Impact of transcranial Direct Current Stimulation on stereoscopic vision and retinal structure in adult amblyopic rodents

Gema Martinez-Navarrete,1,2 Sergio Castaño-Castaño,3– 6 Miguel Morales-Navas,4 Francisco Nieto-Escámez,4,7 Fernando Sánchez-Santed,4 Eduardo Fernandez1,2 1Neuroprosthesis and Neuroengineering Research Group, Institute of Bioengineering (IB), University Miguel Hernández (UMH), Elche, 03020, Spain; 2Networking Research Centre of Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), Zaragoza, Spain; 3Department Psychology, University of Oviedo, Plaza Feijoo S/N, Oviedo, 33003, Spain; 4Department of Psychology, University of Almería, Ctra. Sacramento S/N, La Cañada de San Urbano, Almería, 04120, Spain; 5Institute of Neurosciences of the Principality of Asturias (INEUROPA), Oviedo, Spain; 6Institute of Health Research of the Principality of Asturias (ISPA), Oviedo, Spain; 7Neuropsychological Evaluation and Rehabilitation Center (CERNEP), Ctra. Sacramento S/N, La Cañada de San Urbano, Almería, 04120, SpainCorrespondence: Gema Martinez-Navarrete, Department of Histology and Anatomy (Faculty of Medicine). Neuroengineering Biomedical Research Group, Institute of Bioengineering, University Miguel Hernandez, Elche, 03202, Spain, Email [email protected] Sergio Castaño-Castaño, Department Psychology, University of Oviedo, Plaza Feijoo s/n, Asturias, 33003, Spain, Email [email protected]: The impact of visual deprivation on retinal structure is widely debated. Experimental models, like monocular deprivation through lid suture, provide insights into the consequences of lacking visual experience during development. This deprivation delays primary visual cortex (CV1) maturation due to improper neural connection consolidation, which remains plastic beyond the critical period. However, few studies have used Optical Coherence Tomography (OCT) to investigate structural alterations in the retina of animal models following monocular deprivation. Instead, some studies have focused on the ganglion cell layer using post-mortem histological techniques in amblyopia models induced by monocular deprivation.Methods: In this study, we used Cliff test to assess stereoscopic vision and spectral domain optical coherence tomography (SD-OCT) to evaluate retinal changes in an in vivo model of visual deprivation treated with Transcranial Direct Current Stimulation (tDCS).Results: The depth perception test initially revealed differences between individuals with amblyopia and the control group. However, after 8 tDCS sessions, amblyopic subjects matched the control group’s performance, which remained stable Additionally, significant changes were observed in retinal structures post-tDCS treatment. Specifically, the thickness of the Nerve Fiber Layer + Ganglion Cell Layer + Inner Plexiform Layer (NFL+GCL+IPL) increased significantly in amblyopic eyes (p< 0.001). Moreover, significant retinal thickening, including the Nerve Fiber Layer + Ganglion Cell Layer + Inner Plexiform Layer (NFL+GCL+IPL) and the entire retina, was observed post-tDCS treatment (p< 0.05), highlighting the critical role of tDCS in ameliorating amblyopia. Additionally, treated animals exhibited reduced thickness in the Inner Nuclear Layer (INL) and Outer Nuclear Layer (ONL).Conclusion: tDCS treatment effectively restores amblyopic individuals’ stereoscopic vision, aligning their performance with controls, while impacting retinal structure, highlighting its potential in ameliorating amblyopia’s visual deficits. Keywords: amblyopia, monocular visual deprivation model, tDCS, stereoscopic vision, OCT