Efficacy of the visual evoked potential monitoring in endoscopic transnasal transsphenoidal surgery as a real-time visual function

Abstract

Background: Visual evoked potential (VEP) is used as a means of intraoperative visual function monitoring. It remains unclear, however, whether intraoperative VEP monitoring is a means of real-time visual function monitoring that has satisfactory effectiveness and sensitivity. To evaluate this, the relationships between VEP waveform changes in endoscopic transsphenoidal surgery and postoperative visual function were analyzed retrospectively.

Materials and methods: Intraoperative VEP monitoring was carried out during 82 endoscopic transnasal transsphenoidal surgeries for 164 eyes at Nara Medical University Hospital, Nara, Japan under total intravenous anesthesia. Red light flash stimulation was provided to each eye independently. The VEP recording and postoperative visual function were then analyzed.

Results: In 160 of 164 eyes (98%), steady VEP monitoring was performed. Stable VEP was acquired from eyes with a corrected visual acuity >0.1. VEP was not recorded in four eyes that had a corrected visual acuity under 0.05. A transient VEP decrease was observed in 26 eyes, 8 of which had improved visual acuity and 18 of which had no change in visual acuity. A permanent gradual VEP decrease occurred in eight eyes; this finding did not correspond to a change in visual function. The visual acuity of the patients who underwent the transsphenoidal operation in our study did not worsen.

Conclusion: Intraoperative monitoring of VEP predicts postoperative visual function, and a reversible change in VEP indicates that visual function will be preserved. Intraoperative VEP monitoring will be mandatory for surgeries harboring a risk of visual impairment.

Keywords: Intraoperative electrophysiological monitoring; visual acuity; visual evoked potential; visual field.