Prevalence and Distribution of Axis Subtypes of Refractive Astigmatism in Mexican Outpatients: A Nationwide Multicenter Clinic-Based Cross-Sectional Study.

Background/

Objectives

Astigmatism is one of the most common refractive errors and represents a risk factor for other ocular conditions, including myopia and amblyopia. In Mexico, comprehensive epidemiological data on refractive astigmatism, particularly its axis-related subtypes, remain limited. This study aimed to estimate the prevalence and distribution of axis subtypes of refractive astigmatism in a nationwide, clinic-based cohort of Mexican outpatients.

Methods

We conducted a retrospective, cross-sectional, multicenter study using anonymized electronic health records (EHRs) from Salud Digna clinics across all 32 states of Mexico. Individuals aged 5-90 years who underwent routine non-cycloplegic eye examinations between 2021 and 2023 were included. Refractive astigmatism was defined as a cylinder power (Cyl) of ≤-0.75 D. Age-adjusted prevalence and distribution of axis subtypes (with-the-rule [WTR], against-the-rule [ATR], and oblique [OBL]) were determined according to sex, age groups, and geographic locations. Logistic regression models evaluated potential associations between demographic variables and refractive astigmatism.

Results

Data from 8,622,191 individuals were analyzed (median age: 45 years; 63.4% females). The age-standardized prevalence of refractive astigmatism was 41.59% (95% CI: 41.54-41.64%) and was higher in males (45.43%) than females (39.32%). WTR astigmatism predominated among younger individuals, peaking at ages 15-19 (48.97%), whereas ATR astigmatism increased with age, reaching 35.36% among those aged 80-90 years. In multivariable analysis, refractive astigmatism was significantly associated with age, sex, and state of residence, showing a non-linear, non-monotonic age pattern with peaks in adolescence (aOR = 1.47; 95% CI, 1.456-1.484) and older (aOR = 1.177; 95% CI, 1.161-1.193) age, higher odds in males (aOR = 1.269; 95% CI, 1.265-1.272), and marked geographic variability, with the highest in Tlaxcala (aOR = 3.581; 95% CI, 3.491-3.675).

Conclusions

Refractive astigmatism was more prevalent in males and showed a clear age-related shift in the axis subtype beginning in the early 40s. These findings provide large-scale, real-world evidence that enhances the understanding of astigmatism epidemiology in Mexico and may inform future research and public health planning.