Predictability of different calculators in the minimization of postoperative astigmatism after implantation of a toric intraocular lens

Purpose: To assess the efficacy of five calculators for toric intraocular lenses (IOL). Methods: Retrospective comparative case series in cataract patients undergoing implantation of trifocal toric IOLs (PhysIOL FineVision POD FT). Inclusion criteria were age-related cataract and a corneal astigmatism between 0.90D and 4.50D. Refractive astigmatism predictability of five different toric calculators or calculation methods were compared. Furthermore, two groups were differentiated according to the type of astigmatism. The mean absolute error and the centroid errors in the predicted residual astigmatism from each calculator were evaluated. Results: Fifty-one eyes of 43 patients were included in the study. For the standard toric calculator using anterior keratometry values only, the centroid prediction error was 0.39D +/- 0.41@166 degrees, which was reduced by the application of the PhysIOL toric calculator that includes the Abulafia-Koch regression formula and adjustment for the effective lens position (0.05D +/- 0.34@167 degrees), and also by the application of the Barrett toric calculator (0.07D +/- 0.28@160 degrees). Regarding the techniques that directly evaluate posterior corneal surface, the Holladay toric calculator, using total corneal power provided by a color-LED topographer, generated better results (0.10D +/- 0.44@156 degrees) than those using Scheimpflug camera data (0.23D +/- 0.56@158 degrees). Similar results were found for both types of astigmatism. Conclusion: The PhysIOL and the Barrett toric calculators taking into account the posterior corneal astigmatism by mathematical models, yielded lower astigmatic prediction errors compared to a standard toric calculator based on anterior keratometry data only. When total corneal power measurements were used, prediction errors were lower with color-LED than with Scheimpflug based topography.