Astigmatism trends in adults of Hong Kong from 2015 to 2024: The Hong Kong Children Eye Study

To investigate temporal trends in refractive and corneal astigmatism (CA) in adults and examine their association with the COVID-19 pandemic.

This population-based cross-sectional study included adults (≥18 years) recruited from parents participating in the Hong Kong Children's Eye Study who underwent comprehensive ocular examinations at two academic centres (2015-2024). Refractive error of the worse eye and corresponding CA were measured using an autorefractor and optical biometry without cycloplegia. Age-standardised prevalence was calculated annually. Logistic regression assessed associations between the pandemic period and astigmatism, adjusting for age, sex, axial length and spherical equivalent.

A total of 29 583 adults (mean age 40.6±5.6 years; 35.3% men) were included. Age-standardised prevalence of refractive astigmatism (RA) increased from 41.7% in 2015 to 46.2% in 2024 (p=0.002) and CA from 45.0% to 52.9% (p=0.002). Compared with 2015, the adjusted odds of RA in 2024 increased by 52% (OR 1.52, 95% CI 1.30 to 1.76; p=9.34×10^-8), and CA by 47% (OR 1.47, 95% CI 1.27 to 1.71; p=2.38×10^-7). Mean refractive and CA increased by 0.11 D and 0.14 D, respectively. A shift towards moderate and severe astigmatism was observed. CA correlated strongly with K2 (β=0.891, p<0.001).

The prevalence and severity of astigmatism in adults increased following the COVID-19 pandemic, independent of axial length and spherical equivalent. Findings suggest corneal changes, especially along the steep meridian, may underlie this trend and warrant further investigation into environmental and lifestyle factors.