Cataract in outdoor workers: a systematic review with meta-analysis

Ultraviolet B radiation (UVB) from sunlight is an established risk factor of cataract which is a leading cause of vision loss worldwide. This review evaluates the epidemiological evidence on the association between cataract and working outdoors. We conducted a systematic literature search to identify studies providing quantitative age- and sex-adjusted estimates of the association between working outdoors and risk of cataract. Random effects meta-analysis across studies was stratified by study design and type of cataract. Evidence synthesis was based upon evaluation of bias and confounding. We identified ten case-control, and seven eligible cross-sectional studies published from 1985 to 2016. The two most informative studies included large populations, individual estimates of cumulative lifetime UVB exposure, and comprehensive eye examinations. Both studies reported strong associations between outdoor work and cataract (OR 2–3) but included only occupational groups with exceptionally high levels of sunlight exposure. The meta-analysis also including a number of studies with methodological limitations showed a weighted average odds ratio of 1.43 (95% CI: 1.12–1.83) for non-specific cataract among sunlight exposed workers, with significant heterogeneity between studies (Q = 54.8, p < 0.001) reflecting different study designs, exposure levels and reference groups. There is strong evidence that cumulative lifetime UVB radiation exposure from sunlight increases the risk of cataract, and that outdoor work contributes to this risk. However, the available evidence is inadequate to quantify the relative impact of occupational sunlight exposure versus other sources across occupations, geographic regions, and seasons.