Delayed effects of the relative humidity on the outpatient visits of dry eye disease in Shanghai, China: effect modification by green and blue space.

Background: Few studies have examined the influence of relative humidity (RH) on dry eye disease (DED), particularly in the context of the urban environment. The objective of this study was to investigate the influence of RH on the frequency of outpatient visits for DED among patients residing in diverse urban settings. Methods: Data pertaining to outpatient visits, together with data on the DED, meteorological factors and air pollutants in Shanghai for the period 2019-2023, were retrieved. To analyse the nonlinear connection and lag impact between RH and outpatient visits for DED patients, a distributed lag nonlinear model (DLNM) was fitted. Results: A total of 159 832 cases were utilised for the investigation. The results of the single-day lag pattern demonstrated a significant correlation between elevated RH exposure and DED. Lower RH was a substantial risk factor for DED on the basis of the cumulative-day effect pattern. Male were more susceptible to DED, and patients aged 0-18 years presented more stable performance in response to RH influences. In the cumulative-day lag pattern, the green space groups, the RR of the >60 years subgroup was greater than that of the other subgroups, and in the blue space groups, the RR of the 19-60 subgroup of blue space Conclusions: Reduced RH increases the relative risk of DED outpatient visits and suggests that a specific disease burden is associated with low RH exposure. Additionally, green and blue spaces in urban areas influence RH, which in turn affects the outpatient visits of DED at different ages.