1. Cigarette smoking was associated with a decreased the risk of pterygium.
2. UV-exposure and gender, well-known risk factors for pterygium, were not found to be confounders in this analysis.
Evidence Rating Level: 1 (Excellent)
Study Rundown: Pterygium is a non-cancerous growth on the inner portion of the eye and may reduce visual acuity. Previously determined risk factors include UV exposure, male gender, and older age. Smoking has been previously investigated as a potential risk factor with contradictory results. In this particular report, the authors conducted a systematic review of over 20 studies to determine the effect of smoking on pterygium. Reviewing data for almost 100,000 patients, the authors found that cigarette smoking significantly decreased the risk of developing pterygium. Furthermore, when the group was split into current and former smokers, only current smokers retained the protective effect. The authors ensured that gender and UV exposure did not affect the analysis of smoking. Limitations include the lack of metrics used to gauge UV exposure (e.g., outdoor work, use of sunglasses) and the limited variety of different studies. The study also did not stratify smokers by the length or intensity of smoking. These findings suggest that there may be a molecular basis to the protective effect of smoking, which could be therapeutically valuable if isolated from the harmful aspects of smoking.
Relevant Reading: Pterygium: are we any closer to the cause?
In-Depth [meta-analysis]: This meta-analysis included 24 different studies (case-control, cross-sectional, and cohort) involving over 95,000 pterygium patients. Publications that confirmed diagnosis of pterygium, smoking status, and contained odds ratio (OR) calculations were identified. Smoking status was classified as never smoked, ex-smokers, and current smokers. Meta-analyses were used to calculate overall ORs. Exposure to smoking was shown to have a protective effect, with an OR of 0.82 (95% CI 0.69-0.97, p=0.025). When the group was split into ex-smokers and current smokers, the effect remained with current smokers (OR 0.68; 95% CI 0.61-0.76, p<0.001) but not ex-smokers (OR 1.05; 95% CI 0.87-1.27, p=0.59). Meta-regression showed that UV exposure and gender did not confound the effect of smoking on pterygium (p= 0.082, 0.553 respectively.) The protective association of smoking on pterygium was preserved in Asian (OR 0.66; 95% CI 0.58-0.76, p=1.69×10-9) or Caucasian ancestry (OR 0.77; 95% CI 0.62-0.97, p=0.024)
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