Protection of Retinal Function by a Novel Topical Formulation of Brimonidine in Laser–Induced Chronic Ocular Hypertensive Model in Rats

Abstract

Abstract: : Purpose: Brimonidine has been shown to be protective to ganglion cells in chronically elevated intraocular pressure (IOP). We have also shown that increase in IOP reduced retinal function measured by electroretinography (IOVS, 44, 2003). In this study we investigated whether a novel topical formulation of brimonidine (Alphagan–P) preserves retinal function as well. Methods: IOP was elevated by laser photocoagulation of episcleral and limbal veins. Alphagan–P treatment (5 µl twice a day) was started after first laser treatment and continued for two months. Electrophysiological recordings were done at light intensities of –20 and –4 dB’s two months after elevation of IOP using LKC ganzfeld stimulator. The oscillatory potential (OP) responses were extracted using analog by pass from the flash ERG. Results: Laser photocoagulation of the episcleral and limbal veins resulted in elevation of IOP from 15to 32 mm Hg in vehicle treated rats. However in rats that were treated maximum IOP obtained was 27 mm Hg. IOP elevation resulted in reduction of a–and b–wave and oscillatory potentials (OP). The OP was reduced to 31% of control. Treatment with Alphagan–P preserved the OP response to 74% of control. The latencies and amplitudes of a–and b–wave were also preserved by Alphagan–P. Conclusions: Treatment with Alphagan–P not only prevents elevated IOP–induced ganglion cell loss but also preserves retinal function.

Keywords: electroretinography: non-clinical • retina • neuroprotection