Critical flicker frequencies in MS patients with normal or abnormal pattern VEP.

Critical flicker frequencies (CFF) were compared with the latencies of visual pattern reversal evoked potentials (VEP) in 2 groups of MS patients to evaluate the value of CFF in electrophysiological diagnostics of demyelination of the optic tract. A microprocessor-based device was constructed to obtain CFF thresholds with a 2-alternative forced-choice method. VEP latency was more frequently pathological than CFF, but CFF was abnormal in 2 optic neuritis patients with normal VEP. The frequency of pathological CFF and VEP was different in the patient group with a long history of MS compared with the new cases; in the freshly diagnosed group, CFF had a better diagnostic yield compared to the patients with a longer history.