Treatment and Characteristics of Interocular Suppression in Amblyopia

Abstract

AIMS: Amblyopia is a common neurodevelopmental visual disorder usually treated in early childhood, but many children are left with residual visual deficits. Treatments are rarely offered to older children and adults due to an assumed lack of neuroplasticity. Active cortical interocular suppression of the amblyopic eye has been hypothesised to underlie amblyopic visual deficits. Binocular contrast-balancing treatments to target suppression appeared to be effective in pilot studies including adults and children. This treatment method assumes that interocular suppression in amblyopia is an unbalanced form of normal interocular suppression. METHODS: A multi-centre, double-masked, randomised clinical trial (the Binocular treatment for amblyopia using videogame [BRAVO] study) was conducted to compare an active contrast-balancing binocular videogame with a placebo videogame for home-based treatment of unilateral amblyopia in children ≥7 years and adults. Standard pre-randomisation optical treatment procedures were applied in all age groups. A second project (the Mechanisms of amblyopia [MOA] study) used psychophysical methods to investigate the qualitative characteristics of interocular suppression in adults with amblyopia compared to adults with normal vision. RESULTS: The BRAVO study included participants aged 7-55 years. Eighty-two participants completed the optical treatment phase. Twenty-five (30%) improved by ≥0.10 logMAR in amblyopic eye visual acuity (VA), and 15 (18%) improved by ≥2-octaves in stereoacuity. Age was not significantly associated with magnitude or likelihood of improvements. The videogame phase included 115 participants. The active videogame did not significantly reduce interocular suppression (p=0.17) or improve visual functions more than placebo (amblyopic eye VA improvements: active group 0.06 ± 0.12 logMAR, placebo group 0.07 ± 0.10 logMAR; p=0.25). The MOA study revealed that some patients with amblyopia have suppression characteristics distinct from normal vision, which suggest the presence of different, pathological suppression mechanisms. Suppression characteristics could not be predicted from available clinical measures. CONCLUSIONS: Individual differences in suppression mechanisms require further investigation, and may need individually tailored treatment strategies. Though the home-based binocular videogame treatment investigated was not more effective than placebo, other contrast-balancing strategies may still be effective. Optical treatment, the simplest form of binocular therapy, appears to be effective for a subset of older children and adults with amblyopia.