Binasal hemianopia.

Three patients with nasal visual field defects are described. In each case it is believed that compression of the lateral fibres of the optic nerve by the anterior cerebral or internal carotid artery was the cause. Binasal hemianopia can thus be produced by a single lesion and is as much a true hemianopia as the common bitemporal one. The value of careful neuroradiological investigation to display the relationships of a tumour to the chiasma, optic nerves, and related vessels and thus explain the field defects is demonstrated.