Effects of grating spatial orientation on visual evoked potentials and contrast sensitivity in multiple sclerosis

Previous studies suggest a delay of pattern visual evoked potentials (PVEPs ) in multiple sclerosis (MS) depending on grating orientation. We examined a group of 14 patients with definite MS recording PVEPs to vertical and hor izontal grating and analysing latency and amplitude of P60, N70 and P100 wa ves. We evaluated contrast sensitivity (CS) to dark and bright bars of seve ral spatial frequencies (SF). The aim was to evaluate the diagnostic value of evoked responses and CS in revealing involvement of cortical structures. PVEPs to 1 degrees cycle/degree (c/d) vertical bars were abnormal in 25% f or P60, in 32%;, for N70 and in 36% for P100; in 25% 36% and 42%;, respecti vely at 4 c/d, as regards horizontal bars at 1 c/d we found alterations of P60, N70 and P100 in 11%, 19% and 27% respectively: at 4 c/d in 19%, 27%, a nd 35%. CS resulted more abnormal for vertical grating, with a maximum impa irment for 3.7 c/d SF. We may conclude that the use of vertical grating in clinical routine is more reliable both for PVEPs and CS testing; in additio n CS can be abnormal even with normal PVEPs: this could mean an early impai rment of CS and provide useful indications about a subclinical involvement of visual cortex.