Experimental model of ocular hypertension in the rat: study of the optic nerve capillaries and action of hypotensive drugs.

PURPOSE To investigate quantitatively the effect of elevated intraocular pressure (IOP) on the microvasculature of the optic nerve with and without topical treatment with two hypotensive drugs, timolol and latanoprost. METHODS Three groups of rats underwent cauterization of three episcleral veins to produce elevated IOP in the right eye. Two of these groups were treated with timolol or latanoprost for 3 months. Eyeballs were incubated with anti-GLUT-1 polyclonal antibody. GLUT-1-positive capillaries of the optic nerve head (ONH) and optic nerve exit (ON) were examined and analyzed for their number per square millimeter, volume fraction, length per unit volume, surface area per unit volume, and mean diameter. RESULTS An increase in IOP resulted in a significant decrease in microvessel density in the laminar region (LR) and postlaminar region (PR) and ON compared with the control group. The other parameters fell significantly in all regions of the optic nerve. Topical treatment with timolol or latanoprost did not modify the density of the capillaries, although the other parameters increased significantly compared with the untreated experimental group. Additionally, the mean diameter of the capillaries in the LR and the PR recovered after treatment. CONCLUSIONS The results indicate that the capillaries of the LR and the PR of the ONH are the most susceptible to IOP elevation. The authors suggest that timolol and latanoprost have a certain vascular action by increasing the available blood volume, surface area per unit volume, length per unit volume, and diameter of the capillaries of the ONH in these two regions.