Keratoconus prevalence in astigmatic adolescents: findings from a nationwide screening setting

Objectives: To assess the association between varying levels of astigmatism and the likelihood of keratoconus diagnosis in adolescents. Methods: This cross-sectional study included 896,377 adolescents aged 16–20 years who underwent a standardised medical assessment between 2011 and 2022, including refraction and topography/tomography in cases where astigmatism above 2.00 dioptres (D) was observed. Astigmatism was categorised into five groups: None, 0.75− < 2.00 D, 2.00– < 3.00 D, 3.00– < 5.00 D, and ≥5.00 D. Logistic regression models were used to assess the association between astigmatism and keratoconus diagnosis. Receiver Operating Characteristic (ROC) curve analysis was performed to evaluate the discriminatory ability of cylinder power in detecting keratoconus. Results: Overall, 1886 adolescents (0.21%) were diagnosed with keratoconus. Increasing astigmatism levels were strongly associated with higher keratoconus prevalence, rising from 0.1% for 0.75– < 2.00 D to 17.4% for ≥5.00 D (p < 0.001). Each 1-diopter increase in cylinder power above 2.00 D was linked to a 1.76-fold increase in keratoconus odds (OR = 1.76, 95% CI: 1.70–1.82, p < 0.001). Astigmatism axis demonstrated limited discriminatory ability. ROC analysis showed moderate discriminatory power for cylinder power (AUC = 0.752), with a cut-off of 2.88 D yielding a sensitivity of 0.744 and a specificity of 0.644. Conclusions: In this large cohort of adolescents, increasing astigmatism power was significantly associated with keratoconus diagnosis. These findings suggest that combining astigmatism thresholds with other clinical factors may enhance screening strategies, enabling timely intervention to prevent disease progression.