Axial Length–Adjusted Normative Reference Values for Retinal Layer Thickness in a Population-Based OCT Study

Purpose: To establish axial length-adjusted normative reference values for retinal layer thickness using population-based optical coherence tomography (OCT) data and evaluate their clinical implications in highly myopic eyes. Methods: This cross-sectional study used Korea National Health and Nutrition Examination Survey 2017-2021 data. Participants aged ≥19 years with reliable OCT and axial length measurements and without major ophthalmic disease were included. Sampling-weighted quantile regression adjusted for age and sex estimated axial length-specific percentiles for peripapillary retinal nerve fiber layer (RNFL), ganglion cell-inner plexiform layer (GCIPL), and outer retinal thickness, with cluster-bootstrap 95% confidence intervals respecting the survey design. Reference values covered the data-supported range (22-28 mm). RNFL abnormality was reclassified in highly myopic eyes (axial length ≥26.5 mm; sensitivity analysis, ≥26.0 mm). Results: Overall, 10,062 participants were included. Between axial lengths of 22 and 27 mm, median RNFL thickness decreased significantly by 12.4 µm (13.1%; 95% confidence interval [CI], 10.9-13.5; P < 0.001) and GCIPL by 8.2 µm (10.1%; 95% CI, 7.2-9.3; P < 0.001), whereas outer retinal thickness decreased by only 3.2 µm (2.5%). Among 402 highly myopic eyes, the proportion with abnormal average RNFL thickness fell from 16.7% to 4.0% after axial length adjustment (51 of 67 abnormal eyes reclassified as normal), whereas the temporal quadrant showed the opposite pattern. Conclusions: Retinal layer thickness varies substantially according to axial length, particularly in inner retinal layers. Axial length-adjusted normative references may improve OCT interpretation in highly myopic eyes. Translational Relevance: Incorporating axial length into OCT normative interpretation may improve clinical assessment of retinal thickness in increasingly myopic populations.