Visual evoked potential in patients with cerebral asthenopia

Cerebral asthenopia is often overlooked as a symptom in diffuse brain lesion. An objective correlate of this symptom has so far never been demonstrated. Averaged visual evoked potential (VEP) in 10 patients with asthenopia was compared with 20 normal subjects. Both eyes and each eye alone were stimulated using bipolar recording in the midline and over each of the occipital lobes. There was no difference of latency of the VEPs in the two groups, but the amplitude of the most prominent component was significantly reduced in the patients. There was also a difference in the two groups regarding habituation and lateralisation. No amplitude difference could be found in the somatosensory evoked potential. The amplitude difference in VEP, as an objective correlate of asthenopia, is probably modal specific and suggests involvement of the visual cortex. VEP is unsuitable as a diagnostic tool due to the great overlap between amplitudes in asthenopic patients and control subjects.