Effects of relative humidity on intraocular pressure using a time-series analysis

This study aimed to investigate the association between ambient humidity and intraocular pressure (IOP), including potential nonlinear relationships and delayed effects of humidity on IOP.

A time-series analysis was conducted using outpatient data collected at Shimane University Hospital between 2018 and 2023. Meteorological data on the days of IOP measurements were obtained from the Japan Meteorological Agency using data from the nearest weather station in Izumo City. Nonlinear relationships between humidity and IOP were evaluated using generalized additive models (GAMs), and delayed cumulative effects of humidity on IOP were assessed using distributed lag nonlinear models (DLNMs).

The dataset included 1,269 observation days and 33,979 IOP measurements, comprising 8,756 measurements over 921 days in the non-glaucoma group and 25,173 measurements over 1,182 days in the glaucoma group. In GAM, nonlinear associations between humidity and IOP were not significant in any group. In the glaucoma group, cumulative exposure to relative humidity of 61-69% and 78-89% over lag 0-6 days, as well as 79-88.5% over lag 0-13 days, was significantly associated with reduced IOP. In contrast, cumulative exposure to very high humidity (97-98%) over lag 0-6 days was significantly associated with increased IOP. No significant cumulative lag effects were observed in the non-glaucoma group.

These findings suggest that short- to middle-term exposure to ambient humidity over the preceding 1-2 weeks may influence IOP in patients with glaucoma.