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Richa Verma, Michael J. Pianta; Contribution of human cone photoreceptors to the photopic 30-Hz flicker electroretinogram. Journal of Vision 2006;6(13):9. doi: 10.1167/6.13.9.
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© ARVO (1962-2015); The Authors (2016-present)
For the photopic flicker electroretinogram (ERG) in monkey, pharmacological blocking of post-receptoral responses eliminates a large component of the flicker response 1,2. We have used a non-invasive approach to determine the cone contribution to the photopic ERG in humans using the paired-flash technique3.
ERG responses were recorded from three subjects with normal vision. Stimuli were presented in a Ganzfeld bowl with a steady rod saturating background. The test stimulus was 30Hz square wave flicker. At fixed intervals during a cycle (every 3ms), an intense probe flash was presented to rapidly saturate the cones. We assumed that at 4ms after the probe the dark current in the cones had been shut down while the post-receptoral response was unchanged. We take this probe response to be proportional to the magnitude of the cone current flowing at that time, and we derive the fractional probe response by normalizing to the probe-alone response.
We determined the fourier coefficients for the fundamental. The cone response amplitude formed a similar proportion of the overall flicker response amplitude for two subjects (8 & 6%), but was considerably higher for a third (56%). The cone response phase was similar for the same two subjects (78 % 70°), and was different for the third (275°), while the overall flicker phase was similar for all subjects (306, 300, and 317°).
These results indicate that the photoreceptor response is a small component of the photopic flicker ERG, with some individual variability in the relative contribution of the cone response.
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