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R. Windisch, A. F. Cruess, F. Tremblay; Modeling of the ON and OFF Interaction of the Photopic ERG Oscillatory Potentials. Part II: Similar OPs Response to Different Stimulus. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3803.
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To investigate the relationship between the generation of ON and OFF OPs in view of modeling their responses to various stimulus conditions.
Ten healthy adult subjects were investigated with nine electroretinogram (ERGs) protocols. General procedures included pupil dilatation, corneal anesthesia and use of a Lovac contact lens referenced to the forehead (ground at the earlobe). OPs were averaged 20 times after analog filtration with a 100 Hz high pass filter. Each protocol was a combination of three flash intensities (3.2, 5.6 and 10.1 cd•s/m2) and three background intensities (6.8, 34 and 68 cd/m2). For each protocol, neutral density (ND) filters ranging between 0-1.05 log units (0.15 increment) were interposed, thus changing the intensity of the stimulus conditions but not the difference between the flash and background intensities, herein referred as "contrast". All data was exported to a spreadsheet to be analyzed by ANOVA with repeated measures in terms of amplitude and implicit time
OP2 and OP4, taken as representative OPs for the ON and OFF responses, showed, as expected from a previous study,1 absolute amplitude and implicit time that decreased as the intensity of the flash/background combination decreased over the 1.05 log attenuation created by interposition of the ND filters. Interestingly, we found that the difference of implicit time between the ON and OFF templates remained constant for each of the nine combinations of flash/ background intensities when ND filters were interposed. This occurs independently of the absolute values taken by the flash/background combination as long as the difference in intensity between the two remained constant.
The ON and OFF OPs maintain a constant temporal relationship in conditions of constant "contrast" between the flash and the background intensities. The overall configuration of the photopic response, with its independent ON and OFF components, can thus be predicted based not on the absolute values of the stimulus conditions but rather with the "contrast" between the flash and the background intensity.1. Windisch et al., IOVS 2007;48:ARVO E-Abstract 536
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