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 μg/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 NO(2), 1.0089 (1.0030–1.0149) for O(3), 1.0004 (0.9976–1.0032) for PM(2.5), 1.0033 (0.9982–1.0083) for PM(10), and 1.0045 (0.9908–1.0185) for SO(2). In the subgroup, PM(2.5) 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 PM(2.5), NO(2), and O(3). Reductions of air pollution levels are still warranted to protect the vulnerable populations.