Astigmatism is a common eye condition that affects how the eye focuses light, often resulting in blurred or distorted vision. This refractive error occurs because the cornea or lens, instead of being perfectly spherical like a baseball, is curved more irregularly, resembling the shape of a football. This unequal curvature causes light to focus at multiple points instead of a single point on the retina. It is one of the most frequently diagnosed vision problems worldwide.
Defining the Prevalence Measurement Threshold
Determining the exact percentage of people with astigmatism is complicated because the reported prevalence figures depend entirely on the measurement threshold used in a study. Ophthalmic science quantifies the severity of astigmatism using a unit called a diopter (D), which measures the difference in curvature between the eye’s steepest and flattest meridians. A higher diopter value indicates a greater degree of irregularity in the eye’s shape.
Many large-scale population studies choose a cylinder power of \(\geq 0.5\) D as the cutoff for defining astigmatism. This relatively low threshold captures very mild cases that may not require correction or cause noticeable symptoms. Studies using this definition will naturally report a much higher prevalence rate.
A more clinically significant threshold often used in research is \(\geq 1.0\) D, which typically represents a level of astigmatism that warrants corrective lenses. When this stricter standard is applied, the reported prevalence drops considerably, illustrating why different studies offer such varied statistics. The answer to “what percent” is not a single number but depends on the level of severity considered.
Global and Regional Prevalence Statistics
Astigmatism is widely considered the most common refractive error globally, with prevalence estimates varying significantly based on the population studied and the diagnostic cutoff used. Across the general population, the overall rate of astigmatism has been reported to range from 8% to 62%. When a moderately strict definition is applied, the estimated pooled prevalence in adults worldwide is approximately 40.4%.
Prevalence rates differ noticeably when comparing age groups, with children generally showing a lower rate than adults. The estimated pooled prevalence for astigmatism in children is around 14.9% globally. However, specific studies using the \(\geq 0.5\) D threshold in school-aged children still report higher figures, such as 28.4% in one American study.
Significant regional and ethnic variations exist, indicating that astigmatism is not uniformly distributed. Studies have found particularly high rates in certain South-East Asian populations, where the condition is often the most prevalent refractive error among adults. Data from China have reported some of the highest prevalence figures, reaching up to 62% in certain cohorts. In contrast, rates in Northern and Western Europe have been reported around 27%, while figures in the United States show a broad range from 11% to 46%.
Key Demographic Factors Influencing Rates
Several demographic factors are statistically linked to a higher likelihood of having astigmatism, providing context for the varying prevalence statistics.
Age
Age is a major determinant, as the prevalence of astigmatism tends to increase throughout adulthood, particularly after the age of 40. This increase is often dramatic in older cohorts, with rates climbing up to 67.2% in individuals over 65 years old in some rural populations.
The physical characteristics of astigmatism often change as a person ages, shifting from with-the-rule astigmatism to against-the-rule astigmatism. This shift is thought to be related to changes in the tension of the eyelids and the lens inside the eye over time.
Ethnicity and Geography
Ethnicity and geographic origin also play a role, with studies consistently showing differences across population groups. Research in the United States has found that children of Hispanic and African-American descent are statistically more likely to have astigmatism compared to non-Hispanic white children.
Genetics
Genetic factors contribute substantially to an individual’s risk, suggesting a hereditary component. Studies on families have shown that children who have astigmatic parents face a significantly greater risk—approximately two times higher—of developing the condition themselves. A family history of astigmatism is one of the most reliable predictors of its presence.