Protective effect of smoking against pterygium development in men: a nationwide longitudinal cohort study in South Korea

OBJECTIVE The present study aimed to evaluate the association between smoking and incident pterygium in adult Korean men. DESIGN A retrospective nationwide longitudinal cohort. SETTING National Health Insurance database of South Korea. PARTICIPANTS This study included Korean men (age range: 40-79 years) registered in the Korea National Health Insurance Service database from 2002 through 2013. We compared HRs for pterygium between 90 547 current/past and 90 547 never-smokers via 1:1 propensity-matched analysis. PRIMARY OUTCOME MEASURE Incident cases of pterygium were identified from the database. RESULTS Pterygium developed in 5389 (6.0%) never-smokers and 3898 (4.3%) past/current smokers (P<0.001). The incidence of pterygium per 1000 person-years in never-smokers and in past/current smokers was 6.5 and 4.7, respectively (age-adjusted HR, 0.73; 95% CI, 0.70 to 0.76). This protective effect was more pronounced among current smokers than among past smokers (for current smokers: HR, 0.68; 95% CI, 0.65 to 0.71 and for past smokers: HR, 0.85; 95% CI, 0.80 to 0.90). A longer duration of smoking and higher amounts of cigarette consumption were associated with a lower incidence of pterygium. CONCLUSIONS Longitudinally, cigarette smoking was associated with a reduced risk of pterygium, and this protective effect was more pronounced among current smokers than among past smokers.