Electrophysiological and histological measures of retinal injury in chronic ocular hypertensive monkeys

This study was performed to determine whether components of the standard ERG (electroretinogram), multifocal ERG, and flash VECP (visually-evoked cortical potential) response might provide a sensitive measure of retinal ganglion cell injury in a monkey model for chronic ocular hypertension.

Argon laser treatment of the aqueous outflow tissue was used to induce chronic elevation of intraocular pressure (IOP) in the right eye of 18 young adult cynomolgous monkeys. At 15 months post- IOP elevation, standard methods were used to record ERG and VECP responses. Multifocal ERG responses were also recorded at this time. Loss of retinal ganglion cells due to ocular hypertensive injury was determined by histological analysis of all retinas.

Ocular hypertensive retinal injury was associated with a loss of retinal ganglion cells. There was no histological or electrophysiological evidence for injury to any other retinal cell type. Correlation of electrophysiological response amplitudes with histological measures of retinal ganglion cell loss/survival yielded results which suggest that activity in retinal ganglion cells makes a substantial contribution to components of the 30 Hz flicker ERG, the flash VECP, and both first and second order multifocal ERG responses. Of the electrophysiological measures used in this study, multifocal ERG response amplitude had the greatest sensitivity to retinal ganglion cell loss.

Components of the multifocal ERG provide a sensitive measure of ganglion cell injury in a monkey model of chronic ocular hypertension. These same measures may have utility in the clinical diagnosis and management of glaucoma.