Sensory Eye Dominance Remains Stable Across Binocular Combination and Rivalry in Normal and Anisometropic Amblyopic Vision.

Purpose: When dichoptically presented with sinewave gratings of equal but opposite orientations, observers' binocular perception transitions from combination to rivalry as interocular orientation difference increases. This study aimed to investigate whether sensory eye dominance (SED) is modulated by interocular orientation differences in amblyopic and healthy adults. Methods: Eight adults with amblyopia (26.25 ± 3.96 years, 5 women) and 10 adults with normal vision (25.00 ± 1.56 years, 5 women) participated. Dichoptic sinewave gratings were presented with six interocular orientation differences (9 degrees, 18 degrees, 36 degrees, 54 degrees, 72 degrees, and 90 degrees) across three spatial frequencies (0.5 cycle per degree [cpd], 2 cpd and 4 cpd). SED was quantified using a binocular orientation discrimination task. Balance point (BP), defined as the log contrast ratio yielding equal (50%) perceptual dominance, was compared across all conditions. Results: BPs showed no significant variation across orientations in either group (healthy: P = 0.058 and amblyopic: P = 0.251). However, amblyopes' BPs were dramatically changed at different spatial frequencies (P < 0.001). The amblyopic group consistently showed more negative BP values than the healthy group across all spatial frequencies (0.5 cpd, 2 cpd, and 4 cpd) and interocular orientation differences (9 degrees-90 degrees). Conclusions: Sensory eye dominance is relatively stable across the continuum from binocular combination to rivalry and does not exhibit orientation selectivity in either healthy or amblyopic observers, with greater imbalance shown in the amblyopic group than in the healthy group. These findings highlight a robust but frequency-sensitive imbalance in amblyopic binocular vision.