Interocular effect during visual acuity measurement with and without amblyopia

Purpose: Exploratory research to investigate the monocular change in visual acuity due to type of occlusion of the fellow eye (interocular effect) in amblyopes and nonamblyopes. Methods: The study design was a prospective convenience sampling of consecutive eye clinic patients with amblyopia/amblyogenic factors and visually normal volunteers. Participants were divided into two main groups based on entry-level visual acuity using clinical methods: amblyopes (≥2 lines interocular difference) and nonamblyopes. Ocular alignment, refractive error, stereoacuity, fixation status, and retinal correspondence were determined. The change in acuity of the nondominant eye based on two types of dominant eye occlusion (translucent, lightproof) was derived from a computer-generated acuity test using staircase methodology. Results: Some participants in each main group had an interocular effect of up to 0.15 logMAR. However, both overall group means did not show an improved visual acuity with one type of occlusion compared to the other. Subgroup analysis revealed a significant increase in the magnitude of interocular effect with esodeviations and abnormal retinal correspondence. Ansiometropic and strabismic amblyopes differed, showing monocular improvements with lightproof and translucent occlusion, respectively. Conclusions: Interocular effect related to the amount of light transmission allowed by the type of occlusion over the dominant eye may differ in amblyopia subtypes and increased magnitude of effect is related to the presence of esotropia and abnormal retinal correspondence.