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Introduction Unfavorable surgical outcome is a major concern when performing surgery around the visual pathway. Previously documented results on the usefulness of visual evoked potentials (VEPs) for intraoperative neuromonitoring (IONM) indicate their limited utility, mainly due to their instability and variability. We conducted this study at two different Hospitals in Spain, to evaluate the reproducibility of VEPs recording after implementing a number of methodological improvements. Methods Intraoperative VEPs were obtained from 36 eyes in 18 surgeries, including: 11 standard transsphenoidal pituitary surgery (STSS); four extended transsphenoidal surgery (ETSS) with supreasellar craniopharyngioma, sphenoid bone’s sellar region and orbital cavity lesions; and three occipito-parietal gliomas. Surgeries were performed altogether at the Ramon y Cajal University Hospital (Madrid) and Lozano Blesa Clinical University Hospital (Zaragoza). Total intravenous anesthesia (TIVA) with propofol was used in all cases. VEPs were elicited by LED goggle stimulation with stimulus duration of 15–20 ms, intensity of 2–3 cd/s.m-2 and repetition rate from 0.7 Hz to 2.1 Hz. In 17 cases, the recording scalp electrodes were placed at O1-Oz and O2-Oz, using lateral O1 (LO1-Oz) and lateral O2 (LO2-Oz) electrodes (5 cm left of O1 and 5 cm right of O2, respectively). In two cases, VEPs were obtained using subdural recording electrodes placed at the occipital cortex. Band pass filter setting was 1–3 Hz for the high pass filter and 300–1000 Hz for the low pass filter. All anesthetic regimens, and stimulation and recording protocols were the same at both centres. Results Baseline VEPs were obtained prior to first incision in all cases. In all cases, all waveforms were reproducible and remained stable throughout surgery, making it feasible for intraoperative neuromonitoring. A transient decrease in amplitude was noted in two cases. The surgeon was warned and the surgical procedure was temporarily halted, with subsequent VEP improvement in both cases. In the cases with subdural recordings, the reproducibility and stability were the same, but the amplitude of the VEPs was higher. None of the patients had worsening of postoperative visual function. Conclusion With the following mentioned modifications: (1) Total intravenous anesthesia; (2) Additional placing of scalp electrodes (LO1 and LO2); and (3) Montage selection with LO1, O1, O2 and LO2 referred to Oz; we have obtained reproducible and stable VEPs. Based on the results of our study, intraoperative VEPs are reproducible and reliable, and thus, suitable for intraoperative neurophysiological monitoring in surgeries where the visual pathway is at risk.

Objective The importance of visual evoked potentials (VEPs) in the field of Neurosurgery has been documented previously, but their use is not standardized due to their limitations (high sensibility to the anaesthetics and low reproducibility). In those surgical interventions that imply a possible damage to the optical nerve, VEPs may have an impact in the surgical decisions. Methods There have reviewed 6 cases from the Neurosurgery Department (Ramon y Cajal Hospital) which underwent surgery of tumours next to the visual pathway (in orbital cavity, occipito-parietal glioma, craniopharyngioma and at sphenoid bone’s sellar region). The visual function was monitored by VEPs with goggles stimulation and recording with the following electrode placing: Oz, O1, O2, lateral O1 and lateral O2. In two cases, responses were recorded with subdural electrodes. Results With the use of goggles with a stimulation frequency of 2.1 Hz, the placement of additional electrodes (lateral O1 and lateral O2), and the filters settings (low-pass filter: 1 Hz; high-pass filter: 1KHz), we have obtained reproducible VEPs in all the surgeries, with a higher amplitude with subdural recording. Discussion With these modifications in the neurophysiological technique, we have avoided one of the major difficulties using VEPs in the workaday monitoring, improving their reproducibility.