Purchase this article with an account.
JA Chisholm, S Parks, D Keating, AL Evans; A Multi-channel Multifocal VECP System . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4741.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Purpose:Multifocal visual evoked cortical potentials (mVECP) studies have shown that a wide range of waveforms are obtained from different individuals due to differences in cortical anatomy, making classification of a normal response problematic. Optimising electrode placement is one approach to reducing this variation between individuals and achieving high S/N responses to stimulation of all areas of the visual field. Indeed, several studies have investigated the placement of electrodes using a small number of recording channels and it has been recognised that improved mVECP recordings can be made when more than one channel is used. Methods: A custom multichannel mVECP has been created. The recording system utilises 48 active electrodes with sintered Ag/AgCl tips providing low noise, low DC offset and stable DC performance without the need for skin preparation. Reproducible electrode placement is made possible by the use of an EEG cap. The stimulus is a dartboard pattern containing 60 4x4 checkerboard patterns scaled for cortical magnification and is presented using a back-projection technique. A maximum length binary m-sequence is chosen that when decimated ensures orthogonality not only between elements but also between higher order elements to degree three. Cross-correlation of the recorded signals is performed off-line. Results: Multichannel recordings of physiological signals have successfully been recovered from our 48 active electrode system. Early investigations indicate that stimulation of a single part of the visual field results in responses of varying amplitude recorded by different electrodes. Furthermore, different recording channels recover the largest amplitude signal in response to different areas of the visual field. Conclusion: Multichannel mVECP recording improves the probability of recording optimal waveforms in response to stimulation of all areas of the visual field. This additional information will allow the selection of a small number of electrode positions that can conveniently be used clinically. It is hoped that selection in this manner will enable a reduction in the wide normal range which is inherent to the mVECP. Such an advance will greatly assist the introduction of the mVECP as a robust, objective assessment of the visual field.  Graham et al ARVO 358 2001
This PDF is available to Subscribers Only