Diagnosing functional visual deficits with the P300 component of the visual evoked potential
V. L. Towle, E. Sutcliffe and S. Sokol
The visual evoked potential (VEP) is routinely used to assess visual
function, though it occasionally does not reflect a patient's conscious
experience. Reports of normal flash or pattern VEPs obtained from blind
persons are extreme examples of this problem. The difficulty in
interpreting VEPs in light of such findings can be partly overcome by
obtaining a cognitive component of the evoked potential, P300. We obtained
traditional visual acuity measurements, pattern-reversal VEPs, and VEPs
containing P300s from three patients with clinically diagnosed functional
visual deficits. The P300s were obtained in response to stimuli that the
patients claimed they could not see, supporting the clinical conclusions
that malingering or hysteria was involved. The P300 component can be
helpful in assessing the subjective visual experience of patients suspected
of having functional visual loss.