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E. V. Vukmanic, P. J. DeMarco; Parametric Analysis of the Human ERG to Long Duration Stimuli. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1499.
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© ARVO (1962-2015); The Authors (2016-present)
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.
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.
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.
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.
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