The goal of this randomized, double-blind clinical trial is to determine whether transcranial direct current stimulation (tDCS) can effectively and safely improve vision in children aged 4-14 years with strabismic or anisometropic amblyopia that has not responded to conventional patching therapy.

The main questions it aims to answer are:

Does tDCS produce significant and sustained improvements in visual acuity, contrast sensitivity, and stereopsis in children with amblyopia?

Is tDCS a safe, well-tolerated, and faster alternative or complementary treatment compared with standard occlusion therapy?

Does tDCS induce functional and structural changes in the visual cortex associated with increased neuroplasticity, including modulation of GABAergic activity?

If there is a comparison group:

Researchers will compare active tDCS with sham (placebo) stimulation to see if active treatment leads to greater visual recovery and cortical changes than placebo.

Participants will:

Receive several sessions of active or sham tDCS using low-intensity electrical stimulation applied to visual brain areas.

Undergo standard visual assessments, including visual acuity, contrast sensitivity, and stereopsis.

Complete neurophysiological and neuroimaging evaluations (EEG, pattern visual evoked potentials, and functional MRI).

Provide biochemical measures related to GABA levels.

This study aims to validate tDCS as a non-invasive, child-friendly, and effective therapy that may overcome the limitations of patching and support its inclusion in paediatric clinical practice.

Amblyopia is a neurodevelopmental visual disorder characterised by reduced visual performance despite optimal optical correction and the absence of ocular pathology. It affects up to 2-4% of children and is the leading cause of visual impairment in this population. Conventional treatment involves optical correction and patching of the contralateral (non-amblyopic) eye, which usually produces limited improvement, low therapeutic compliance and frequent relapses, highlighting the need for new approaches based on neuroplasticity.

Transcranial direct current stimulation (tDCS) is a non-invasive neuromodulation technique that can modify cortical excitability by regulating GABAergic inhibition in the primary visual cortex (V1). It has been safely used in children with attention deficit disorder, schizophrenia, epilepsy or cerebral palsy.

Preliminary data from our group show that after three sessions of tDCS on paediatric strabismic amblyopia, there are significant and sustained improvements in visual acuity, contrast sensitivity, and stereopsis at 3 months.

This project proposes a randomised, double-blind clinical trial to evaluate the efficacy, safety and optimal dosage regimen of tDCS in children aged 4 to 14 years with strabismic or anisometropic amblyopia classified as non-responsive to occlusion therapy, according to the criteria established by the Pediatric Eye Disease Investigation Group (PEDIG). Objective biomarkers will be included using electroencephalogram, visual evoked potentials (pattern) and functional magnetic resonance imaging to explore cortical functional and structural changes, together with biochemical assessment of GABA levels.

The expected outcome is to validate tDCS as an effective, rapid, and safe alternative or complementary therapy for amblyopia. Demonstrating sustained visual and cortical improvements would support its inclusion in paediatric clinical protocols and promote translational neuro-ophthalmological rehabilitation

Inclusion Criteria:

• Children aged 4-14 years.
• Strabismic amblyopia resistant to patching (PEDIG criteria).
• Anisometropic amblyopia resistant to patching (PEDIG criteria).

Exclusion Criteria:

• Ocular pathology.
• Nystagmus.
• Mental disability.
• Cognitive delay.
• Neurological problems incompatible with treatment.
• Pacemakers.
• Intracranial electrodes.
• Implanted defibrillators.
• Cranial pathologies.
• Cranial lesions.
• Withdrawal will occur upon adverse events, protocol deviation, refusal, or loss to follow-up.