Association between smoking status and choroidal thickness in the Korean population: Korea National Health and Nutrition Examination Survey 2017–2021

Smoking has been suggested to influence choroidal circulation and structure, but population-based evidence regarding its association with choroidal thickness remains limited. This cross-sectional, population-based study investigated the association between smoking status and subfoveal choroidal thickness (SFCT) in a nationally representative Korean population, using data from the Korea National Health and Nutrition Examination Survey (KNHANES) 2017–2021. A total of 22,130 participants from KNHANES who had gradable optical coherence tomography images and without ocular pathologies affecting choroidal thickness were included. Smoking status was categorized as never, former, and current smoking based on standardized KNHANES questionnaires. Weighted mean SFCT across smoking groups was compared, and association between smoking status and SFCT were estimated using survey-weighted multivariate linear regression. Mean SFCT showed a stepwise increase from never to former to current smokers in both eyes (right eye: 297.3 ± 1.3 µm, 307.0 ± 2.1 µm, and 330.6 ± 2.3 µm, respectively; left eye: 297.2 ± 1.3 µm, 305.5 ± 2.2 µm, and 330.1 ± 2.2 µm, respectively; all p < 0.001). In multivariate analysis, current smoking was associated with thicker SFCT (right eye: β = 17.55 ± 3.45 µm, left eye: β = 20.47 ± 3.40 µm; both p < 0.001). Older age, female sex, longer axial length, greater central macular thickness, and the presence of cardiovascular disease were independently associated with thinner SFCT in both eyes (all p < 0.05). Current smoking was independently associated with greater SFCT, providing large-scale population-based evidence of the association between smoking status and choroidal structural changes.