Blindsight and visual rehabilitation in the cortically blind

Lesions of the occipital cortex can result in areas of cortical blindness affecting the corresponding regions of the patient's visual field. The traditional view is that, aside from limited, acute and spontaneous recovery, such areas of blindness are absolute and permanent. It has been found, however, that within such field defects some residual visual capacities may persist. These residual capacities are termed blindsight. Using both psychophysical and pupillometric techniques we investigate residual spatial properties within blindfield of a cohort of cortically blind patients (n=16). Using forced-choice detection of spatially and temporally modulated gratings we demonstrated the presence of a narrow spatial channel of processing in 12 of the cases investigated. The pupillometric data are also in agreement with the psychophysical findings. On the basis of the characteristics of residual visual processing, a visual rehabilitation protocol has been devised incorporating repeated stimulation of cortically blind areas. In a group of 12 patients, an increased visual sensitivity within the field defect was demonstrated. These findings suggest that (a) blindsight in cases of cortical blindness may not be a rare phenomenon, and (b) repeated stimulation based on appropriate visual stimuli may result in improvements in visual sensitivities.