Global Associations of Air Pollution and Conjunctivitis Diseases: A Systematic Review and Meta-Analysis

(1) Background: As the most common eye disease diagnosed in emergency departments, conjunctivitis has caused serious health and economic burdens worldwide. However, whether air pollution may be a risk factor for conjunctivitis is still inconsistent among current evidence. (2) Methods: We searched the literature on the relationship between air pollution and conjunctivitis in multiple English databases before 18 March 2019. Meta-analysis, meta-regression, and funnel plots were used to integrate the data, identify the sources of bias, and determine the publication bias, respectively. (3) Results: A total of 2450 papers were found, 12 of which were finally included. The pooled relative risk for each 10 mu g/m(3) increase of air pollution on conjunctivitis was 1.0006 (95%CI: 0.9993-1.0019) for CO, 1.0287 (1.0120-1.0457) for NO2, 1.0089 (1.0030-1.0149) for O-3, 1.0004 (0.9976-1.0032) for PM2.5, 1.0033 (0.9982-1.0083) for PM10, and 1.0045 (0.9908-1.0185) for SO2. In the subgroup, PM2.5 and O-3 had a greater impact on conjunctivitis risk in women than in men, and people <18 years old than those >= 18 years old. Relative humidity significantly modified the risk of O-3 on conjunctivitis (p = 0.023), explaining 45% of the between-study heterogeneity. (4) Conclusion: Globally, air pollution has considerable health risks for conjunctivitis. Females and the youth were more vulnerable to PM2.5, NO2, and O-3. Reductions of air pollution levels are still warranted to protect the vulnerable populations.