Rajan S, Simon MV and Nair DG
Evoked potentials have been successfully monitored intraoperatively to provide valuable real-time information to surgeons and reduce unfavorable surgical outcome. However, the inability to reliably record Visual evoked potentials (VEPs) in the operating room continues to limit its use. Several factors - technical, anesthetic and others, have been looked into by various groups, but with limited success. Even when reliable waveforms were obtained, a correlation of intraoperative findings with postoperative visual function remained elusive. In this review, by systematically looking at how different groups have recorded VEPs intraoperatively over the years, we provide a comprehensive view of the methodology - anesthesia, recording parameters and stimulus delivery devices, and how they have possibly affected reliability of recording VEPs. We explore the use of newer techniques such as Diffusion tensor imaging, direct cortical recording and Optic nerve stimulation that supplement or improve the recording of VEPs. In addition, we discuss why intraoperative VEPs failed to predict post-operative visual outcome and offer suggestions to improve these limitations.
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