Predictability of Residual Postoperative Astigmatism After Implantation of a Toric Intraocular Lens Using Two Different Calculators

Purpose: To compare predictability of postoperative refractive astigmatism (RA) using the Emmetropic Verifying Optical (EVO) Toric Formula v2.0 to one that accounts only for anterior corneal astigmatism. Methods: This is a secondary analysis of de-identified data from a clinical trial including 9 sites across the United States. Preoperative biometry was used to predict postoperative RA with the implanted toric IOL using legacy enVista and EVO online calculators. The RA prediction error was computed between back-calculated postoperative RA and predicted residual RA. Outcome measures included vector (centroid) and arithmetic mean RA prediction error. Results: Comparison of calculators was based on 109 eyes, 97 (89%) of which were implanted with a toric IOL with an effective astigmatism power of 1.4 D or less. Centroid of the RA prediction errors was 0.37 D @ 178 and 0.17 D @ 090 for the legacy and EVO calculators, respectively (p < 0.0001). The proportion of eyes with an absolute RA prediction error <= 0.5 was 47.3% and 49.1% (p = 0.78), while the proportion of eyes <= 1.0 D was 82.7% and 89.1% (p = 0.03). Differences in the proportions <= 0.5 D existed for WTR (p = 0.015) but not ATR (p = 0.75) eyes. The proportion in which orientation of the predicted RA (ATR, WTR, or oblique) matched the actual RA was 62% and 78% for legacy and EVO calculators, respectively (p = 0.0029). Conclusion: The EVO Toric Formula v2.0 out-performed the legacy calculator with regards to predictions in eyes with low astigmatism.