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T. Meigen, R. Pohl; Reliability of Pattern Onset VEPs Can Be Improved by Synthesizing Full-Field Responses From Pattern-Pulse Multifocal Recordings. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5876.
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© ARVO (1962-2015); The Authors (2016-present)
Cortical electrophysiological signals from different parts of the visual field may be annihilated by destructive interference. The aim of this study was to test whether the signal strength and the latency reliability of full-field pattern onset VEPs can be improved by rectifying multifocal visual evoked potentials (mfVEP).
20 visually normal subjects participated in the study. MfVEPs from the right eye were recorded with an Oz-Fpz derivation and a bipolar derivation between two electrodes placed 4 cm above and below the inion. A dartboard pattern with a diameter of 38º was subdivided into 6 wedge-shaped stimulus fields. Within each field checkerboard patterns with eccentrically scaled check size, a mean luminance of 50 cd/m2 and a contrast of 99% were presented with a pattern pulse stimulation mode, similar to James (2003). The average temporal frequency was 2.0 Hz. MfVEP traces were derived by multiple regression. By summation of the 6 mfVEP traces with different signs two synthesized full-field VEPs were calculated that boosted either (A) the early C1 and C2 components, or (B) the late C3 component of the pattern onset VEP. Amplitude and latency differences between A or B and a full-field stimulation of all 6 fields (C) were tested for significance with a paired t-test.
(1) The synthesized waveforms A and B showed a massive increase in amplitude (Table) when compared to the full-field recording C. (2) The amplitude gain ranged from a factor of 1.68 (C3, Oz-Fpz, p=0.00025) to 6.61 (C1, bipolar derivation, p<10-8). (3) As A, B, and C showed different waveforms, a direct comparison of latency results was less reasonable. However, major components of A or B showed a significantly lower latency variability than components of C in similar time intervals.
The data suggest that the inter-individual variability of standard full-field pattern onset VEPs may be due to the annihilation of large and less variable VEP signals from different parts of the visual field. As rectifying these signals led to a dramatic increase in amplitude and to a decrease in variability the multifocal technique may help to detect visual dysfunction better than with standard full-field recordings.
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