Study of retinal microvessels in a Rhesus monkey model of chronic high intraocular pressure

To investigate the changes in retinal vessels, especially macular capillaries, under high IOP using the Rhesus monkey high IOP model.

The trabecular meshwork of the adult Rhesus monkey was cauterized by laser to induce increased IOPs with different degrees of damage. The eyeballs were enucleated, and the optic nerves were stained with toluidine blue in semithick slices. Part of the retina was observed under electron microscope, and the rest was stained by the ADPase method. The damage levels of the optic nerve were evaluated by axon count, and the pathological appearance of the macular capillaries were observed.

Five mildly damaged eyes, three moderately damaged eyes and three severely damaged eyes were evaluated. Dense and intact perifoveal vascular rings were observed in all the eyes. The vessels' area percentages, as well as area, perimeter and diameter of the foveal avascular zones, were measured, and no statistically differences were found among different groups (P-values were 0.269, 0.500, 0.951, and 0.555 separately). The ultra structures of the normal capillaries showed regular tubes and intact basement membranes, while lipoid substances in capillary tubes, swollen mitochondria in endothelial cell bodies, and uneven basement membranes were found in the high IOP-damaged eyes.

Compared with normal eyes, no obvious differences were found in macular microvessels and foveal avascular zones in the Rhesus monkey model of high IOP. However, presence of swollen mitochondria in endothelial cells and lipoid substances in capillary tubes might suggest that high IOP could damage the capillary endothelial cells.