Visual morbidity (visual acuity and/or visual field deficit) must be taken into account during neurosurgical procedures for lesions near the optical pathways. Part of this morbidity is due to surgical manipulation. There is no validated tool for intraoperative visual monitoring and few publications have studied this issue.

In a preliminary work based on analysis of these publications, we defined technical, anaesthetic and analytical parameters in order to optimise intraoperative visual evoked potentials monitoring. These parameters are special devices used for transpalpebral stimulation, complete intravenous anaesthesia without halogen or nitrous oxide, and pertinent analysis criteria of visual evoked potential (VEP). We suppose that these improvements will increase reliability of intraoperative VEP.

This genuine optimised monitoring in France, set up in association with Metrovision company, should help increasing intraoperative VEP reliability as a monitoring tool for visual pathways function.

In this study, we assess the predictive value of relevant intraoperative variations of VEP (more than 50% variation of latency and amplitude) on the visual prognosis at six months after surgery The visual assessment consisting of a visual field, a visual acuity, and the performance of pattern transient VEP, will be performed by an ophthalmologist before surgery, and at three and six months after surgery. An electroencephalogram with photostimulatory lighting will be used in pre-operative and will validate the absence of photo-induced epilepsy risk.

During the intervention, VEPs associated to an electroretinogram will be performed by a neurosurgeon trained to the use of these tools by Metrovision company:

• Under general anaesthesia, but before any surgery.
• During the surgery, at predetermined surgical times (while performing the craniotomy or the sphenoid opening, at various times during the perioptic lesion dissection, after the lesion resection, when closing).

Inclusion Criteria:

• Patients with lesion compressing or near the optical pathways

Exclusion Criteria:

• Patients with photic epilepsy