Interocular symmetry and biometric correlates of parafoveal cone mosaic metrics in adolescents: a cross-sectional adaptive optics study

Aims To characterise the cone mosaic in adolescents using adaptive optics scanning laser ophthalmoscope and to investigate the inter-ocular symmetry and biometric determinants of cone metrics and their functional significance. Methods This cross-sectional study enrolled adolescents aged 15–18 years without ocular pathology. Adaptive optics imaging was performed to quantify cone density, spacing and regularity at 3° temporal to the fovea. Measurement reproducibility and interocular symmetry were evaluated through paired comparisons and absolute discrepancy analysis. Linear mixed models identified independent ocular determinants of cone metrics and their associations with visual acuity. Results Adaptive optics showed excellent reproducibility for cone density and regularity. Mean cone density was 13 647 cells/mm² in dominant eyes at 3° temporal, with no significant interocular differences in any cone metric. Absolute interocular discrepancy was greater for cone density (16.96%) than regularity (1.59%) or axial length (1.48%; both p<0.001). Directional interocular difference in axial length was independently associated with differences in angular density (β=0.48, p=0.045) and regularity (β=0.52, p=0.025). Axial length and retinal thickness independently determined physical spacing. Cone regularity showed the most consistent association with best-corrected visual acuity (b = −0.0089, p=0.024). Conclusions Adolescent parafoveal cone mosaics show close group-level interocular symmetry, while directional asymmetry in the angular mosaic tracks differences in axial elongation between dominant and non-dominant eyes. Axial length and retinal thickness independently associate with cone spacing. Topological regularity appears to be the structural correlate of visual function in adolescents.