Foveal Crowding and Reduced Binocular Advantage In Myopic Anisometropia Under Brief Stimulus Presentation

To examine whether myopic anisometropia (MA) influences foveal crowding, binocular advantage, and the balance of monocular contributions to binocular vision under brief stimulus presentation. Twenty-two participants were recruited, including 5 with high MA (HMA; mean age 23.20 ± 3.03 years), 9 with low MA (LMA; mean age 24.00 ± 2.78 years), and 8 with non-MA (NMA; mean age 26.88 ± 2.23 years). All participants completed a letter orientation discrimination task under crowded and uncrowded conditions. Sensitivity (D-prime, d’), response time (RT), binocular summation, and the monocular contributions to binocular performance were measured. Foveal crowding was present in all groups under brief stimulus presentation, with no interocular differences within any group. Crowding consistently reduced sensitivity and increased RT across all groups (p < 0.05), while longer presentation durations improved both measures. Notably, the HMA group was the only group that showed no increase in binocular sensitivity relative to monocular at any presentation duration. At 82 ms duration, the LMA group responded more slowly than the NMA group (p < 0.05), while at longer durations (129 ms and 247 ms), the LMA group responded more slowly than the HMA group (p < 0.05). At the shortest duration (47 ms), both MA groups showed a weaker binocular advantage than the NMA group (p < 0.05). Only the NMA group demonstrated a reduction in binocular advantage as presentation time increased (p < 0.05). Further analysis indicated that, while the HMA group maintained a more stable but more unbalanced binocular input contribution. In optically corrected MA patients, brief stimulus presentation revealed abnormal foveal crowding in response time and a reduced binocular advantage, suggesting decreased efficiency in processing visual information under high perceptual demand.