Toric Intraocular Lens Results Considering Posterior Corneal Astigmatism with Online Calculators: Phacoemulsification vs. Femtosecond

Joaquín Fernández,Noemí Burguera,Nuria Garzón,Patrizia Salvestrini,Manuel Rodríguez-Vallejo

doi:10.3390/opt2030017

Joaquín Fernández, Noemí Burguera + Show 3 more

Open Access

https://doi.org/10.3390/opt2030017

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Journal: Optics	Publication Date: Sep 3, 2021
Citations: 2	License type: CC BY 4.0

Affiliation: Universidad Complutense de Madrid

Abstract

To evaluate the prediction error (PE) obtained in Phacoemulsification (Phaco) or Femtosecond (Femto) surgeries without considering posterior corneal astigmatism correction (non-PCA) versus the correction based on Abulafia-Koch + Medicontur (AK) and Barrett calculators in toric intraocular lens (IOL) power calculation. 58 right eyes were retrospectively retrieved from our database. Two groups formed by 28 and 30 eyes depending on the surgery type, Phaco or Femto respectively, were defined. Astigmatism PE were evaluated considering the approach used for calculation of the implanted IOL power (AK) versus the estimation of PEs in non-PCA and Barrett formula. A doubly-multivariate analysis was conducted to assess the differences between-surgery types, within-methods of calculation, and interaction. Mean centroid PE was significantly different between non-PCA, AK and Barrett approaches (p < 0.0005), and neither differences (p < 0.239) nor interaction (p = 0.672) between Phaco or Femto were found. Post-hoc univariate analysis showed a higher PE for the x-component of the non-PCA method versus AK (0.15 D, p < 0.0005) and non-PCA versus Barrett (0.18 D, p < 0.0005), though no differences were found between AK and Barrett (0.03 D, p = 0.93). Against-the-rule under-correction and with-the-rule overcorrection were found in both arms when PCA was not considered. Both calculators provide comparable clinical results.

Highlights

Traditionally only anterior corneal astigmatism has been considered to calculate the intraocular lens (IOL) power, posterior corneal surface contributes to total corneal astigmatism
The refractive power of the posterior surface is much smaller than the anterior surface due to the small difference in refractive index between the cornea and the aqueous humor, an overcorrection in with-the-rule (WTR) and an under-correction with against-the-rule (ATR) anterior corneal astigmatism could be expected if the posterior corneal astigmatism (PCA) is not considered in the calculation [1]
Some authors estimate PCA on the basis of anterior corneal astigmatism [1,2,3,4], others measure the posterior astigmatism with tomography [5] or estimate total corneal astigmatism based on the anterior-to-posterior corneal cylinder power ratio [6]

Summary

Introduction

Traditionally only anterior corneal astigmatism has been considered to calculate the intraocular lens (IOL) power, posterior corneal surface contributes to total corneal astigmatism. The refractive power of the posterior surface is much smaller than the anterior surface due to the small difference in refractive index between the cornea and the aqueous humor, an overcorrection in with-the-rule (WTR) and an under-correction with against-the-rule (ATR) anterior corneal astigmatism could be expected if the PCA is not considered in the calculation [1]. There are different methods to assess total corneal astigmatism in order to calculate the IOL power. The Abulafia-Koch (AK) regression formula for IOL power calculates the estimated total corneal astigmatism using standard keratometry (K) measurements [4]. This formula adjusts standard K measurements to the estimated net corneal power, thereby

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