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D Keating, S Parks, A Evans, DC Smith; The Multifocal ERG: Unmasked by Selective Cross-Correlation . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1792.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:To examine the construction of the first and second order multifocal ERG responses by recovering the response to specific pulse trains embedded in the m-sequence. Methods:A custom built p.c.based multifocal system driving a LED stimulator was used to record a 61 element multifocal ERG and a global ERG. The 61 area recording was compared to a standard CRT recording. The Global ERG recording was used to enable the recovery of different pulse trains embedded in the m-sequence. Summation of these individual pulse trains was performed and the results compared with the standard full cross-correlation. An isolated response was also recovered from the raw data and this response input into a simple superposition model to predict the waveform shape for specific pulse trains. The superposition model was compared with the actual selective cross correlation for a particular pulse train. Results:The 61 area multifocal ERG from the LED stimulator shows good agreement to the CRT recording. The summation of the selective cross correlation components gives identical responses to the full cross correlation. Although the general waveform shapes can be predicted from the superposition model, differences do exist as the model is linear and does not account for non-linear contributions. The selective cross-correlations are taken directly from the m-sequence and therefore do include the linear and non-linear components. Examination of the selective cross correlation data indicates that the P1 component is dominated by the same mechanisms generating the isolated response. The N1 component is dominated by the 0-0 and 1-1 pulse trains. The N2 component is the most complex component and includes an adaptive component due to interactions between consecutive stimuli and an inverted component originating from the P1 component one base period further on in time. Conclusion:: The multifocal ERG response is a complex composite response from a number of different pulse trains. Both the first and second order multifocal ERG waveforms are composite responses giving information on both linear and adaptation mechanisms present in the retina.
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