Intraoperative monitoring of the visual evoked potential during endoscopic sinus surgery

Iatrogenic blindness resulting from conventional and endoscopic sinus surgery continues to be a major concern to the head and neck surgeon. A new electrophysiologic monitoring technique has been developed that can help avoid damage to the optic nerve and visual system. The approach involves monitoring the visual evoked potential with presentation of flash stimuli to the eyes. Thirty patients with chronic sinusitis underwent endoscopic sinus surgery with visual evoked potential monitoring. The procedures were carried out with patients under intravenous general anesthesia. Needle cortical electrodes were placed in the scalp. A modified light-emitting diode array/goggle was positioned in front of the patient's closed eyes. A triggered flash of 2 Hz was delivered through the goggle to stimulate the patient's retina. Cortical responses were amplified and averaged for 100 trials. Amplitude and peak-latency changes were monitored to alert the surgeon to any change in the visual response during the surgical dissection. Although no changes in response were noted during dissection, cold-water irrigation and reflected telescopic light could produce variations in the recorded responses, as will be discussed. Visual evoked potential monitoring may prevent a surgeon from continuing a bilateral procedure when there is indication of iatrogenic visual loss from dissection on the first side. Visual evoked potential also reassures the operator that no damage has occurred to the visual pathway at the conclusion of a case. Methods, case selection, operative technique, and documentation of monitoring will be discussed.