Spectral characteristics of the PhNR in the full-field flash electroretinogram of normals and glaucoma patients.

Flash electroretinogram responses were measured in normal subjects to different chromatic combinations of flashes and backgrounds. The amplitudes of the flash response components were measured at different flash strengths and could be described by a generalized Naka-Rushton function. The measurements were repeated at different background luminances to study adaptation effects. It was found that when flash strength and background luminance were expressed in photometric terms (cd s/m² and cd/m², respectively), then the responses were very similar for all chromatic combinations with the exception of the condition in which blue (peak wavelength 458 nm) was flashed upon an orange (peak wavelength 591 nm) background. We propose that in this condition, a second (possibly S-cone or rod-driven) mechanism intrudes. The negative response after the b-wave (here called "photopic negative response" or PhNR for all conditions) is thought to reflect ganglion cell activity and was also largest at this condition. Responses were measured to the 458 nm flash on 591 nm background and the reversed combination in a population of 39 normal subjects and 49 glaucoma patients. It was found that the PhNR amplitude was affected by glaucoma in all conditions. Other component parameters, reflecting responses and adaptation dynamics, were not altered. The best stimulus condition among the conditions used to separate the PhNR amplitude of normals and patients was a 1 cd s/m² 458 nm flash on a 10 cd/m² 591 nm background.