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Cataract surgery has become a refractive procedure after which patients expect to achieve excellent uncorrected postoperative visual outcomes. Toric intraocular lenses (IOLs) have been shown to be effective in correcting corneal astigmatism.1–3 The success of toric IOLs depends on accurate estimation of the total corneal astigmatism and accurate calculation of the required toric IOL.3,4 Originally, toric IOL calculations relied solely on anterior corneal measurements, assuming a fixed anterior-posterior curvature ratio.5 Results of several studies have indicated that incorporating posterior corneal astigmatism (PCA) into the toric IOL calculation improves the refractive outcomes.5–12 Direct measurement of the posterior corneal curvature is now possible with new technologies, such as Scheimpflug and optical coherence tomography devices. Unfortunately, these devices are not always available in clinical practice. One possible solution is to use adjustment methods that consider the PCA power and axis. The Abulafia-Koch formula, described by Abulafia et al,13 is a regression formula that calculates an estimated net corneal astigmatism using standard keratometry measurements. The Barrett toric calculator uses a mathematical prediction method of PCA based on the Barrett Universal II formula together with consideration of the anterior and the posterior corneal curvatures (https://ascrs.org/tools/barrett-toric-calculator).11 Both methods have been found to yield comparable or even better results than calculations incorporating direct PCA measurements.14–16 However, predicted values can be inaccurate in extreme cases, such as very high PCA. Our study aimed to evaluate the prediction error of toric IOL calculations in a subgroup of cases of PCA of 0.80 diopters (D) or greater using methods that predict the PCA and to compare the results to calculations using direct PCA measurements.
Patients and Methods
This study involved a retrospective review of consecutive medical records of patients who had cataract surgery with implantation of toric IOLs whose PCA was 0.80 D or greater. The surgeries were performed by a single surgeon (GK) at Ein-Tal Eye Center, Tel Aviv, Israel, from July 2012 to July 2019. The institutional ethics committee of the Meir Medical Center, Kfar-Saba, Israel, approved this study.
Inclusion criteria included: implantation of a toric IOL, preoperative biometric measurements and dual-zone autokeratometry by the Lenstar device (Lenstar LS900; Haag-Streit AG), measurements of PCA with the Scheimpflug camera (Pentacam; Oculus Optikgeräte GmbH) graded by the instrument as “OK,” postoperative manifest refraction at least...