Comparison of Total Corneal Tomographic Astigmatism with Predicted and OCT Measured Posterior Corneal Astigmatism in Toric IOL Calculations

Accurate calculation of toric intraocular lenses (IOLs) remains challenging, particularly in accounting for posterior corneal astigmatism. This study compared the prediction accuracy of two industry-standard toric calculators using ray-traced total corneal astigmatism (TCA). In a two-year retrospective chart review at an academic outpatient center, patients undergoing femtosecond laser-assisted cataract surgery with toric IOL implantation were included, excluding those with corneal pathology, irregular astigmatism, prior ocular surgery, or maculopathy. Tomographic and ray-traced TCA along with swept-source OCT (SS-OCT) biometry were entered into the Tecnis Toric Calculator (TTC), while SS-OCT values were entered into the Barrett Toric Calculator (BTC) using both predicted posterior corneal astigmatism (P) and measured posterior corneal astigmatism (M). Absolute prediction errors (PE) of spherical equivalent and cylinder power were compared, with subgroup analysis of with-the-rule (WTR) and against-the-rule (ATR) astigmatism. Sixty eyes of forty patients were analyzed. TTC with TCA achieved lower mean absolute cylinder PE (0.52 D) than BTC with P (0.59 D, p=0.016) and M (0.56 D, p=0.024), with significant advantages in WTR eyes but not ATR eyes. Across calculators, ATR eyes showed greater residual error and overcorrection. These findings support incorporating ray tracing and tomography to improve toric IOL prediction accuracy.