The visual-evoked potential in tobacco-alcohol and nutritional amblyopia.

Twelve subjects, nine with tobacco-alcohol amblyopia and three with nutritional amblyopia, were studied with pattern and flash visual-evoked potentials. We found abnormal steady-state responses in all 12 patients, including those with minor visual abnormalities, when the contrast of the stimulus was decreased. The latency of the first major positive wave (P100) of the flash- or pattern-evoked potential was not delayed in 11 of the 12 patients. The normal P100 latencies differed from the prolonged latencies found in other patients with loss of central nervous system myelin caused by vitamin B12 deficiency or multiple sclerosis.