Ocular dominance is associated with interocular asymmetry in refractive error and axial length across childhood and early adulthood

Purpose: To determine whether ocular dominance is associated with systematic interocular asymmetry in spherical equivalent refraction (SER) and axial length (AL) across childhood and early adulthood, and assess whether such asymmetry exceeds laterality effects. Methods Data were analysed from three population-based cohorts: 728 children (6-7-year-olds), 898 adolescents (12-13-year-olds) from Ireland, and 303 young adults (25-30-year-olds) from Western Australia. Ocular dominance was assessed using sighting tests. SER was measured by cycloplegic autorefraction, and AL by optical biometry. Interocular differences were evaluated using paired comparisons, concordance correlation coefficients, Deming regression, Bland–Altman analyses, and mediation modelling. Analyses were stratified by refractive status and anisometropia. Results Across all age groups, right–left differences in SER and AL were minimal (mean differences <0.05D and <0.05mm in children and adolescents), with small, significant laterality effects observed only in young adults (−0.13D in SER; 0.06mm in AL). In contrast, dominant–non-dominant comparisons demonstrated consistent directional asymmetry: the dominant eye was less hyperopic/more myopic (−0.09D at 6–7 years; −0.10D at 12–13 years; −0.20D at 25–30 years) and longer (0.03–0.07mm; all p<0.05). Deming regression and Bland–Altman analyses confirmed systematic deviation from interocular symmetry, most pronounced in childhood. Mediation analyses indicated that ocular dominance statistically explained over 85% of the observed interocular asymmetry, independent of laterality. Dominance-related asymmetry was most evident in non-myopes (SER −0.09 to −0.36D; AL 0.03–0.06mm), attenuated in myopia, and amplified in anisometropia (SER up to −1.09D; AL up to 0.42mm), particularly in younger cohorts. Conclusion In this cross-sectional analysis, ocular dominance was associated with small but systematic interocular asymmetry in SER and AL across childhood and early adulthood, which exceeds laterality effects. Dominance-related asymmetry was attenuated in myopia and amplified in anisometropia. Ocular dominance should be considered when analysing interocular refractive and biometric data in research and clinical contexts.