Vision recovery with perceptual learning and non-invasive brain stimulation: Experimental set-ups and recent results, a review of the literature

BACKGROUND: Vision is the sense which we rely on the most to interact with the environment and its integrity is fundamental for the quality of our life. However, around the globe, more than 1 billion people are affected by debilitating vision deficits. Therefore, finding a way to treat (or mitigate) them successfully is necessary. OBJECTIVE: This narrative review aims to examine options for innovative treatment of visual disorders (retinitis pigmentosa, macular degeneration, optic neuropathy, refractory disorders, hemianopia, amblyopia), especially with Perceptual Learning (PL) and Electrical Stimulation (ES). METHODS: ES and PL can enhance visual abilities in clinical populations, inducing plastic changes. We describe the experimental set-ups and discuss the results of studies using ES or PL or their combination in order to suggest, based on literature, which treatment is the best option for each clinical condition. RESULTS: Positive results were obtained using ES and PL to enhance visual functions. For example, repetitive transorbital Alternating Current Stimulation (rtACS) appeared as the most effective treatment for pre-chiasmatic disorders such as optic neuropathy. A combination of transcranial Direct Current Stimulation (tDCS) and visual training seems helpful for people with hemianopia, while transcranial Random Noise Stimulation (tRNS) makes visual training more efficient in people with amblyopia and mild myopia. CONCLUSIONS: This narrative review highlights the effect of different ES montages and PL in the treatment of visual disorders. Furthermore, new options for treatment are suggested. It is noteworthy to mention that, in some cases, unclear results emerged and others need to be more deeply investigated.