Visual field defects produced by basilar artery ectasia

The authors report two cases of visual field defects which are postulated to be due to the distal end of an elongated basilar artery compressing the visual pathways in the posterior suprasellar region. The mechanism of production of these defects is discussed, relating the abnormal position of the distal end of the basilar artery to a normally situated or only slightly post-fixed optic chiasm and optic tract and to a markedly post-fixed optic chiasm.