Restoration of vision with non-invasive electrical brain synchronisation after optic nerve damage

Objective: Partial visual system damage after stroke or trauma can be treated by repetitive training with visual stimuli („vision restoration therapy“, VRT). It is conceivable that improved visual functions are mediated by enhance synaptic transmission of surviving neuronal elements through LTP-like mechanisms of increased synaptic efficacy. To test this hypothesis we now studied if non-invasive repetitive stimulation of the damaged visual system with LTP-like low-level current bursts can also induce some vision restoration.

Methods: 446 patients with optic nerve lesion which was caused by either traumatic brain injury (TBI, n=209), inflammation (n=134), brain tumor (n=40) or vascular origin (n=63) were evaluated in an exploratory, open-label study. All patients underwent an ophthalmologic examination including visual acuity, perimetry and a retina evaluation with EEG examinations pre and post treatment. The electrical stimulation was carried out using a non-invasive device generating AC-current bursts with amplitudes <1000µA at 10–50Hz.

Results: Visual field enlargements were observed in 34.6% of the patients in the right eye and in 41.8% of the patients in the left eye. The size of the visual field of the right eye increased from 25.8±1.0% to 27.7±1.0%, i.e. an improvement of 1.9% (p<0.001) and in the left eye it was 2.3% (24.5±1.0% to 26.8±1.0%, p<0.001). The visual acuity of the right eye increased significantly from 0.23±0.02 to 0.25±0.02 (p<0.001) and the left eye from 0.22±0.02 to 0.23±0.02 (p<0.001). After a stimulation-free interval of nearly 7–8 months, the seeing field slightly decreased by 1.6% in the right eye and by 1.7% in the left eye (p<0.06 OD), but this change was non-significant in both eyes combined (p<0.095). After the second course of stimulation, the seeing area significantly increased again in the right eye (+1.2%, p<0.001) but not in the left eye (+1.3%, p<0.139).

Discussion: We propose that visual field enlargements in patients with visual field defects through electrical stimulation come about by increased neuronal synchronisation in higher visual centers. Our findings are compatible with the view that pulsed, repetitive, non-invasive stimulation induces LTP-like strengthening of synaptic transmission in residual tissue and thus restores some of the lost vision in patients with visual field defects. A well controlled clinical trial is now warranted.