Global Patterns of Myopia, Age, Sex, and Vision Loss: A Comparative Analysis of US and South Korean National Surveys

Objective Myopia prevalence is rising globally and has reached critical levels in some regions. Beyond refractive correction needs, myopia is a major risk factor for irreversible, vision-threatening ocular disease. This study investigated the relationship between myopia, age, sex, and visual impairment in two nationally representative populations in the United States and South Korea. Design Cross-sectional analysis using data from the U.S. National Health and Nutrition Examination Survey (NHANES) and the Korean National Health and Nutrition Examination Survey (KNHANES). Participants Participants in the NHANES and KNHANES. Methods Best-corrected visual acuity and non-cycloplegic refractive error were analyzed from NHANES (1999–2008) and KNHANES (2008–2022), excluding those with cataract or refractive surgery. Visual impairment was defined as best-corrected visual acuity ≥0.30 LogMAR. Logistic regression and Kaplan–Meier analyses were used to evaluate and visualize the cumulative risk of visual impairment by refractive error age and sex. Main Outcome Measure Visual impairment probability and the Odds Ratios for visual impairment by region, age and degree of myopia. Results Visual impairment rates increased with both myopia severity and age in both populations. Among younger non-myopes, impairment affected 1%, rising to 50% in high myopes by age 75. High myopes had up to 13-fold higher odds of visual impairment than non-myopes. Age-related risks were similar across regions, but myopia had a stronger effect in South Korea: each 1 D increase in myopia raised the odds of impairment by 41% versus 27% in the USA. Sex was not a significant factor in the U.S. (p = 0.207) but was significant in South Korea (OR: 1.69, 95% CI: 1.33–2.14, p < 0.01). Conclusions Myopia substantially increases the risk of visual impairment in both the United States and South Korea, with risk rising proportionally with myopia severity. Age-related effects were similar across cohorts, though myopia exerted a greater influence in South Korea. Females demonstrated higher rates of visual impairment independently of refractive error. These findings highlight myopia as a global health concern, reinforcing the need for prevention and early intervention to reduce lifetime risk across all severities.