The visual evoked potential contrast response function in recovering optic neuritis

Abstract

VEP contrast response functions were obtained in 7 patients with recovered optic neuritis and in 6 age-matched controls. A 1.5 c/d sinusoidal grating was counterphase modulated at 4 Hz (8 reversals/sec) about a mean screen luminance of 141 cd/m². Grating contrasts ranged from 2% to 85% and were randomly presented. In all control observers, VEP amplitude was a nonmonotonic function of contrast; an amplitude inflection occurred between contrasts of 33% to 47% followed by a sharp increase in amplitude at higher contrasts. The slope of the function relating VEP phase to contrast was variable between observers at low contrasts but consistently “flat” at high contrasts. In spite of normal acuity and contrast sensitivity, VEP amplitude was severely attenuated at high contrasts in all optic neuritis eyes but there were no contrast-dependent phase abnormalities. The results were directed toward the issues of a) suprathreshold contrast processing in optic neurtis, b) relating a nonmonotonic VEP amplitude function to the contrast-segregating properties of single cells, and c) the relationship between VEP abnormalities and visual performance.