Beyond monocular acuity: Resolving the amblyopia treatment paradox with mechanism-targeted outcomes and modern testing methods

Amblyopia is a neurodevelopmental disorder affecting approximately 1%-5% of the population and has traditionally been treated based on reduced monocular visual acuity. However, growing evidence indicates that amblyopia involves broader deficits spanning low- and high-level visual processing, many of which persist even after successful acuity restoration and cannot be explained solely by acuity loss of the poor eye.

Despite the expanded understanding and the development of binocular (dichoptic) therapies designed to rebalance interocular suppression, clinical trials over the past decade comparing binocular and occlusion therapies have remained largely focused on monocular visual acuity gains. Measures of binocular function were typically limited to coarse clinical stereoacuity tests, which lack the sensitivity needed to detect subtle yet meaningful functional improvements. This therapeutic paradox-targeting binocular mechanisms while evaluating outcomes mainly through monocular acuity-constrains our ability to properly assess emerging interventions. In this review, we summarize multilevel dysfunctions in amblyopia, evaluate outcome measures used in binocular therapy trials, and outline modern testing methods for rapid and clinically feasible assessment of binocular and higher-level visual functions. We propose a tiered framework for outcome selection that balances mechanistic relevance with feasibility by retaining visual acuity alongside at least one quantitative measure of binocular balance or suppression and one sensitive stereopsis assessment, with additional measures included when relevant to the intervention. We also highlight the need for open-source tools, standardized protocols, and reproducible research practices to improve accessibility and cross-study comparability of different testing methods for evaluating multi-level impairments in amblyopia.

Advances in the understanding of amblyopia and the development of mechanism-targeted binocular therapies require a corresponding shift in how treatment outcomes are evaluated. Reliance on monocular acuity alone is insufficient to capture the broader functional deficits and recovery processes associated with amblyopia. A flexible, mechanism-driven, and clinically feasible testing strategy using a battery of tests is needed to align outcome measures with therapeutic targets and to better evaluate functional recovery across multiple domains of visual processing.