Associations of High Myopia and Glucose Metabolism with Subfoveal Choroidal Thickness: A Nationwide Population-Based Study

Purpose To investigate the independent and interactive associations of high myopia (HM) and glucose metabolism status with subfoveal choroidal thickness (SFCT) in a nationwide, population-based study.Methods This cross-sectional study analyzed data from the Korea National Health and Nutrition Examination Survey 2019–2021. Participants were classified into a HM group (axial length [AL] >26.0 mm) and a control group (AL < 24.5 mm). Glucose metabolism status was categorized as normal, prediabetes, or diabetes mellitus (DM). Survey-weighted linear regression analyses were performed to identify independent determinants of SFCT. Interaction terms between HM and glucose metabolism status were additionally included to assess potential synergistic effects.Results A total of 9,132 participants were included, of whom 1,118 (12.2%) were classified as HM. The distribution of glucose metabolism status differed significantly across groups (p < 0.001), with a higher prevalence of prediabetes and DM in the control group (46.4% vs. 34.3% and 15.4% vs. 10.1%, respectively). HM was associated with a substantial decrease in SFCT (β = −107.25, p < 0.001), whereas prediabetes was associated with an increase in SFCT (β = 5.58, p = 0.015) after full adjustment for potential confounders. DM showed no significant association with SFCT (p = 0.705). No significant interaction was observed between HM and glucose metabolism status, indicating additive rather than synergistic effects. These findings were consistent across sensitivity analyses.Conclusion In this nationwide, population-based study, prediabetes was associated with increased SFCT independent of HM. The absence of an association between DM and SFCT suggests that DM may exert opposing, stage-dependent effects on SFCT according to disease severity.