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Transcranial direct current stimulation enhances recovery of stereopsis in adults with amblyopia - PubMed

Randomized Controlled Trial

Transcranial direct current stimulation enhances recovery of stereopsis in adults with amblyopia

Daniel P Spiegel et al. Neurotherapeutics. 2013 Oct.

Abstract

Amblyopia is a neurodevelopmental disorder of vision caused by abnormal visual experience during early childhood that is often considered to be untreatable in adulthood. Recently, it has been shown that a novel dichoptic videogame-based treatment for amblyopia can improve visual function in adult patients, at least in part, by reducing inhibition of inputs from the amblyopic eye to the visual cortex. Non-invasive anodal transcranial direct current stimulation has been shown to reduce the activity of inhibitory cortical interneurons when applied to the primary motor or visual cortex. In this double-blind, sham-controlled cross-over study we tested the hypothesis that anodal transcranial direct current stimulation of the visual cortex would enhance the therapeutic effects of dichoptic videogame-based treatment. A homogeneous group of 16 young adults (mean age 22.1 ± 1.1 years) with amblyopia were studied to compare the effect of dichoptic treatment alone and dichoptic treatment combined with visual cortex direct current stimulation on measures of binocular (stereopsis) and monocular (visual acuity) visual function. The combined treatment led to greater improvements in stereoacuity than dichoptic treatment alone, indicating that direct current stimulation of the visual cortex boosts the efficacy of dichoptic videogame-based treatment. This intervention warrants further evaluation as a novel therapeutic approach for adults with amblyopia.

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Figures

Fig. 1
Fig. 1

Experimental design. A sham-controlled, cross-over, double-blind study design was adopted. Group 1 (solid line) received anodal-transcranial direct current stimulation (a-tDCS) of the visual cortex during the first 5 treatment sessions and sham-tDCS (s-tDCS) during the second 5 sessions. The order of tDCS conditions was reversed for group 2 (dashed line). Visual functions were assessed before treatment (baseline), after 5 treatment sessions, and after 10 treatment sessions. tDCS was administered during the first 15 mins of dichoptic training. This was followed by two 25-min training blocks. A 5-min break was provided between each block

Fig. 2
Fig. 2

Overall improvements in visual function. (a, b) Stereopsis and amblyopic eye visual acuity measurements averaged across all 16 participants at baseline (Pre) and after 5 (post-5d) and 10 (post-10d) treatment sessions. *Significant change from baseline (p < 0.05, 2-sample paired t test). (c) Suppression measured as the Weber contrast that could be tolerated in the fellow eye when the amblyopic eye was presented with a random dot kinematogram (RDK) stimulus at 100 % contrast. Larger values indicate weaker suppression (less contrast difference between the eyes was required to overcome suppression). Error bars represent ± within-subject SEM. (d) Correlation between baseline visual acuity and change in visual acuity after 10 sessions. Each data point represents an individual participant. The positive correlation indicates that the treatment effect was smallest for participants with mild amblyopia and largest for those with more severe amblyopia

Fig. 3
Fig. 3

Mean stereosensitivity and visual acuity. Mean stereosensitivity (a) and visual acuity (b) for group 1 [open circles; anodal-transcranial direct current stimulation (tDCS) followed by sham-tDCS] and group 2 (filled circles; s-tDCS followed by a-tDCS) at baseline (pre) and after 5 (post-5d) and 10 (post-10d) days of dichoptic treatment. Dashed lines represent dichoptic treatment combined with a-tDCS and solid lines represent dichoptic treatment combined with s-tDCS. *Improvement in visual acuity from baseline (p < 0.05, 2-sample paired t test). # Improvement in stereopsis from pre to post-5d in group 1 and post-5d to post-10d in group 2 (p < 0.05). Error bars represent ± within-subject SEM

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