Real-time monitoring of visual evoked potentials.

Steady-state visual evoked potentials (SSVEP) were recorded in response to flashes from eyepatch-mounted light-emitting diodes during neurological surgery and in the intensive care unit. SSVEP were detected and measured with a microprocessor-based waveform correlator. The system enabled a continuous display, in real time, of SSVEP amplitude and latency. SSVEP amplitude and latency changes were monitored throughout a variety of surgical procedures. Some of these procedures directly affect the central visual pathway, some affect the central nervous system as a whole, while others do not affect central nervous system function. In addition, intensive care unit patients with a variety of intracranial pressures were monitored. The results of this study indicate that SSVEP recorded with this method showed changes in SSVEP within seconds of surgical and/or medical decompression of intracranial pressure and were sensitive to specific changes in the visual pathway. Surgical procedures that directly affected the visual system, or elevation of intracranial pressure, resulted in changes in SSVEP. In contrast, procedures that did not affect the functional integrity of the visual system did not affect the recordings.