The choroid of primates possesses an elaborate nitrergic nerve fiber plexus containing a great number of ganglion cells. Postganglionic nerve fibers innervate mainly the choroidal vasculature. In addition, the choroid contains an elastic muscular system closely associated to the vasculature. The goal of the present investigation was to analyze how sustained IOP elevation would affect the choroidal vasculature with its specialized innervation and the adjacent retina. For this purpose the posterior eye segment of 15 rhesus monkeys which after laser coagulation of the trabecular meshwork developed elevated IOP up to 4 years were studied using immunohistochemical and histochemical methods, and scanning electron microscopy of corrosion casts. The most striking finding was a significant reduction of choroidal thickness and loss of choroidal ganglion cells and nerve fibers, especially in the central portion of the choroid. Corrosion casts of the choroidal vasculature showed a slight decrease in capillary density and a decrease in length of the arterioles in glaucomatous eyes. Whole mount preparations of the retina stained for NADPH diaphorase revealed a significant reduction in positively stained amacrine cells, reduction in diameter of arterioles and changes in the staining pattern of the retinal vasculature, particularly in the perimacular region.