U-shaped association between residential greenness and keratoconus

Keratoconus is a blinding corneal disorder influenced by genetic factors. Whether environmental factors influence it remains unclear. Here, we observed a U-shaped association between residential greenness and keratoconus, with increased odds ratios (ORs) at low and high greenness levels. In the Chinese Environment-Ocular Surface (EOS) study, a case-control study of 4341 keratoconus and 3723 controls, the multivariate-adjusted ORs [95% confidence intervals (CIs)] of keratoconus associated with the lowest quartile and the highest quartile of residential greenness were 1.33 (1.23, 1.55) and 1.54 (1.37, 1.72) compared with the intermediate quartile, respectively. In spline analysis, the U-shaped association was consistently indicated, with the lowest odds of keratoconus at the 300 m buffer normalized difference vegetation index (NDVI) of 0.42. Specifically, the association was more pronounced for male, younger (<24 years), and urban-dwelling participants. Urban residents tend to benefit from increased greenness, whereas others may experience adverse effects due to hazards associated with high levels of residential greenness. The association was further validated in a prospective cohort of 502,367 participants from the United Kingdom Biobank (UKB). The results showed that participants with the first quartile residential greenness were 1.8 times (1.12, 2.91) more likely to develop keratoconus than those with intermediate greenness. The results suggested a U-shaped association between residential greenness and keratoconus; both low and high levels of residential greenness were associated with higher odds of keratoconus.