Intraoperative cortical VEP monitoring appears useful for the posterior visual pathway

This study used 1-Hz flashing light-emitting diodes and subdural strip electrodes to record the cortical responses of 17 consecutive patients who underwent microsurgical procedures for lesions near the posterior visual pathway. 

Initial visual evoked potentials (VEPs) were detected in 82 percent of all patients and in 94 percent of patients without total hemianopia in whom electrodes were placed sufficiently near the occipital pole. Initial VEP waveforms varied greatly from patient to patient, but in 11 patients they remained stable during surgery and the visual status did not change postoperatively. The detectability rates of the negative peak before 100 msec, positive peak around 100 msec, and negative peak after 100 msec, were 36 percent, 50 percent, and 100 percent, respectively, and the mean latencies and amplitudes were 90.0 msec and 61.0 μV; 103.9 msec and 34.3 μV; and 125.7 msec and 44.9 μV; respectively.

The studies' authors concluded that intraoperative cortical VEP monitoring is a potentially useful procedure to monitor the functional integrity of the posterior visual pathway.