Abstract
The most common visual defect to follow a lesion of the retrochiasmal pathways is homonymous hemianopia (HH), whereby, in each eye, patients are blind to the contralesional visual field. From a behavioral perspective, in addition to exhibiting a severe deficit in their contralesional visual field, hemianopic patients can also present implicit residual capacities, now usually referred to collectively as blindsight. It was recently demonstrated that HH patients can also suffer from a subtle deficit in their ipsilesional visual field, called sightblindness (the reverse case of blindsight). Furthermore, the nature of the visual deficit in the contralesional and ipsilesional visual fields, as well as the pattern of functional reorganization in the occipital lobe of HH patients after stroke, all appear to depend on the lesion side. In addition to their contralesional and ipsilesional visual deficits, and to their residual capacities, HH patients can also experience visual hallucinations in their blind field, the physiopathological mechanisms of which remain poorly understood. Herein we review blindsight in terms of its better-known aspects as well as its less-studied clinical signs such as sightblindness, hemispheric specialization and visual hallucinations. We also discuss the implications of recent experimental findings for rehabilitation of visual field defects in hemianopic patients.
Highlights
The most common visual defect to follow a lesion of the retrochiasmal pathways is homonymous hemianopia (HH), whereby, in each eye, patients are blind to the contralesional visual field
In a rehabilitation study of nine HH patients that we trained for detection, localization and identification of stimuli in the blind visual field, we demonstrated the feasibility of objective restoration of the contralesional visual field, and showed that it can be observed by conventional automated perimetry (Chokron et al, 2008)
The sense of vision cannot be reduced to the mere capacity to detect a visual stimulus or to visual acuity
Summary
The most common visual defect to follow a lesion of the retrochiasmal pathways is homonymous hemianopia (HH), whereby, in each eye, patients are blind to the contralesional visual field. The nature of the visual deficit in the contralesional and ipsilesional visual fields, as well as the pattern of functional reorganization in the occipital lobe of HH patients after stroke, all appear to depend on the lesion side. Lesions that occur between the optic chiasm and the primary visual cortex (V1) can provoke a type of visual deficit known as a cortical visual impairment. Such deficits translate to visual field defects or to more complicated visual defects, depending on the location of the lesion.
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