Activating blind fields in hemianopics with moving stimuli potentiates visual field enlargements as induced by Vision Restoration Therapy (VRT): a cross-over-study

Background: Vision restoration therapy (VRT) is used by hemianopics to enlarge visual fields and it uses a single-point visual training paradigm in areas of residual vision, i.e. in the border region of the visual field defect. We now studied the question if efficiency of VRT can be increased when the entire region of blindness is simultaneously stimulated by a massive moving spiral stimulus which is aimed at activating extrastriate pathways left intact after the cortical damage.

Methods: Patients (n=18) had already been treated with VRT for at least 6 months prior to study entry and many had already experienced prior visual field enlargements. They were randomly assigned to one of two groups: Group 1 (n=8) first received enhanced VRT (eVRT) for a 3 month period 1h/daily and then conventional VRT for another 3 months. Group 2 (n=10) trained in inverse sequence (VRT/e-VRT). E-VRT is an intense visual training where – in addition to the traditional VRT-stimulation – the entire blind field is simultaneously stimulated by a large spiral moving centripetally at white/black bar alternating frequency of 10Hz; conventional VRT stimulates only the border region of the visual field defect with a single-point-stimulation.

Results: Stimulus detection performance in group 1 improved from 52.4% to 58.3% after e-VRT, i.e. an absolute improvement of 5.9% (p<0.01). After the second training period (VRT) the number of detected stimuli further improved by 1.8% (p<0.05). Detection performance in group 2 improved after the first training period (VRT) from 51.8% to 54.7%, i.e. a 2.9% change (p<0.05) and also 2.9% after e-VRT, i.e. from 54.7% to 57.6% (p<0.05). Fixation performance in group 1 declined by -5% after e-VRT whereas it was unchanged (+0.5%) after VRT. In group 2 fixation performance improved by 4.1% after VRT and declined by 2.3% after e-VRT. All changes in fixation performance were unrelated to visual field enlargements. Reaction times did not differ before vs. after the training in either group or training. The detection performance was significantly greater (p<0.05) after e-VRT (4.2%) than after VRT (2.4%).

Conclusion: The potentiation of vision restoration by eVRT is interpreted as an activation of extrastriate pathways by massive “spiral-like“ visual stimulation. These pathways by-pass the damaged visual cortex and stimulate extrastriate cortical regions in a “blindsight“-like phenomenon. The loss of fixation performance in the eVRT group did not correlate with the visual field enlargements and thus cannot explain the enhanced restoration. We interpret our results as indirect evidence that extrastriate visual areas are involved in vision restoration and their activation potentiates the efficacy of VRT.