Heine M., Meigen T.

Universitäts-Augenklinik Würzburg, Josef-Schneider-Str. 11, 97080 Würzburg

Introduction: Visual evoked potentials (VEPs) can be used to assess visual acuity. To identify the most sensitive recording condition for VEPs recording near threshold we evaluated the statistical significance of steadystate VEP responses recorded with different electrode positions.
Methods: In 10 emmetrope volunteers (24-60yr) we recorded VEPs monocularly with a 4-channel derivation (Oz referenced to an array of four occipitally placed electrodes surrounding Oz). Checkerboard patterns were presented with 8 check sizes (0.69¡-10.71¡), a contrast of 99%, a mean luminance of 50 cd/m2, within a stimulus field of 15¡x11.3¡. The steadystate- stimuli (16 rps) were presented in a pattern onset/offset mode(15ms/45ms). We derived the statistical significance of the VEP responses by comparing the Fourier component at the stimulus frequency to the average magnitude of the two neighboring frequencies. We investigated the portion of statistically significant VEP responses (p<1%) according to the criteria: a) VEP responses of the single channels are significant b) the averaged VEP responses across all channels are significant (Laplacian derivation) c) at least one VEP response of all utilized single-channels was significant (rcorrected for multiple testing).
Results: The portion of statistically significant VEP responses was as follows: a) 79%, b) 76.25% und c) 91.2%.
Conclusions: The averaging of VEP-waves as performed in Laplacian derivation (b) does not enhance the signal-to-noise-ratio compared to the analysis of the single channels (a). However, multichannel recording and analysis with different electrodes (c) may still be reasonable for the most significant VEP-response is not always derived at the same electrode position.

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