visual field defect

a reduction in the normal extent of the visual field, characterized by partial or total blindness. This is caused by an interruption in the flow of visual impulses between the retina and the visual cortex, which may be caused by a lesion before, after, or in the optic chiasm or in all or a part of the optic radiations; it can involve tracts of one or both eyes. Each possible lesion produces a different defect.