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N. Mysore, P. Lachapelle; Let's Build an ERG: A Synthetic Approach to the Genesis of the Human Photopic Electroretinogram. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5810. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Schematically, the human photopic flash electroretinogram (ERG) can be portrayed as the addition of three major components: the slower frequency a- and b-waves, and the higher frequency oscillatory potentials (OPs). For more than half a century, it has been claimed that the OPs and b-wave are separately generated, the corneal ERG representing the sum of the two processes. We propose a different view where, through appropriate filtering and integration, the OPs can generate normal as well as pathological b-waves.
Analysis was performed on normal photopic ERGs [flash intensities: -0.8 to 2.84 log cd.sec.m2 in 14 steps; background: 30 cd.m2; broadband recordings: 1-1000 Hz; sampling interval: 0.293 ms] and selected pathological ERGs, where the OPs appeared to be more attenuated than the b-wave. Data was analyzed using Matlab 6.1 and the reconstructed (filtered and integrated) signals were compared to the original ERGs using a Pearson correlation coefficient. A butterworth filter was used and parameters were chosen to optimize the correlation coefficient: 3 dB bandwidth of 60 Hz to 250 Hz; a passband and stopband ripple of 1 dB and 5.5 dB, respectively.
Irrespective of the intensity used, the b-waves were always faithfully reproduced and the average Pearson correlation coefficient were > 89 % in normal and pathological responses. The reconstructed waveforms were minimally delayed (1-2 ms on average) and showed a maximum of a 10 microvolts amplitude bias. Finally, even when the OPs could not be evidenced in the broadband ERG, they could still be isolated from the filtering operation and the resulting integration matched the original b-wave.
Our results show that the OPs can be integrated to derive the b-wave in normal and pathological recordings. Furthermore, a linear relationship exists between the OPs and the b-wave amplitudes in all considered scenarios. Thus, our study provides an alternative to the belief that the OPs are superimposed on the b-wave, namely that the integration of the OPs would be involved in b-wave genesis. Supported by CIHR and Réseau Vision.
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