Cigarette Smoking and Pterygium: A Propensity Score Matching Analysis

To assess the association between smoking and pterygium among elderly adults by applying a propensity score matching (PSM) approach and to examine a potential dose-response relationship.

The study was designed as a community-based cross-sectional study based on a Chinese cohort aged 60 years or older in China. Anterior segment examination was performed without pupil dilation using a slitlamp. Pterygium was defined as a raised fleshy triangular fibrovascular tissue growth of the conjunctiva encroaching onto the clear cornea. Information regarding smoking history was collected via a structured interviewer-administered questionnaire. The propensity scores for myopia were formulated using seven potential confounders. We matched the propensity scores for smokers and nonsmokers within a caliper of 0.01 of logit function of propensity scores.

Slitlamp examination was successfully performed in 4567 adults. The odds ratio of pterygium for cigarette smoking before matching was 0.65 (95% confidence interval, 0.56 to 0.75; p < 0.001). There were significant covariate imbalances between comparison groups, and after PSM, covariate imbalances were significantly reduced. After PSM, the magnitude of association was slightly reduced (odds ratio, 0.70; 95% confidence interval, 0.55 to 0.89; p = 0.004). Adults with more daily cigarette consumption were less likely to be affected by pterygium in multivariate analysis (p for trend = 0.02).

Smokers were less likely to be affected by pterygium. The PSM approach may be a useful method to address selection bias in observational studies when randomized trials cannot ethically be conducted.