Visual scanning behavior in patients with homonymous hemianopia

Abstract

This study examined oculomotor scanning behavior in 60 patients suffering from homonymous hemianopia due to postgeniculate damage. Eye movements were recorded using an infra-red recording technique during performance of a visual searching task. In 24 patients (40%) scanning behavior was found to be normal; the remaining 60% showed significantly increased search times. Detailed analysis of patients' eye movements revealed that the pronounced slowing of visual scanning was mainly due to the disordered spatial organization of scanning not only in the affected, but also, to a lesser degree, in the intact hemifield. CT and NMR examination revealed that additional damage to the ipsilateral posterior thalamus or the parieto-occipital cortex results in impaired spatial organization of visual scanning. A smaller group of patients (n = 14) with impaired visual scanning was treated to improve the spatial organization of visual exploration. After training, all patients showed a significant improvement in visual searching, indicating that successful oculomotor adaptation can substitute the lost visual hemifield. It is argued that impaired visual scanning in hemianopic patients is mainly caused by visual spatial disorientation which also affects spatial integration of visual information processing.