Visual Evoked Potentials. Black and white pattern reversal visual evoked potentials (PR-VEP) with a visual angle of 15 min of arc were recorded separately for each eye through silver–silver chloride cup electrodes placed over Oz and Cz (reference) with ground on the ear lobe. P100 latencies are reported for each PR-VEP. PR-VEPs performed at early onset of disease were bilaterally normal (t0). After one week (t1), P100 was absent on the left eye, but was still normal on the right eye. During follow-up, PR-VEPs showed gradual improvement on the left eye after eight days (t2), about one month (t3), and three months (t4) from the onset of disease. Finally a slight asymmetry of P100 latency was observed, increased by 10 ms on the left eye compared to the contralateral eye.