Transorbital repetitive alternating current stimulation in patients with optic neuropathy

Purpose: Initial observations in clinical settings showed that electrical stimulation using non-invasive, repetitive transcranial alternating current stimulation (rtACS) applied transorbitally may improve visual functions in patients with visual impairments due to optic neuropathy. However, these data were not collected under strict experimental (control) conditions and have not been published internationally. Because of the potential significance of the mentioned observations, we initiated a single centre, prospective placebo-controlled, clinical study to evaluate the efficacy of rtACS in patients with optic neuropathy.

Methods: Patients were randomized to either the rtACS group (n=42 eyes) or a placebo group (n=20 eyes). Stimulation was carried out on 10 consecutive days using a non-invasive device generating AC-current bursts with amplitudes <1000µA at 10–50Hz. A 2-months follow-up was conducted.

Results: Analysing the post-treatment minus baseline differences of primary outcome measures significant increases of stimulus detection rates in visual field examination (rtACS group: 3% vs. placebo: 0.2%) and increases of visual acuity scores (rtACS group: 0.06 vs. placebo: 0.02 Landolt-C-Test) were observed in the rtACS group only with significant group differences compared to the placebo group. The increase of stimulus detection performance and visual acuity remained constant at a 2-months follow-up.

Conclusions: We propose that visual field enlargements in patients with visual field defects through non-invasive electrical stimulation may be due to increased neuronal synchronization in higher visual areas. Our results 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.