Visual evoked potentials standard (2004)

This document presents the current (2004) standard for the visual evoked potential (VEP). The VEP is an evoked electrophysiological potential that can be extracted, using signal averaging, from the electroencephalographic activity recorded at the scalp. The VEP can provide important diagnostic information regarding the functional integrity of the visual system. The current standard presents basic responses elicited by three commonly used stimulus conditions using a single, midline recording channel with an occipital, active electrode. Because chiasmal and retrochiasmal diseases may be missed using a single channel, three channels using the midline and two lateral active electrodes are suggested when one goes beyond the standard and tests patients for chiasmal and retrochiasmal dysfunction. Pattern reversal is the preferred technique for most clinical purposes. The results of pattern reversal stimuli are less variable in waveform and timing than the results elicited by other stimuli. The pattern onset/offset technique can be useful in the detection of malingering and in patients with nystagmus, and the flash VEP is particularly useful when optical factors or poor cooperation make the use of pattern stimulation inappropriate. The intent of this standard is that at least one of these techniques should be included in every clinical VEP recording session so that all laboratories will have a common core of information that can be shared or compared.