The choroid with RPE cells was dissected from the sclera and incubated for alkaline phosphatase (APase) activity, and the pigment was partially bleached with H2O2. The APase-incubated choroid was flat embedded and sectioned after image and morphometric analyses. Quantitative computer-assisted morphometric analyses of the two AMD-affected eyes (cases 1 and 2) were compared with analysis of the normal eye of a 70-year-old control subject (case 3)., Results: The right eye in case 1 had geographic atrophy (GA) and demonstrated a large area in the posterior pole with very few RPE cells (90% loss of RPE), but the border of the area of RPE atrophy was not well defined. The density of choroidal blood vessels in this area was reduced 30% to 50%, compared with the same regions in the control eye. No area was completely devoid of choriocapillaris. Clinically undetected choroidal neovascularization (CNV) was observed in the right eye in case 1 in both the periphery and the macula and was generally associated with surviving RPE cells. The right eye in case 2 had GA (areolar RPE atrophy) and demonstrated a reduction in vascular density in the area from disc to macula that was even greater than that in the eye in case 1 (53% reduction in the submacular region). RPE atrophy between the disc and macula was almost complete. The border of the RPE defect was clearly delineated and coincided closely with the area of decreased choroidal vascular density. Surviving choriocapillaris in the area of RPE atrophy was significantly narrower than choriocapillaris in the control subject and in normal areas of the eyes with GA (P < 0.0001)., Conclusions: In these eyes with GA, RPE atrophy was more severe than loss of choriocapillaris. Surviving choriocapillaris in areas with complete RPE loss was highly constricted. The association of surviving RPE cells with CNV suggests that RPE cells may furnish a stimulus for new vessel formation or stabilization.

Purpose: Pigment epithelium-derived factor (PEDF) is a protein produced by the retinal pigment epithelial (RPE) cells. Recent studies have implicated PEDF in activities that are inhibitory to angiogenesis. In this study, the expression of PEDF was investigated in normal rat eyes and in eyes with experimentally induced choroidal neovascularization and compared with the expression of vascular endothelial growth factor (VEGF)., Methods: Choroidal neovascularization was induced by laser photocoagulation in rat eyes. At intervals of up to 2 weeks after photocoagulation, the eyes were removed and prepared for in situ hybridization and immunohistochemical study. In situ hybridization was performed with digoxigenin-labeled PEDF riboprobes. Protein expression of PEDF and VEGF was studied immunohistochemically., Results: In normal adult rat eyes, PEDF mRNA was observed mainly in the corneal epithelial and endothelial cells, lens epithelial cells, ciliary epithelial cells, retinal ganglion cells, and the RPE cells. During the development of choroidal neovascularization, PEDF mRNA, PEDF protein, and VEGF protein were strongly detected in many cells within the laser lesions at 3 days after photocoagulation, after which levels gradually declined. However, PEDF was still expressed in the RPE cells that proliferated and covered the neovascular tissues at 2 weeks, whereas VEGF protein was weakly expressed in endothelial cells in choroidal neovascularization., Conclusions: PEDF is expressed in different cell types of normal rat eyes. The expression of PEDF was detected in the choroidal neovascular tissues induced by photocoagulation, and these findings suggest that PEDF may modulate the process of choroidal neovascularization.