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Y. Shimada, M.A. Bearse, E.E. Sutter; Multifocal Electroretinograms Combined with Periodic Flashes: a parametric study . Invest. Ophthalmol. Vis. Sci. 2004;45(13):4229.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To investigate the retinal responses generated by flash interactions in a recently introduced "global (full–screen) flash" stimulus paradigm of multifocal electroretinogram (mfERG). Methods: Five normal controls were studied with the stimulation combining multifocal (pseudorandom) flash with interleaved global (periodic, full–screen) flash. Two distinct response components were obtained: the mean response to the focal flashes (referred to as the direct response, DR) and the effect of the focal flash on the responses evoked by the global flash (the induced component, IC). Intensities of the two flashes were independently varied and the amplitudes and latencies of the components were measured. Results: Increasing the global flash luminance reduced DR amplitude and shortened DR implicit time. At the same time, a small hump on the rising slope of the peak of the DR disappeared. IC amplitude peaked with a moderate global flash (1.33 – 2.67 cds/m2). With a global flash of the right intensity, a weak focal flash could evoke a considerable IC even when the direct response was barely detectable. IC topography had a large naso–temporal asymmetry. Conclusions: While the DR is the average response generated by the local flashes regardless of the context of preceding and following flashes, the IC represents the difference in the global flash response in the presence and absence of the preceding focal flash. As the focal flash responses were always preceded by the periodically occurring global flashes, they reflect the resulting adapted or desensitized state of the retinal patch. The amplitude of the IC was largest in the presence of global flashes of moderate intensity. This pure, non–linear response component is thought to reflect predominantly inner retinal function.
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