Evoked potentials in the evaluation of visual field defects due to chiasmal or retrochiasmal lesions

We used monocular full-field and hemifield pattern reversal stimulation to study visual evoked potentials (VEPs) in 20 patients with confirmed defects of the visual pathways. In 10 of 12 patients with homonymous field defects, it was possible to lateralize the brain lesion but not to predict the site of the lesion within the hemisphere. In four of eight patients with bitemporal field defects, VEPs suggested involvement at the chiasmal level. In the remaining cases, VEPs provided no correlation with perimetric and radiologic findings. We found that VEPs usually corroborated other diagnostic studies but subtle defects were not detected reliably, and large hemianopic defects were occasionally not lateralized accurately. VEP analysis is therefore of only limited value in assessment for clinical purposes of patients with homonymous or bitemporal hemianopias.