JLE

Revue de neuropsychologie

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Homonymous hemianopia: visual field defect, implicit perception and hallucinations Volume 6, issue 4, Octobre-Novembre-Décembre 2014

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Authors
1 Fondation ophtalmologique Rothschild,
Service de neurologie,
Unité fonctionnelle vision et cognition,
25, rue Manin, 75019 Paris, France
2 Université Paris-Descartes,
Laboratoire de psychologie de la perception,
UMR 8242, CNRS, 75006
France
3 Fondation ophtalmologique Rothschild,
Service de neurologie,
Paris, France
4 Fondation ophtalmologique Rothschild, Service d’imagerie, Paris, France
5 Fondation ophtalmologique Rothschild, Unité neurovasculaire, Paris, France
* Correspondance

Homonymous hemianopia (HH) is a neuro-visual disorder where patients do not see stimuli presented in the contralesional visual field (VF). HH is the most frequent cortical visual impairment after stroke. HH is often associated with difficulties in reading, spatial organization, visuo-spatial exploration, processing a visual scene in its entirety as well as to the impossibility to drive. Whereas residual vision in the contralesional (blind) VF has been extensively studied, the quality of vision in the ipsilesional VF remains misinformed. Hemianopic patients present a loss of vision in the visual field controlateral to the post-chiasmatic lesion. Hemianopic patients may, however, present unconscious, implicit visual capacities in their ‘blind’ contralesional visual field. These capacities were described at the beginning of the 20th century and labeled “blindsight” by Weiskrantz in 1974. The neuro-anatomical correlates of “blindsight” still remain controversial at the moment. Furthermore, hemianopic patients may present visual hallucinations in their blind field, the physiopathological mechanisms of which remain still questioned. In addition, we were recently able to highlight the incidence of the occipital lateralization on visual processing in the central visual field of hemianopic patients. According to recent neuroimaging studies, the lesion side seems also to determine the pattern of functional reorganization in the occipital lobe after stroke. These recent studies also highlighted the presence of an ipsilesional visual field disorder (sightblindness) in hemianopic patients. Regarding the diversity of visual disorders in hemianopic patients, HH represents an interesting pathological model of vision to study the complex role of the primary visual cortex in vision. Undoubtedly, this amount of clinical and experimental evidence will have important repercussion at the theoretical as well at the clinical level.