Toric Intraocular Lens Calculation Considering Anterior Surgically Induced Astigmatism and Posterior Corneal Astigmatism

ABSTRACT

Purpose

To evaluate the prediction error (PE) after applying the Abulafia–Koch formula in an online calculator with and without consideration of anterior corneal surgically induced astigmatism (SIA_Cornea).

Methods

SIA_Cornea models were calculated with a historical database of 204 right eyes (REs) from a single surgeon, either for manual (2.2 mm) or femtosecond (2.5 mm) temporal clear corneal incisions. PE was assessed in 58 REs operated by the same surgeon with a monofocal toric IOL and calculated, considering the PCA estimation in an online calculator with the combination of each one of the following SIA_Cornea calculation approaches: (A) considering only significant centroids after stratification, (B) all centroids after stratification and (C) a single centroid without stratification.

Results

The consideration of all centroids resulted in an underestimation of SIA_Cornea in cases of preoperative against-the-rule astigmatism (ATR-A) and an overestimation in with-the-rule astigmatism (WTR-A). After stratification, SIA_Cornea was only significant in preoperative ATR and oblique astigmatism cases for femtosecond incisions. PE considering PCA only was 0.03@160º. The combination with SIA_Cornea resulted in a WTR-A surprise in preoperative ATR-A and WTR-A, however only being significant for preoperative ATR-A in calculation approaches B (0.29@84º) and C (0.21@80º). SIA_Cornea addition to PCA estimation only reduced the centroid for oblique preoperative astigmatism.

Conclusions

Surgeons should consider the calculation of the SIA_Cornea after stratification by astigmatism type when using the same incision location (i.e. temporal). However, SIA_Cornea derived from the anterior corneal surface should not be combined with PCA estimation for IOL power calculations.

KEYWORDS:

• Surgically induced astigmatism
• posterior corneal astigmatism
• cataract
• toric intraocular lens
• prediction error

Acknowledgments

The authors would like to thank the reviewers for their exceptional contributions to improve the first draft of this manuscript.

Disclosure statement

Dr. Fernández is consultant from Medicontur and Rodríguez-Vallejo M is the developer of the system used to calculate the surgically induced astigmatism and to measure visual acuity. The remaining authors have nothing to disclose.