Cerebral blindness and plasticity of the visual system in children. A review of visual capacities in patients with occipital lesions, hemispherectomy or hydranencephaly.

This paper explores whether the child's visual system is more or less vulnerable than the adult's visual system, whether the capacity of the child's visual system to recover from cerebral blindness exceeds the capacity of the adult's, and which brain structures can mediate visual functions after damage to the geniculostriate visual system. Reports about the development of visual functions in normal and in visually-deprived children and about the recovery of visual functions after incomplete damage to the occipital lobe, unilateral hemispherectomy, and in the absence of both cerebral hemispheres in early life, are reviewed. In addition, 2 new cases are reported. A child (patient 1) is described, who was blindfolded, but had normal visual experience for 2 hours daily between the 24 and the 30 months of age. Despite the daily visual experience, there was an elevation of the luminance difference threshold (LDT) in the periphery of the visual field. An adult patient (patient 2) showed a special mode of "blindsight" that may be present in brain damaged children but that cannot be tested in young children. This patient was always able to detect targets correctly only by "feeling" their presence without actually seeing them. After damage to the geniculostriate system, lost visual functions reappeared in more than half of the children during visual-field training. In many children, the enlargement of the visual field exceeded the enlargement that was reported in hemianopic adults during visual-field training. In rare cases, visual targets were reliably detected in both visual hemifields, even after hemispherectomy.