Assessment of receptoral and post-receptoral changes in primary open-angle glaucoma

Purpose. There is conflicting evidence concerning the existence of receptoral involvement in POAG.^1,2 The purpose of this study was to determine the extent of rod and cone receptoral and post-receptoral dysfunction in patients with primary open-angle glaucoma (POAG). Methods. Full-field rod- and cone-mediated ERGs were obtained as a function of flash intensity from patients with POAG and from age-similar control subjects. The a-wave data were fitted with a computational model which yields the parameters R_max (the maximum response) and log S (sensitivity).^3,4 Cone oscillatory potentials (OPs) and 30 Hz flicker responses were also measured. In addition, two-color dark-adapted psychophysical thresholds (500 vs. 650 nm) and light-adapted L/M cone thresholds were obtained along the horizontal meridian. Results. Both rod and cone thresholds were increased for retinal areas with visual field deficits. Analyses of the rod and cone a-wave data showed that R_max values were normal, as were rod-mediated log S values. In 50% of the patients, cone-mediated log S values were decreased and cone OP implicit times were delayed. These delays were greater than predicted based upon the log S changes. Conclusions. Our results indicate mild deficits in cone receptoral function and additional deficits in postreceptoral function in POAG.