Effects of luminance on the pattern visual evoked potential in multiple sclerosis.

Pattern visual evoked potentials (PVEPs) were recorded at 5 levels of luminance from 26 patients with multiple sclerosis and from age-matched normal subjects. In normal subjects, the latency of both the major positive peak (P100) and the early positive peak (P60) was an inverse logarithmic function of pattern luminance. The increase in latency per unit log decrease in luminance was 12.1 msec for P100 and 5.7 msec for P60. Only 2 patients had entirely normal results. In 9 patients, the increase in latency of P100 per unit log decrease in luminance was abnormal. Of the 18 luminance-latency functions obtained from testing both eyes, 10 were abnormal, 6 showing a greater than normal increase in latency with decreasing luminance and 4 a less than normal increase. The 6 luminance-latency functions with a greater than normal increase in latency with decreasing luminance were all from patients without other evidence of optic nerve involvement. Pattern luminance, therefore, as well as patient selection, can significantly affect the proportion of abnormal PVEP latencies in any group of patients with possible, probable or definite multiple sclerosis. The abnormal response of the PVEP to changes in luminance and the different effects upon P100 and P60 indicate that the delayed PVEPs in patients with multiple sclerosis cannot be attributed solely to slowing of conduction in the optic nerve.