Intraoperative monitoring to preserve central visual fields during occipital corticectomy for epilepsy.

Photic driving using a flashing strobe light was recorded via intracranial electrodes in two patients with occipital epilepsy being evaluated for surgery. The same technique was used to monitor the visual cortex intraoperatively. Visual evoked potentials (VEPs) were also obtained using the intracranial electrodes in one patient. Preoperative photic driving occurred in a separate location from the cortical areas producing ictal epileptiform activity. VEPs were located in the same site as photic driving. Photic driving was monitored throughout the resection and remained unaffected at the end of each procedure. Postoperative visual field testing in both patients showed preservation of central vision although some reduction in peripheral fields was seen. Intraoperative monitoring of the visual cortex using photic stimulation proved to be a reliable technique for preserving central vision during occipital lobe surgery.