Epidemiology of Astigmatism in Japan: Analysis of More Than 9,000,000 Spectacle Prescriptions

Purpose: The purpose of this study was to characterize the prevalence of astigmatism and stratify it by age, sex, and geographic region and evaluate interocular differences in cylinder power in a large-scale Japanese population using spectacle prescription data. Methods: This retrospective cross-sectional study analyzed de-identified spectacle prescription data collected from a nationwide optical retail chain between September 2021 and August 2023. The targeted individuals were aged 6 to 89 years. They were categorized based on their cylinder power and axis orientation. Step 1 involved evaluating these parameters across different ages, sexes, and regions. Step 2 involved quantifying the interocular differences in the individuals with astigmatism (cylinder power of ≥0.25 diopter [D]) in at least one eye. Results: We analyzed 9,204,993 prescriptions (50.8% female subjects). The cylinder power increased progressively with age, and this was accompanied by a shift from with-the-rule (WTR) to against-the-rule (ATR) orientation. Men had slightly higher cylinder powers and a higher prevalence of ATR astigmatism than women. The regional variation across Japan was modest. Interocular comparison revealed that 81.6% and 9.4% of the individuals had differences in cylinder power of ≤0.50 D and ≥1.00 D, respectively. These findings indicate substantial bilateral symmetry in most individuals. Conclusions: This nationwide analysis of spectacle prescription data provides an updated epidemiologic overview of astigmatism in Japan. We characterized the age-, sex-, and region-related variations in cylinder power and axis orientation and quantified the interocular asymmetry at the population level. These findings highlight the value of large-scale prescription databases as a novel resource for population-based vision research.