To clarify the usefulness of intraoperative monitoring of visual evoked potentials (VEPs) in aneurysm surgery, we examined the correlation between the VEP amplitude and postoperative visual function in patients who underwent aneurysmal clipping.
We developed a new light-stimulating device and introduced electroretinogram (ERG) to ascertain retinal light stimulation under total venous anesthesia. The new stimulating device consists of 16 red light-emitting diodes embedded in a soft silicon disk to avoid deviation of the light axis after frontal scalp-flap reflection. Under total venous anesthesia with propofol, ERG and VEP were recorded in 50 patients who were at intraoperative risk for visual impairment. Stable ERG and VEP recordings were obtained in 98 eyes. In one eye, stable ERG was recorded but VEP could not be obtained, because the eye manifested severe preoperative visual dysfunction. In the another eye, the disappearance of ERG and VEP after frontal scalp-flap reflection suggested technical failure attributable to deviation of the light axis. The criterion for amplitude aggravation was defined as a 50% decrease in amplitude compared to the control level. Of 93 eyes without amplitude changes, 2 manifested improved visual function postoperatively and 91 showed no change. Of 3 eyes with intraoperative VEP deterioration and subsequent recovery upon changing the operative maneuver 3 exhibited no change. The VEP amplitude decreased without subsequent recovery to 50% of the control level in both eyes of 1 patient, and she developed homonymous quadrant hemianopsia postoperatively.
With the strategy introduced here it is possible to record stable VEP in almost all cases without severe visual dysfunction. In some patients, postoperative visual deterioration can be avoided by intraoperative VEP monitoring. All patients without an intraoperative decrease in the VEP amplitude were without postoperative deterioration in visual function, suggesting that intraoperative VEP monitoring may help to prevent postoperative visual dysfunction in aneurysmal clipping.
