Comparative Study Of Three Methods Of Experimental Rat Glaucoma: Distribution Of Surviving Retinal Ganglion Cells

Abstract

Abstract: : Purpose:To compare three different experimental models of rat glaucoma in terms of increased intraocular pressure (IOP) and damage to retinal ganglion cells (RGCs) by means of morphometric analysis. Methods:Increased intraocular pressure was induced by three different methods: 1) cauterization of three episcleral veins, 2) several injections of latex fluorospheres in the anterior chamber and 3) several injections of methylcellulose and latex fluorospheres in the anterior chamber. Measurement of IOP was performed weekly by using a Tonopen XL. After 6 months, RGCs were retrogradely labeled with fluorogold and dextranamine, both applied in the optic nerve. Retinas were processed and visualized with a fluorescent microscope, and images were acquired using a digital camera. RGCs were counted and measured in order to characterize the pattern of RGC death induced by the damage. Results:A similar increase in IOP was observed in the three glaucoma models which we employed, with an IOP reaching values of 31.4 mm Hg in the treated eye. This increase was monitored for the duration of the entire experimental period. The mean percentage of RGCs that die after the damage was estimated as 17%, 24% and 15% in fluorospheres, fluorospheres+methylcellulose and episcleral group, respectively. RGC death was not found to be homogeneously distributed throughout the retina. Thus, in the peripheral region a higher level of RGC death was found in retinas after the cauterization of episcleral veins. Finally, we observed that the injections of fluorospheres or fluorospheres plus methylcellulose into the rat eye caused substantial peripheral corneal neovascularization. Conclusions:A similar increase in IOP was observed with the three experimental models of glaucoma which we studied. Moreover, differences in the extent of RGC death associated with the three methods were not observed. However, since cauterization of the episcleral veins is a less invasive method, this seems to be the best model of experimental glaucoma in rat.

Keywords: cell death/apoptosis • intraocular pressure • retina: proximal (bipolar, amacrine, and ganglion cells)