title: Does cigarette smoking alter the risk of pterygium? A systematic review and meta-analysis.
abstract: OBJECTIVE
  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. Meta-regression, 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 = 0.025). The results remained consistent among current smokers (OR, 0.68; 95% CI, 0.61-0.76; P = 4.57 × 10(-12)), but not in ex-smokers (OR, 1.05; 95% CI, 0.87-1.27; P = 0.59). The impact of ultraviolet light (UV) exposure (P = 0.082) and sex (P = 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.
authors.affiliation: Department of Ophthalmology and Visual Sciences, the Chinese University of Hong Kong, Hong Kong, China.
authors.forename: Shi Song
authors.initials: SS
authors.lastname: Rong
authors.affiliation: Department of Ophthalmology and Visual Sciences, the Chinese University of Hong Kong, Hong Kong, China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Peng
authors.affiliation: The Eye Hospital of Wenzhou Medical University, Zhejiang Eye Hospital, Wenzhou, Zhejiang Province, China.
authors.forename: Yuan Bo
authors.initials: YB
authors.lastname: Liang
authors.affiliation: Department of Ophthalmology and Visual Sciences, the Chinese University of Hong Kong, Hong Kong, China.
authors.forename: Di
authors.initials: D
authors.lastname: Cao
authors.affiliation: Department of Ophthalmology and Visual Sciences, the Chinese University of Hong Kong, Hong Kong, China The Shantou University/Chinese University of Hong Kong Joint Shantou International Eye Center, Shantou, Guangdong Province, China Centre for Eye Research Australia, University of Melbourne, Victoria, Australia.
authors.forename: Vishal
authors.initials: V
authors.lastname: Jhanji
mesh_terms: D014943:Global Health; D006801:Humans; D009017:Morbidity; D011379:Prognosis; D011625:Pterygium / Q000453:epidemiology* / Q000209:etiology*; D018570:Risk Assessment; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects* / Q000453:epidemiology
keywords: cigarette smoking; protective factor; pterygia; pterygium; risk factor; smoking