To study astigmatism and astigmatism rule by 1) determining changes in prevalence in the United States between 1971-1975 and 1999-2008 and 2) identifying associations with demographic factors.
National survey.
Retrospective cross-sectional study.
Participants of the 1971-1975 and 1999-2008 National Health and Nutrition Examination Survey (NHANES) aged 20-74 years representing the United States population. The 1971-1975 NHANES measured astigmatism in individuals using an algorithm based on presenting visual acuity, lensometry and objective refraction. We implemented similar methods using 1999-2008 NHANES data for comparison. We identified prevalence of clinically significant astigmatism (≥1.0 D) and used logistic regression models to assess demographic associations with rule of astigmatism.
Main outcomes were prevalence estimates of astigmatism and odds ratios estimating associations with demographic characteristics. There was an increase in astigmatism from the 1970’s to 2000’s [14% (95% CI: 13.2-14.5) vs. 24% (22.8-24.6)], which was more pronounced in men [12% (10.8-12.7) vs. 23% (21.9-24.2)] than women [16% (14.9-16.8) vs. 24% (23.0-25.7)]. In adjusted analysis of the 2000’s cohort, myopes had 8.34 (CI: 7.30-9.54) times greater odds of astigmatism than non-myopes. In the 2000’s, there was increased odds of ATR astigmatism in males (OR, 1.4; 95% CI: 1.1-1.8) compared to females, non-myopes (OR, 2.3; 95% CI: 1.7-3.1) compared to myopes, and 60-74 year olds (OR, 3.7; 95% CI: 2.7-5.1) compared to 20-39 year olds.
There is greater prevalence of astigmatism and against-the-rule astigmatism in 1999-2008 compared to 30 years prior. Factors associated with against-the-rule astigmatism were being male, white, and nonmyopic.

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