Chloroquine retinopathy in the rhesus monkey.

Chloroquine was administered intramuscularly 5 days a week to rhesus monkeys for as long as 4 1/2 years. No clinical, fluorescein angiographic, or electrophysiological evidence of retinal damage was observed. Yet chloroquine/chloroquine byproduct analysis of the ocular tissues revealed an enormous binding capacity of the pigmented tissues of the eye (choroid plus RPE, ciliary body, and iris) with eventual accumulation observed in the retina. Despite the normal ophthalmic appearance and function, extensive pathological changes occurred in the retinas and choroids of these experimental monkeys. The chloroquine caused an initial dramatic effect on the ganglion cells, with the photoreceptors affected shortly thereafter. Patching degeneration of the ganglion cells and photoreceptors then progressed over several years, with the choroid and pigment epithelium ultimately deteriorating as well.