Evidence of dysfunction in the visual association cortex in visual snow syndrome

Patients with visual snow syndrome (VS) suffer from a debilitating continuous visual disturbance of unknown mechanism. The present study tested the hypothesis of dysfunctional visual processing using visual evoked potentials. Eighteen patients were compared to age-matched migraineurs (M) and healthy controls (C) using 2-way analysis of variance with group (VS, M, C) and gender as factors. Visual evoked potentials from patients with VS demonstrated increased N145 latency (in milliseconds, VS: 152.7 +/- 7.9 vs M: 145.3 +/- 9.8 vs C: 145.5 +/- 9.4; F = 3.28; p = 0.046) and reduced N75-P100 amplitudes (in microvolts, VS: 7.4 +/- 3.5 vs M: 12.5 +/- 4.7 vs C: 10.8 +/- 3.4; F = 3.16; p = 0.051). Dunnett post hoc analysis was significant for all comparisons between VS and controls. These findings are in agreement with the idea that the primary disturbance in VS is a dysfunction of the visual association cortex.