Talc retinopathy in primates: a model of ischemic retinopathy. II. A histopathologic study.

Experiment talc retinopathy was produced in four adult rhesus monkeys by biweekly intravenous injections of talc for 31/2 to ten months and was studied by retinal vascular flat preparations and by light microscopy. Talc particles were lodged in the walls of the precapillary arterioles and capillaries, producing focal occlusion of retinal and choroidal capillaries. The pericyte-endothelial cell ratio was 1:0.77 in the posterior pole and 1:0.53 in the retinal periphery. The horseradish peroxidase study showed leakage of tracer from the retinal vasculature into the extracellular interstitial space, but the barrier of the retinal pigment epithelium was intact. Microinfarcts produced small cystoid spaces in the outer plexiform layer, inner nuclear layer, and ganglion cell layer of the macula. Cytoid bodies and macrophages were scattered in the retina. No retinal or vitreal neovascularization was observed.