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

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.

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).

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.

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.

Incorporating axial length into OCT normative interpretation may improve clinical assessment of retinal thickness in increasingly myopic populations.