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

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.

Saving of Time Using a Software-Based versus a Manual Workflow for Toric Intraocular Lens Calculation and Implantation

“…Whereas early formulas solely considered the keratometry values (K) of the anterior corneal surface, state-of-the-art formulas consider the total keratometry (TK) including the values of the anterior and posterior corneal surface. This is due to several studies stating that the posterior corneal surface significantly contributes to the total corneal astigmatism [ 6 ], and its consideration thus leads to a superior postoperative prediction accuracy [ 7 ].…”

Comparison of the Barrett toric calculator using measured and predicted posterior corneal astigmatism and the Kane and Abulafia-Koch calculators

“…In accordance with several studies indicating that posterior corneal astigmatism (PCA) contributes to overall corneal astigmatism, most current toric IOL calculators incorporate PCA in their algorithm. [5][6][7][8][9][10][11][12] Two strategies enable this: direct measurement of the PCA by new technologies, such as Scheimpflug and optical coherence tomography devices, or using adjustment methods that account for the PCA power and axis. The Barrett toric calculator (available at: https://ascrs.org/ tools/barrett-toric-calculator, accessed on July 12, 2022) implements both options.…”