Abstract
Purpose: :
The flash electroretinogram (ERG) is a retinal evoked potential which reflects contributions from photoreceptors, bipolar cells, and inner-retina networks. The standard stimulus for the ERG is a short duration increment flash, but the morphology of the ERG waveform can be significantly influenced by the duration and polarity of the stimulus. Here we investigate the influence of long-duration positive and negative light stimuli on the morphology, amplitude and latency of the constituent ERG component waveforms.
Methods: :
ERG responses were recorded from human subjects using DTL fiber electrodes using standard recording procedures. Stimuli were positive and negative square-wave flashes, and rapid-on and rapid-off sawtooth stimuli, produced by a ganzfeld stimulator. Stimulation was initiated from a standard background luminance of 175 cd/m2. For square wave stimuli, flash duration was varied from 5-250 ms while flash contrast was varied +/- 85%. Mean intensity-response functions were derived for the b-wave and d-wave responses and fit with log-linear curves. Sawtooth stimuli were modulated at 4 Hz from the same mean luminance.
Results: :
Flash duration and polarity affects the morphological characteristics of both the b- and d-waves of the ERG. Analysis of the intensity-response functions for these waveforms reveals a steeper slope and larger amplitude for the d-wave response compared to the b-wave response to equal contrast flashes. The initial rise of the d-wave is consistent in time-course and slope to that of the a-wave, suggesting contribution from photoreceptors. Sawtooth stimuli produce ERGs that differ in morphology than ERGs induced by similar duration square-wave stimuli. Fourier analysis reveals distinct temporal frequency components in the ERGs to opposite polarity stimuli.
Conclusions: :
Intensity-response and duration-response measurement of the ERG reveal nonlinear summation of activity from ON- and OFF-retinal pathways. The use of opposite polarity stimuli expands the utility of the ERG as an analysis tool for the assessing the function, and integrity, of inner-retinal networks.
Keywords: electroretinography: non-clinical • electrophysiology: non-clinical