RESIDUAL VISION WITH AWARENESS IN THE FIELD CONTRALATERAL TO A PARTIAL OR COMPLETE FUNCTIONAL HEMISPHERECTOMY

Two patients with unilateral disconnection or removal of the entire oc cipital lobe were tested for residual vision in their blind field. Usi ng image stabilization to eliminate eye motion artifacts, the central portion of each subject's visual field was tested, beginning 1 degrees from fixation and extending outward to 13.5 degrees. A narrow zone of residual vision was identified along the retinal vertical meridian of each patient. The lateral edge of this zone was generally within 3.5 degrees of the vertical meridian, though extended farther outward (but not beyond 6 degrees) at one field location for each subject. In one patient, it was present in both superior and inferior quadrants; in th e other, it was confined to the superior quadrant. Within their zones of residual vision, both patients could detect stimuli and perform sim ple shape discriminations, but could not name complex line drawings. T he patients were aware of their vision within this zone. No residual v ision, with or without awareness, was found in areas tested outside th ese zones. Given the complete absence of visual cortex contralateral t o the observed residual vision, alternate structures must be mediating these abilities. Copyright (C) 1996 Elsevier Science Ltd.