Climate Determinants of Keratoconus: Insights From a Systematic Review of Prevalence.

PURPOSE: The reported prevalence of keratoconus varies widely worldwide, but the causes of this variation are not well understood. We therefore aimed to explore the potential impact of local climate variables on keratoconus prevalence.

METHODS

The worldwide prevalence of clinical keratoconus in the general population was systematically reviewed. In each eligible prevalence area, four climate variables deemed possibly relevant to keratoconus were assessed: daily maximum temperature, relative humidity, ultraviolet radiation, and wind speed. Climate variables were calculated using worldwide gridded climate datasets from the European Center of Medium-Range Weather Forecasts. Population density weighting was applied to enhance exposure accuracy. The average of each climate variable was calculated over the 10 years preceding data collection of each study. The potential impact of those climate variables was investigated using multiple linear regression adjusted for the gross domestic product per capita (based on purchasing power parity) with the natural logarithm of prevalence as the outcome variable.

RESULTS

Sixteen eligible studies were identified. After filtering to retain one prevalence estimate per region, 11 studies including datapoints from 61 areas were analyzed. The median (interquartile range) prevalence of keratoconus was 0.10% (0.07%-0.19%). Multiple regression revealed a significant negative association between humidity and keratoconus prevalence (β = -0.03; 95% confidence interval, -0.06 to -0.01; P = 0.004). In contrast, the other analyzed climate variables were not significantly associated with keratoconus prevalence.

CONCLUSIONS

Using global gridded climate maps, we observed a significant and biologically plausible link between low humidity and keratoconus. This suggests that humidification could benefit patients and at-risk groups.