Surface Electrodes for Detection of Eye Movements during Skull Base Surgery—A Novel Monitoring Device
Eberhard Uhl, Walter Stummer, Michael Leo Strupp, E. Schröck, J.-C. Tonn · Skull base · 2005
Introduction: The purpose of the study is to report our experience with periorbital surface electrodes for neuromonitoring as a noninvasive method (electronystagmography) to monitor eye movements during skull base surgery. Material and Methods: Intraoperative electronystagmography was performed in 65 patients with tumors of the sellar and parasellar regions. Four electrodes were positioned periorbitally prior to surgery. A standard neuromonitoring unit (Nicolet Viking IV) was used to apply monopolar stimulation (0.1 to 1.0 mA, impulse 0.2 ms, frequency 4.7 Hz) to the eye motor nerves or tumor structures suspected of carrying neural structures. Results: Stimulation of eye motor nerves or suspected structures resulted in reproducible vertical and horizontal movements of the bulbus of the eye with a latency of 0.1 to 0.3 ms. The movements can be attributed to specific eye motor nerves. Conclusions: Although the method does not allow continous monitoring as an electromyogram (EMG) does, it suffices, since monitoring by direct stimulation of neural structures induces reproducible eye movements, which can help identify areas to be spared during tumor surgery. In contrast to EMG which requires intramuscular placement of needle electrodes, this method is easy to perform and since it is noninvasive poses no risk of ocular tissue injury.