PURPOSE. To determine the association of cigarette smoking with pterygium. METHODS. Potentially eligible studies published from the year 1946 to December 28, 2013 were identified from MEDLINE, EMBASE, and Cochrane Library databases, and reference lists. All studies that evaluated smoking as an independent factor for pterygium were identified. Study-specific odds ratios (ORs) were combined using the random-effects model when P < 0.1 in the test for heterogeneity, or otherwise the fixed-effects model was used. Metaregression, sensitivity analysis, and evaluation of potential biases were undertaken. The ORs with 95% confidence intervals (CIs) of smoking as an associated factor for pterygium were analyzed. RESULTS. We included 24 articles incorporating 95,279 participants from 20 cross-sectional studies, 2 hospital-based case-control studies, and 2 population-based cohort studies. The combined OR of cigarette smoking (current or ever smoked) for risk of pterygium was 0.82 (95% CI, 0.69-0.97; P ¼ 0.025). The results remained consistent among current smokers (OR, 0.68; 95% CI, 0.61-0.76; P ¼ 4.57 3 10 À12 ), but not in ex-smokers (OR, 1.05; 95% CI, 0.87-1.27; P ¼ 0.59). The impact of ultraviolet light (UV) exposure (P ¼ 0.082) and sex (P ¼ 0.553) on the effect of smoking was insignificant in meta-regression. Sensitivity analysis confirmed the protective effect and nonrelevance of these two study-level variables. Begg's funnel plots and Egger's test showed minimal publication bias. CONCLUSIONS. The results of this meta-analysis show that cigarette smoking was associated with a reduced risk of pterygium, especially in current smokers. This effect may be independent of UV exposure and sex. Investigations are needed to unveil its molecular basis serving therapeutic purposes. Keywords: smoking, cigarette smoking, pterygium, pterygia, risk factor, protective factor P terygium is an inflammatory fibrovascular mass that extends from the interpalpebral conjunctiva over the adjacent peripheral cornea. 1 Its corneal ingrowth can lead to ocular irritation and visual impairment by induction of astigmatism, blockade of visual axis, or loss of corneal transparency. 3-24 Cigarette smoking, a modifiable factor and an important public health problem, has been studied as a risk factor for pterygium. METHODS Eligibility Criteria We included studies that fulfilled the following criteria: (1) a cross-sectional, prospective cohort, or case-control study; (2) diagnosis of pterygium was based on slit-lamp examination by ophthalmologists; (3) smoking status was recorded and tested as an independent factor; (4) adjusted odds ratio (OR) and 95% confidence interval (95% CI) were estimated with multiple logistic regression; or the occurrence of pterygium in subjects with and without current/past smoking history were reported or can be resolved. Animal studies, case reports, reviews, abstracts, conference proceedings, editorials, non-English articles, and studies that did not analyze smoking as a factor were excluded
