A-19. Visual evoked potentials: Basic technology and clinical applications

Abstract

Visual information is processed simultaneously via multiple parallel channels and each channel constitutes a set of sequential processes. The visual evoked potentials (VEPs) are the evoked electrophysiological potential that can be extracted, using signal averaging, from the electroencephalographic activity recorded at the scalp. VEPs can provide important diagnostic information regarding the functional integrity of the visual pathways and the visual cortex. Commonly used visual stimuli are flashing lights or pattern reversal (checkerboards or gratings) on the TV monitor or video screen. Pattern reversal is the preferred technique for most clinical purposes. The results of pattern reversal stimuli are less variable in the waveform and the 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. In addition, pattern reversal VEP to full-field stimulation is best suited to evaluate anterior visual pathways while hemi-field VEP is most effective in the assessment of chiasmal and post-chiasmal functions. This article presents the basic technology and current standard for flash and pattern reversal VEP recording methods based on the major parallel pathways of the visual system from the retina to the primary visual cortex via lateral geniculate nucleus that receive visual input.