Light modulation perception test in multiple sclerosis

A method for testing visual sensitivity to modulated sources have been developed. The method differs from critical frequency fusion test for the pattern of stimulation. A triangular function generator modulates the luminance of a solid state lamp (green or red); the frequency is varied from 50 Hz to 1 Hz values until the subject perceives distinctly a periodic variation of luminance. The trial is repeated for different amplitudes of modulatìon. This kind of stimulation simplifies most of the problems of standardization of other techniques due to stimuli duration, time interval, and mean level of luminance. Twenty normal subjects and twenty patients with multiple sclerosis have been evaluated and the results have been compared with visual evoked potentials to pattern stimulation. The patients with multiple sclerosis did not show any visual acuity defect or field abnormality at the moment of the test. In the normal subjects the maximum of sensìtivity was between 8 and 12 Hz independently of the mean luminosity of the source. No clear differences were found between red and green lìght, however in normal subjects foveal perception for red light modulation seems to have a lower threshold. Twelve patients showed an abnormal sensitivity to the light perception and 15 had a delayed visual evoked responses to pattern stìmuli. We conclude that the light modulation perception test (L.M.P.) is a simple and easy handling method for subclinical visual defects detection