From unconscious to conscious vision: Rehabilitation of a case of cortical blindness
Dr Clemence BOURLONa, Dr Marika URBANSKIb
a Clinique Les Trois Soleils, Boissise le Roi, France, b Hôpitaux de Saint-Maurice, Saint Maurice, France
Introduction: Cortical blindness is defined as a loss of conscious visual sensation caused by damage to the primary visual cortex or its postchiasmal afferents. Such a deficit is followed by a period of plasticity that rarely lasts beyond 6 months and is thought after to be stable and permanent. These patients behave as if they were blind, without being able to distinguish movements or changes in brightness. However, we observe a residual visual treatment process among some patients. The conscious perception is either altered or absent (i.e. the "blindsight" phenomenon)1. This residual vision may be the basis for appropriate neurovisual rehabilitation2.
Observation: Mr N. is a 42 years-old right-handed male, admitted to our rehabilitation unit after a posterior reversible encephalopathy syndrome. The lesion analysis highlights a bilateral lesion of visual areas and the fusiform gyrus and the right inferior temporal gyrus. Mr N. presents a complete cortical blindness without anosognosia. Rehabilitation is based on the stimulation of residual processing abilities (blindsight). First, perception of brightness changes as well as movements and colors are recovered. After 6 months, the conscious perception of simple shapes becomes possible and after 1 year, Mr N. begins to perceive letters. A Goldmann visual field examination revealed recovery of a part of the right visual field. After 2 years, the conscious perception of objects becomes possible and the visual field continues to improve.
Discussion: Improvement of visual perceptual abilities following a cortical blindness appears thanks to an appropriate rehabilitation and continues 6 months post-lesion. The use of alternative subcortical pathways (direct route colliculo-pulvinar to V5 and direct lateral geniculate nucleus to V4)3, reported in blindsight phenomenon, might suggest a recovery of a conscious vision.
1. Weiskrantz, L., Blindsight revisited. Curr Opin Neurobiol, 1996;6: 215-20.
2. Vanni, S., et al., Dynamics of cortical activation in a hemianopic patient. NeuroReport 2001;12:861-5.
3. Urbanski, M., O.A. Coubard, and C. Bourlon, Visualizing the blind brain: brain imaging of visual field defects from early recovery to rehabilitation techniques. Frontiers in Integrative Neuroscience 2014; 8: 74.
Keywords : cortical blindness, rehabilitation, neuropsychology, blindsight