Restorative and compensatory therapy approaches in cerebral blindness - a review

In the first part of this review, different types of homonymous Visual Field Disorders (VFDs) and their resulting visual disabilities are analyzed in 313 patients with VFDs and 141 patients without VFDs from a neurorehabilitation centre for adults. Homonymous hemianopia was the most frequent visual field loss (54.7 %), followed by hemiamblyopia (23.3 %), quadrantanopia (15.3 %) and paracentral scotomata (6.7 %). About 70 % of all VFD patients had a visual field sparing of 5 degrees or less (macula or foveal sparing). Patients with VFDs frequently showed two types of disabilities: hemianopic alexia was subjectively reported and objectively found in 50-90 % of all patients, and visual exploration deficits in the scotoma were complained and found in 17-70 % of the VFD patients. While hemianopic alexia was related to parafoveal visual field sparing, and additionally to visual acuity in patients with bilateral VFDs, visual exploration deficits were correlated to the size of the area in the scotoma in which the patient searched for a stimulus with saccadic eye movements (search field). The size of the search field in the intact hemifield was not related to visual exploration deficits in unilateral VFDs. As a third disability, visual-spatial deficits in VFD patients are summarized. In the second part, restorative and compensatory treatment approaches for postchiasmatic VFDs are reviewed. Partial restitution of blind regions in the visual field is achieved in the majority of patients treated with purely restorative methods including saccadic localization or light detection in the scotoma. However, the amount of the visual field recovered is limited to 5-12 degrees (mean) in 90 % of these patients. Compensatory treatments seek to improve the substitution of the lost field region by large-scale saccadic eye movements to the scotoma, spatially organized search strategies in both visual hemifields, and by training small-scale eye movements required for reading. Significant improvements in these areas are achieved in 95 % of all VFD patients with these treatment techniques, with documented transfer to visually related activities of daily living. Furthermore, a significant though limited visual field increase of 5-7 degrees is achieved in 30-50 % of patients treated in this way. In the final section, promising approaches that might lead to new treatment techniques for VFDs are reviewed. Among these are the gaze-dependant modulation of scotomata, training-dependant enlargement of the useful field of view, a nd t he uncovering of residual visuomotor capacities to visual stimuli in a scotoma.