Combined Therapy of Bilateral Transcranial Direct Current Stimulation and Ocular Occlusion Improves Visual Function in Adults with Amblyopia, a Randomized Pilot Study

Abstract

Amblyopia is the interocular visual acuity difference of two lines or more with best correction in both eyes. Ocular occlusion therapy depends on neuroplasticity, and thus is effective in children but not in adult with later diagnoses. Transcranial Direct Current Stimulation (tDCS) is suggested to increase neuroplasticity. To determine if combined therapy of bilateral tDCS and ocular occlusion improves visual function in adults with amblyopia, we conducted a double blind randomized, controlled pilot trial in volunteers with amblyopia (ClinicalTrials.gov Identifier: NCT05016830). While applying ocular occlusion and performing a reading task, participants received sham bilateral tDCS or bilateral tDCS. Visual function and visual evoked potential were evaluated immediately after. 12 volunteers with amblyopia were randomized, 2 were excluded after misdiagnosis confirmation. A significant increase in visual acuity was observed after stimulation in the bilateral group (n = 5) versus the sham group (n = 5) along with a significant increase in visual evoked potentials amplitude in the amblyopic eye response. No significant changes were observed in stereopsis and contrast sensitivity. No volunteer reported any harm derived from the intervention. Our results suggest that bilateral tDCS might improve visual acuity in amblyopic adults through increasing neuroplasticity, which allows the therapeutic effect of ocular occlusion.