P 228. Repetitive transorbital alternating current stimulation (rtACS) alpha activity enhancement in patients with visual field deficits: a prospective, randomized, blinded, controlled, multicenter study

Abstract

Retrospective studies suggested that rtACS simulates neuronal activity and results in neuroplasticity ( Fedorov et al., 2011 ). Prospective, randomized, controlled studies in patients with pre-chiasmatic optic nerve damage showed that rtACS reduces visual field deficits, enhances vision-related Quality of Life ( Gall et al., 2011 ) and entrains rhythmic brain activity (Schmidt et al., 2012). This is understood to reflect periodic enforcing ( Zaehle et al., 2010 ) associated with the activation of residual vision resulting in restoration of visual field deficits ( Sabel et al., 2011 ). The objective of the present prospective multicenter study is to provide evidence that alpha power gain over occipital electrodes is a bio-marker that can predict visual field size improvement. 80 patients with pre-chiasmatic partial optic nerve damage were randomized prior to inclusion in the sham-stimulation controlled rtACS trial ( RCT ). The stimulation group (n = 44) received rtACS for 20–40 min/day on 10 consecutive days. Treatment parameters were defined daily (1) by subject specific amperage when patients have an obvious perception of phosphenes, (2) the strongest alpha frequency over occipital electrodes (lower cut-off) and (3) the flicker-fusion frequency (upper cut-off). The control group ( n = 36) received subliminal stimulation. Electroencephalographic (EEG) power spectra were assessed on each of the 10 days over the occipital cortex. The size of visual fields was measured before and after treatment with high resolution perimetry (HRP). Data analysis was non-parametric regression to account for the heterogeneous patient-population. The EEG data shows a systematic enhancement of alpha-power after stimulation ( p < .05). This effect is stronger in the treatment group as compared with the placebo group ( p < .05). Enhanced alpha-power was associated with reduced visual field deficits ( p < <.05). Clinical results are reported in a complementary abstract. The results confirm that rtACS entrains alpha-oscillatory brain activity and show that changes in brain-rhythms is associated with changes in the visual field size. Thus, EEG alpha-oscillations seem to provide a bio-marker that can predict adaptive processes in a visual system with a pre-chiasmatic lesion. Future studies should continue to address the optimization of rtACS as well as the stratification by etiology prior to clinical application in individuals or small populations. The study was co-funded by the EBS Technologies GmbH.