Choroidopathy in the Spontaneously–Diabetic Monkey

Abstract

Abstract: : Purpose: Although the choroidal vasculature accounts for 80% of the circulation in the eye and supplies 90% of the oxygen to outer retina in the dark, the contribution of choroidopathy to function loss in disorders such as diabetes that have significant vascular components is often ignored. This is because the choroidal circulation is difficult to visualize under typical clinical conditions, and its anatomy is complex and shows large individual differences. The finding of significant choriocapillaris dropout in human cadavers who had diabetes (Cao J., McLeod S., Merges, C.A., Lutty, G.A. Arch. Ophthalmol. 116: 589–597,1998)., however, suggests that choroidal circulation needs to be better evaluated as a source of vision loss in diabetes. Methods:We evaluated choroidal circulation in a colony of rhesus monkeys that spontaneously developed type 2 diabetes, using fluorescein and indocyanin green (ICG) video angiography. Age–similar normoglycemic monkeys were studied for comparison. Velocity of blood flow in the retrobulbar arteries was measured using duplex color Doppler ultrasound. Multifocal electroretinograms documented visual function loss. Immunohistochemistry was performed on eyes of animals that had been electively euthanized due to failing health. Results: Thirteen out of 13 monkeys with diabetes, and 3 out of 7 normal monkeys had areas of choriocapillaris nonperfusion (p = 0.0005, Fisher’s exact test). Of these 3 normal monkeys, 2 were hypertensive and one had advanced cardiomyopathy. Peripapillary choriocapillaris nonperfusion was the most consistent abnormality, and was much more pronounced in the diabetic monkeys than in the 3 normal monkeys. Two of the diabetic monkeys also had reduced blood flow velocity in the ophthalmic artery. Hypertensive changes such as basement membrane duplication were readily observed in choroidal arterioles. Visual function loss evaluated by the multifocal electroretinogram directly correlated with loss in viable choriocapillaris. Conclusions: : Choriodal perfusion abnormalities are consistent features of ocular disease in spontaneously diabetic monkeys.

Keywords: diabetic retinopathy • choroid • electroretinography: clinical