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Toric IOL prediction utilising measured vs theoretical prediction of posterior corneal astigmatism

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Session Details

Session Title: Toric IOL Calculations & Alignment

Session Date/Time: Sunday 23/09/2018 | 08:00-10:00

Paper Time: 08:06

Venue: Room A5

First Author: : G.Barrett AUSTRALIA

Co Author(s): :                        

Abstract Details


The purpose of this study was to compare the error in predicted residual astigmatism utilising direct measurements of posterior corneal astigmatism (PCA) derived from Scheimpflug tomography to the theoretical prediction of PCA incorporated in the Barrett Toric Calculator.


Private practice (Lions Eye Institute) and Tertiary Hospital (SirCharles Gairdner Hospital) Perth, Western Australia.


A retrospective analysis was performed in 100 eyes who had cataract surgery performed with a non Toric IOL((n 46) or Toric IOL (n 54) implanted. The study group was different to the dataset from which an algorithm developed to optimise measured PCA was derived. The centroid error and percentage of patients with an error in predicted residual astigmatism within 0.5 D was calculated using the Barrett Toric Calculator with the default theoretical prediction of PCA or the measured PCA from a Scheimpflug (Pentacam) tomography device and compared to the Holladay calculator utilising Net Corneal Astigmatism provided by the Pentcam .


39% of eyes had an error of prediction within 0.5 D using the Holladay Toric Calculator utilising the True Net Corneal power provided by the Pentacam. 70% of eyes had an error in prediction within 0.5 D of predicted residual astigmatism utilising direct measurements of PCA versus 79% with the theoretical predicted PCA utilising the Barrett Toric Calculator. The differences between the Barrett Toric Calculator using the measured PCA or predicted PCA, were statistically different than the Holladay Toric calculator utilising the True Net Corneal Power, using Wilcoxon non parametric statistical comparison of the absolute median errors.


Both the Measured PCA mode and Theoretical Predicted PCA mode incorporated within the Barrett Toric Calculator proved to be more accurate in predicting residual astigmatism than a standard toric calculator utilising EKR at 4.00 mm or Net Corneal Astigmatism. Direct measurements of the posterior cornea are a useful method to account for PCA but require specific implementation. The theoretical prediction of PCA was more accurate than the measured PCA in this study but the differences were not statistically significant.

Financial Disclosure:

... receives consulting fees, retainer, or contract payments from a company producing, developing or supplying the product or procedure presented

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