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M.K. Menz, M.D. Menz, E.E. Sutter; Lateral Interaction Effects on the Fast Adaptive Mechanisms Revealed With the Multifocal ERG . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3438.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To study how lateral interactions affect fast adapting responses of the normal human retina during a fast initial phase of light adaptation after a brief period of darkness. Methods: Multifocal electroretinograms (mfERG) were recorded from four normal subjects using a special stimulation mode (time–slice recording introduced at ARVO 2004, Poster #4228). A brief interval of darkness (133 ms or 10 video frames) was followed by a series of m–sequence modulated test frames (6 frames) probing the multifocal responses at intervals of 13.3 ms during the following 80 ms period of light adaptation. The intensity of the probe flashes was 2.7 cd*s/m^2, which resulted in a mean light adaptation level of 100 cd/m^2. The stimulus display consisted of 103 hexagons. To study the effects of lateral interactions, 68 hexagons were kept dark throughout, such that a ring of 6 masked hexagons surrounded each stimulated hexagon. The results were compared to the control experiments without masking. Results: In the experiment with the dark mask, the response amplitudes adapted rapidly to approximately 25% of the response to probe 1. Response waveform and peak implicit times changed very little between the 6 probe flashes. In the control experiment where all neighboring hexagons were stimulated adaptation in the center and the periphery followed a different time course. Near the center amplitudes had adapted to about 10% of the final level already after the first probe while the peripheral rings reach a minimum only with the fourth probe flash. Response waveforms exhibited larger changes in shape and implicit time as the retina adapts. The largest lateral effects were seen in the oscillatory potentials (OPs). The dark surround around the stimulated patches largely suppressed the OPs seen in the response to the first probe. In the center the OP suppression by the dark surround was complete but decreases toward the mid periphery until, in the outermost ring, OP amplitudes reached the same level as in the control experiment. In both experiments the oscillatory potentials are practically eliminated after the first probe flash at all eccentricities. Conclusions:The results suggest that the stimulation of neighboring retinal areas exerts a strong effect on the time course of local retinal adaptation. The response dynamics reflected in the response waveforms and particularly in the OPs are strongly affected by lateral interactions. These effects depend on retinal eccentricity.
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