Abstract:
Full- and half-field visual evoked potentials (VEPs) are used to evaluate functional
effects of optic chiasm compression by pituitary tumours. Reduction in VEP amplitude,
typically from the temporal fields of vision, can occur even without demonstrable
clinical deficit. An inherent problem of prolonged or serial testing is that changing
levels of vigilance may affect the VEP. Gradual decrease in vigilance during a test
sequence or with serial testing may cause a reduction in amplitude of the response
mimicking the abnormality sought. This has serious implications when monitoring the
effect of medical treatment since it may give a false impression of tumour growth
requiring urgent surgery to prevent blindness. This report illustrates the nature
of the problem and describes techniques using electroencephalograms (EEG), which have
been used in an attempt to monitor vigilance. The ultimate aim is to produce a system
to automate such monitoring during VEP recording.
Keywords
EEG - Evoked Potentials - Vigilance - Monitoring
