Age-Related Variations in Anterior, Posterior, and Total Corneal Astigmatism

Toric intraocular lens (IOL) calculation has traditionally relied on anterior corneal astigmatism (KA), but recent trends emphasize incorporating posterior corneal astigmatism (PCA) and total corneal astigmatism (TCA). However, age-related changes and sex-based differences in PCA and TCA remain inconclusive due to limited sample sizes in previous studies.

We conducted a cross-sectional observational study using biometric measurements obtained with the IOLMaster 700. Patients with warning and failed history of corneal transplant or keratoconus were excluded. The objective was to evaluate age-related changes and sex-based differences in KA, PCA, and TCA among patients undergoing cataract surgery at a tertiary care center in Thailand.

A total of 23,932 eyes were analyzed for KA, and 9,546 eyes for PCA and TCA. Data were visualized using double-angle plots. PCA demonstrated a distinctive three-point star distribution, predominantly oriented along the with-the-rule (WTR) axis, with against-the-rule (ATR) astigmatism being rare in younger patients as illustrated in graphical abstract. Across KA, PCA, and TCA, the prevalence of ATR astigmatism increased in older age group, while WTR orientation decreased. A marked shift from WTR to ATR orientation was observed at different age thresholds: 60-65 years for KA, 75-80 years for PCA, and 55-65 years for TCA. KA and TCA also exhibited a preferential shift toward superonasal oblique orientation with advancing age-a pattern not observed in PCA. No significant sex-based differences were observed in mean astigmatism vector distributions across age groups.

Clinicians should account for age-related shifts in KA, PCA, and TCA when selecting toric IOLs, particularly in patients younger than 55 years. Preoperative counseling should address potential long-term shifts toward ATR orientation, which may influence visual outcomes in patients receiving toric IOLs aligned along other axes. Incorporating these changes into toric IOL formulae may improve patient outcomes.