Direct epidural electrical stimulation of the optic nerve: a new method for intraoperative assessment of function

Abstract

Intraoperative visual system monitoring of lesions with a close relationship to the optic apparatus by using light flashes reportedly is difficult to perform, and the results are too unreliable to interpret. The authors used direct epidural electrical stimulation of the optic nerve (ON) during surgery instead of light flashes. Four patients were included in this feasibility study. In 3 patients-1 each harboring a planum sphenoidale meningioma, a tuberculum sellae meningioma, and an intraorbital ON sheath meningioma-2 stimulating needle electrodes were placed on each side of the ON just anterior to the optic canal, before unroofing the optic canal and an extradural anterior clinoidectomy. In the fourth patient, who harbored a frontotemporal astrocytoma, stimulation was applied at the exit of the ON from the canal. The electrically induced visual evoked potentials (eVEPs) were recorded from the scalp before, during, and after tumor removal. A typical eVEP consisted of N20 and N40 waves. The amplitude of the N40 wave varied up to 25% prior to tumor removal. In the patient with a symptomatic tuberculum sellae meningioma, the decompressive effect of opening the optic canal and the impact of manipulation during piecemeal tumor removal were detected by the eVEPs. In the patient with an ON sheath meningioma and light sensation, only the N20 wave was observed. Epidural electrical stimulation of the ON is a safe means of providing a stable signal and real-time information on nerve conduction during surgery. It may be a useful adjunct in improving visual outcomes postoperatively. Further clinical studies are necessary.

Vep

“…Still, the eVEPs recorded for this pilot study did detect the decompressive effect of opening the optic canal and the impact of surgical manipulation during tumor removal of a symptomatic tuberculum sellae meningioma. Though Bošnjak et al [ 37 ] felt such direct epidural optic electrical stimulation provided a stable signal and real-time information on nerve conduction during surgery and may be a useful adjunct to improving postoperative visual outcomes in procedures involving surgical removal of tumor and lesion in anterior visual pathway areas, he recognized that their sample was small ( n = 4) and that further clinical studies were needed to confirm the usefulness of this technique.…”

“…Direct Electrical Stimulation of Optic Nerve : Bošnjak et al [ 37 ] evaluated the feasibility and utility of recording scalp VEP responses to direct electrical stimulation (eVEP) of the ON during tumor removal surgery involving the anterior visual optic pathways and found the technique beneficial in preventing ON damage and improving outcomes. The typical eVEP consisted of N20 and N40 waves (see Fig.…”

“…Beneficial use of F-ERGs to monitor retinal function during eye surgery [ 32,33 ] and to assess the depth of anesthesia has been reported [ 35 ] . Others have employed direct ON stimulation for ON monitoring with good outcomes [ 36,37 ] . In addition, VEPs were reportedly helpful for anatomic navigation of the optic radiations by diffusion tensor imaging-based tractography for functional monitoring of the visual pathway [ 38 ] .…”

Optic nerve potentials and cortical potentials after stimulation of the anterior visual pathway during neurosurgery

“…The aim was also to relate cortical potentials to optic nerve potentials after flash and electrical epidural stimulation of ON in order to aid in the understanding of the origin of the visual system evoked potentials and to contribute to the development of intraoperative neurophysiological monitoring of visual function [15,[20][21][22][23][24][25].…”

Time to revisit VEP monitoring?

“…Contact lens type stimulators [7] have raised concern about corneal lesions [2]. High-intensity stimuli have brought some improvement [12]; direct electrical stimulation of the optic nerve is another promising suggestion [1]. Electroretinogram (ERG) controls for the presence of retinal signal generation [13].…”