Functional damage to inner and outer retinal cells in experimental glaucoma.

Purpose: To investigate the cellular sources underlying the functional damage observed by multifocal electroretinography (mfERG) responses of glaucomatous eyes of monkeys.

Methods: First- and second-order (K1 and K2, respectively) mfERG responses of three normal and three experimentally induced glaucomatous eyes of cynomolgus monkeys were measured at two different levels of luminance. Retinal contributors to the responses were isolated by intravitreal injections of pharmacological agents that suppress specific retinal cells. gamma-Aminobutyric acid (GABA) and glycine were administered to block inner retinal function, followed by 2-amino-4-phosphonobutyric acid (APB), to block ON-bipolar cells.

Results: An inner retinal component removed by GABA and glycine was found in both the normal and glaucomatous eyes. However, it was attenuated in the latter, correlating with changes observed in the baseline K1 responses. Delays in the latency of outer retinal components were found in the responses of the glaucomatous eyes. K2 responses were dominated by an inner retinal contribution and were diminished in the responses of glaucomatous eyes. The outer retina responded to increased luminance with a shorter implicit time. A distinct wave part of the inner retinal component responded to increased luminance with increased amplitudes.

Conclusions: The integration of the retinal sources forming the mfERG response was compared between normal and glaucomatous monkey eyes. Both inner and outer retinal functions were aberrant in the responses of the glaucomatous eyes, with the attenuation of the inner retinal function more conspicuous. Nevertheless, glaucomatous eyes retained certain inner retinal activity, despite the advanced stage of disease. K2 responses were more sensitive to glaucomatous changes than were K1 responses.