Protection of Ganglion Cells in Experimental Glaucoma by Retinal Laser Photocoagulation

Objective To test a hypothesis of photoreceptor involvement in retinal ganglion cell (RGC) death in chronic glaucoma. Methods Laser spots were applied to 6 eyes of 3 rhesus monkeys, causing focal destruction of the outer retina, including the photoreceptors. After 3 to 4 weeks, experimental glaucoma was induced in the right eyes of each monkey using argon laser trabecular destruction (ALTD). The intraocular pressures in these eyes were elevated for 3 to 7 months. As a control, 1 additional monkey underwent retinal laser photocoagulation followed by optic nerve transection instead of ALTD. Following enucleation, the retinas were embedded and sectioned for histologic evaluation. Results There was extensive loss of RGCs in the eyes with ALTD except over the large retinal laser spots, where there was an increased survival of RGCs. The RGC protection was not observed in the monkey that had undergone optic nerve transection. Conclusion Photocoagulation of the outer retina that completely destroys the photoreceptors results in survival of the overlying RGCs in experimental glaucoma in monkey eyes. Clinical Relevance Although this is an experimental model and not a therapeutic option, these results suggest that treatments other than lowering intraocular pressure may be potential therapies for preventing RGC death in glaucomatous eyes.