Retinal and Choriocapillaris Thickness Changes in Spontaneously Diabetic Macaques

Beyond the clinically apparent damage to the retinal vasculature, diabetes affects the neuroretina and choroid. Nonhuman primates (NHPs) serve as valuable models for human retinal diseases, including diabetic retinopathy. This study aimed to investigate changes in the thickness of the retina, RPE, and choriocapillaris in spontaneously diabetic cynomolgus macaques.

Optical coherence tomography (OCT) images were obtained from 25 diabetic macaques and 26 age-matched nondiabetic macaques. The thickness of individual retinal layers in the macula, along with RPE and choriocapillaris, was measured manually. Choriocapillaris thickness was assessed in postmortem human globes from diabetic and nondiabetic individuals.

Diabetes predominantly affected the inner retina more than the outer retina in macaques. Notably, the nasal retina showed greater thinning compared to the temporal retina. A slight but significant thickening of the inner nuclear layer was observed. No changes were detected in the thickness of RPE/Bruch's membrane complex via OCT. However, a significant increase in choriocapillaris thickness was noted in the diabetic macaques. Postmortem human specimens from patients with nonproliferative diabetic retinopathy (NPDR) also demonstrated thickening of choriocapillaris/Bruch's membrane.

Consistent with humans, early diabetes in cynomolgus macaques results in notable alterations in retinal thickness, particularly affecting the nasal inner retina. The observed increase in choriocapillaris thickness in both diabetic macaques and human patients with NPDR likely indicates pathologic changes and remodeling due to diabetes. Cynomolgus macaque presents a valuable NHP model for studying diabetic retinopathy.