Quantifying Age-Related Anterior and Posterior Corneal Astigmatism Relationships: Insights for IOL Calculators and Topography-Guided LASIK Protocols

Purpose: To investigate the age-related interactions between anterior corneal astigmatism (ACA) and posterior corneal astigmatism (PCA) and their impact on total corneal astigmatism (TCA) using a high-resolution topographer in a large cohort of patients of all ages. Methods: A retrospective review of 19,317 eyes seeking refractive surgery was conducted. ACA, PCA, and TCA were measured using the Pentacam HR. Corneal data was categorized into astigmatism axes subgroups: with-the-rule (WTR), oblique, and against-the-rule (ATR), and analyzed across ten age groups. ACA, PCA, and TCA (magnitudes and axes), along with Pearson correlation coefficients between ACA and PCA, were calculated for all groups. Correlation between “TCA minus ACA” and selected variables were also assessed. Results: ACA decreased by 37.6% from 18 to 65 years old (yo), followed by a 9.8% increase after 72 yo (P < 0.001). From 18 to 87 yo, PCA consistently decreased by 33.3% with age (P < 0.001). TCA showed a 28% decrease from ages 18 to 59, followed by a 32.3% increase after 72 yo (P < 0.001), which we termed a “V-shaped” trend. In WTR ACA eyes, the correlation between ACA and PCA decreased from R = 0.78 at 18 yo to R ≤ 0.48 in eyes ≥ 65 yo. Oblique ACA eyes showed lower correlations, peaking at R = 0.51 at 24 yo and decreasing to R = 0.02 after 72 yo. ATR ACA eyes showed a mild positive correlation in midlife (R = 0.15; 41 yo), switching to a moderate inverse correlation in older age (R = -0.3461; ≥ 72 yo). Higher ACA magnitude, WTR ACA axis and young age showed strong likelihood of overcorrection if ignoring PCA in laser vision correction (LVC), intraocular lens (IOL), or Phakic IOL (PIOL) refractive treatment (P < 0.0001), whereas lower ACA magnitude, ATR ACA axis and older age were contrarily more likely to undercorrect if ignoring PCA (P<0.0001). Conclusion: The study demonstrates that ACA vs. PCA correlations are highly age-dependent across all orientations. These findings strongly demonstrate that modern IOL calculators should incorporate age-specific correlations to improve TCA prediction accuracy, therefore enhancing patient outcomes in refractive IOL surgery.