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Kate Godwin, Paul DeMarco; Change in Flash Electroretinogram Morphology from Scotopic to Photopic Conditions. Invest. Ophthalmol. Vis. Sci. 2013;54(15):6120.
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We examined the change in morphology of the human long-flash electroretinogram (ERG) as retinal adaptation progressed from scotopic to photopic levels.
Data were collected from human subjects using increment and decrement flashes and standard ERG recording techniques. Subjects first dark-adapted for thirty minutes, and were then presented with increment and decrement flashes at several background levels ranging from -2.25 to 2.29 log cd/m2, so as to capture the transition from rod-dominated to cone-dominated vision. Each flash was presented for 250 ms, with a 2 s interstimulus interval. Both the time time to peak and amplitude of waveform components were assessed at each background level.
At the lowest background levels, the ERG consisted of a rod b-wave in response to increment flashes. As retinal adaptation progressed through the mesopic to photopic ranges, a small a-wave appeared, and the b-wave time to peak decreased. For decrement flashes, the ERG was negative at scotopic levels, but at higher mesopic levels a small positive hump was present, which morphed into a frank d-wave as adaptation levels entered the photopic range.
As the retina progressed from a scotopic to a photopic state, evidence of cone contribution to the ERG became more apparent. In particular, the d-wave, which is a signature of hyperpolarizing bipolar cells and passage of photoreceptor signals through cone pathways, was absent at scotopic levels. These data are consistent with the ERG being shaped by the rod photoreceptor to rod-bipolar cell pathway at scotopic levels. As adaptation transitions to the mesopic state, signatures of the cone ON- and OFF-pathways emerge, shaping the b-wave into a more transient response and causing the evolution of the d-wave.
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