Characterization of retinal injury using ERG measures obtained with both conventional and multifocal methods in chronic ocular hypertensive primates

PURPOSE. TO characterize, using both conventional and multifocal electroret inogram (ERG) recordings as well as histologic measures, retinal injury in the chronic ocular hypertensive primate model for experimental glaucoma. METHODS. Ocular hypertension was induced in the night eye of 7 cynomolgous monkeys, Macaca fascicularis, using laser injury to the aqueous outflow tis sue at the anterior chamber angle. At 16 months after IOP elevation, ERG re cordings were made from both eyes of all animals using both conventional an d multifocal methods. After electrophysiological recording, animals were ki lled and retinal samples were radially sectioned for histologic analysis. RESULTS. Histologic measures showed that ocular hypertensive injury was lar gely or completely limited to a loss of retinal ganglion cells (RGCs). The degree of RGC loss was similar in central and peripheral retina. Amplitudes of conventional ERG responses were mostly unaffected in eyes having severe loss of RGCs, a finding that is consistent with limited injury to photorec eptors, bipolar cells, and amacrine cells. Peaks in both the first- and sec ond-order multifocal ERG responses were attenuated in ocular hypertensive e yes, and amplitude of these peaks was highly correlated with the density of surviving RGCs. CONCLUSIONS. The results are consistent with a conclusion that both first- and second-order components of the multifocal ERG response from the monkey reflect a significant contribution from activity in RGCs and may provide a useful measure for the clinical diagnosis and management of glaucoma.