Amplitude Decrease of Photopic ERG b-Wave at Higher Stimulus Intensities in Humans

Abstract

Purpose: The b-wave of the human photopic electroretinogram (ERG) elicited by a short-flash increases in amplitude with increasing stimulus intensities at lower stimulus levels, but then decreases at higher stimulus intensities. The purpose of the present study was to explore this phenomenon in more detail, using short- and long-flash stimuli. Methods: The intensity-response functions of the b-wave elicited by short- and long-flashes were compared from threshold to higher stimulus intensities in 5 normal subjects. Short- and long-flash ERGs were elicited under rod-saturating background levels using white light-emitting diodes built into a contact lens electrode. Results: Whereas the amplitude of the short-flash b-wave decreased at higher intensities, the amplitude of the long-flash ERG b-wave did not decrease but plateaued. The long-flash ERG d-wave or OFF-response decreased at higher stimulus levels as did the short-flash elicited b-wave. Conclusions: Because it is widely accepted that the b-wave and the OFF-response d-wave interact to produce a single positive response, our results suggest that the decrease in the b-wave amplitude at high stimulus intensity is caused by the decrease of the d-wave at the higher stimulus intensities.