Evaluation of the Effects of Transorbital Alternating Current Stimulation in Patients with Methanol-induced Optic Neuropathy: A Case-Series Study

Objective: To evaluate the effects of transorbital alternating current stimulation (tACS) on the visual parameters of patients with methanol-induced optic neuropathy (MION). Methods: In this case series, patients with chronic MION who met the inclusion criteria were recruited for an interventional study. The patients were divided into two groups: group 1 (very severe vision loss: visual acuity worse than logMAR 2.3), and group 2 (mild-to-severe visual loss: visual acuity between logMAR 0.09 and logMAR 2.3). Ten daily sessions of tACS were applied daily for both groups. Visual acuity, contrast sensitivity, and visual-evoked potentials (VEPs) were measured before treatment and 3 weeks after the last day of stimulation. Results: Ten eyes in group 1 and 10 eyes in group 2 were included in the study. In group 1, the mean (±standard deviation [SD]) logMAR visual acuities were 2.62 (±0.23) and 2.53 (±0.36), pre- and post-stimulation, respectively ( P = 1.00). In group 2, the mean (±SD) logMAR visual acuities were 1.06 (±0.69) and 1.02 (±0.65) pre- and post-stimulation, respectively ( P = 0.85), while the mean (±SD) contrast sensitivity was 60 (±31.76) pre-stimulation and 56.6 (±26.1) post-stimulation ( P = 0.91). There were no significant differences in VEP parameters before and after treatment. Conclusion: tACS is not clinically effective in patients with MION, although subtle vision improvement was detected in 50% of patients in group 2. Treatment of MION is more challenging compared to other types of optic nerve neuropathies. This may be because of diffuse damage to the visual pathway and brain in methanol toxicity.