Fig. 20. Prolonged pattern visually evoked potential (VEP) following optic nerve involvement. The VEPs were elicited by 30-minute checks reversing at 2 Hz and were recorded with the active electrode 5 cm above the inion referred to the right ear. The patient, a 27-year-old white male, had a history of optic neuritis in the right eye. The VEP elicited from the right eye (OD) is prolonged in latency relative to laboratory norms and the left eye (OS).