Abstract
Purpose: :
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.
Methods: :
We have carried out a systematic investigation of the spatial properties of residual vision in a cohort of cortically blind patients (n=16) using forced choice detection of spatially and temporally modulated gratings. Based on detailed knowledge of the characteristics of residual visual processing we have devised a novel visual rehabilitation protocol incorporating repeated stimulation of cortically blind areas.
Results: :
We have demonstrated the presence of a narrow spatial channel of processing in 12 of the cases investigated. Also repeated stimulation in a group of 12 patients resulted in increased visual sensitivity within the field defect. There is also evidence for a modest, but significant shrinkage of the field defect as measured using standard perimetry.
Conclusions: :
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.
Keywords: visual impairment: neuro-ophthalmological disease