Astigmatism is a common refractive error affecting how the eye focuses light. Understanding its prevalence involves examining various population studies and how the condition is defined and measured. This provides insight into a frequently encountered aspect of eye health.
Global and National Prevalence
Astigmatism prevalence varies considerably across global populations, ranging from 8% to 62%. A pooled worldwide estimate suggests 40.4% of adults and 14.9% of children have astigmatism.
In the United States, prevalence ranges from 11% to 46%. Data from the 1999-2004 National Health and Nutrition Examination Survey (NHANES) found 36.2% of adults aged 20 or older were affected. Prevalence generally increases with age, with higher rates observed in individuals over 40 and particularly those aged 70 and above. Among children, recent studies note an increase; for example, a Hong Kong report showed prevalence in 6-8 year olds rose from 23.4% before the COVID-19 pandemic to 34.7% in 2022-2023.
Understanding Astigmatism
Astigmatism is an imperfection in the curvature of the eye’s cornea or lens. Normally, the cornea and lens have a uniformly round shape, similar to a basketball. In an eye with astigmatism, this curvature is irregular, often resembling a football.
This irregular shape causes light rays entering the eye to bend unevenly. Instead of focusing sharply onto a single point on the retina, light focuses on multiple points, resulting in blurred or distorted vision. This blurriness can affect vision at all distances, both near and far. Astigmatism can occur in combination with other refractive errors, such as nearsightedness (myopia) or farsightedness (hyperopia).
Factors Influencing Prevalence Data
Reported percentages of astigmatism can differ between studies due to several influencing factors. Age plays a role, as prevalence tends to increase in older populations and can develop or worsen over a lifetime.
Ethnicity also contributes to variations, with some research indicating higher rates in Hispanic and Asian populations compared to Caucasians; China, for example, has reported rates up to 62%. Diagnostic criteria used in studies also impact figures; some define astigmatism at a lower threshold (e.g., 0.5 diopters), while others use a higher one (e.g., 1.0 or 1.5 diopters). Methodological differences in surveys, such as data gathered through self-reporting or clinical examination, study sample size, and geographical location (urban versus rural), further contribute to the observed range in prevalence statistics.