JUN 04, 2012
This study published electronically by the journal Neuromodulation evaluated the temporal effects of transcranial direct current stimulation (TDCS) delivered to the occipital cortex on visual recovery in hemianopia patients. The authors followed patients undergoing vision restoration therapy (VRT) combined with active TDCS, and found that the addition of TDCS accelerated the recovery of stimulus detection. They conclude that TDCS may differentially affect the magnitude and sequence of visual recovery in a manner that is task specific to the visual rehabilitative training strategy employed.
The study included 12 patients previously diagnosed with unilateral postchiasmal visual field loss (hemianopia: seven; quadrantanopia: five) due to stroke (n = 10) or surgical trauma (n = 2). They were all in the chronic stage of recovery, with a mean time since the event of 39.83 ± 16.16 months. They were randomized to treatment with VRT combined with either active TDCS or sham TDCS.
VRT training comprised two half-hour sessions, three times a week for three months. The treatment presents light stimuli in the area of residual vision bordering on both the blind and intact visual fields.
Treatment with TDCS involves low current electrical stimulation directed to the occipital cortex through electrodes placed on the head and connected to a nine-volt battery driven stimulator.
The authors found that between-group differences in the rate of recovery of stimulus detection appeared within the first month of training. In contrast, a shift in the visual field border was only evident post-test (after three months of training). They also found that TDCS did not affect contrast sensitivity or reading performance.
These results demonstrate that upregulating the excitability of surviving visual networks within the occipital cortex by TDCS during VRT promotes improved visual rehabilitative outcomes following three months of training compared to VRT alone and resulted in earlier recovery of stimulus detection. However, these improvements were highly task specific and did not affect all measures of visual performance.
VRT previously has been shown to produce a mean shift in visual field border of five degrees and an increase in stimulus accuracy. However, these results are controversial and have been challenged.
This study and other research suggests that there are a variety of treatments that can be offered to patients with homonymous visual field defects that may result in greater improvement in visual field defects compared to the natural history of these cortical lesions.