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IOL formula accuracy in Fuchs endothelial corneal dystrophy

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Session Details

Session Title: Cataract Surgery Outcomes: IOL Power Calculations

Session Date/Time: Sunday 08/10/2017 | 14:30-16:00

Paper Time: 14:42

Venue: Meeting Center Room I

First Author: : P.Gil PORTUGAL

Co Author(s): :    P. Ramos   A. Rosa   M. Quadrado   J. Povoa   C. Lobo   J. Murta     

Abstract Details


Patients with corneal endothelial dysfunction often present a myopic shift as a result of subclinical stromal swelling. In patients with Fuchs endothelial corneal dystrophy (FECD) undergoing cataract surgery without the need for endothelial transplant, optical biometry may lead to unacceptable prediction errors, as standard mean anterior keratometry does not account for the disease-related flattening of posterior corneal curvature. The purpose of this work is to compare the accuracy of a 3rd generation formula (SRK/T), a newer generation formula (Barrett Universal II) and a pattern-recognition method (Hill-RBF) in FECD patients and in controls.


Ophthalmology Department, Centro Hospitalar e Universitário de Coimbra, Coimbra, Portugal.


Retrospective case-series. Consecutive FECD patients submitted to cataract surgery between 1st January 2013 and 31st December 2016 were reviewed. Prior or combined corneal transplant cases were excluded. Biometric measurements for IOL calculation were derived from Allegro BioGraph and topographic maps were acquired with Orbscan IIz. A control group matched for axial length, anterior chamber depth and mean anterior keratometry was included. SRK/T was calculated with User Group for Laser Interference Biometry optimized constants, Barrett Universal II with the implanted IOL’s A-constant and lens factor provided by the original author, and Hill-RBF according to the manufacturer’s online calculator.


A total of 46 eyes were included, 20 of 15 patients and 26 of 26 controls. Mean errors for the FECD and control groups were, respectively, 0.09±0.90 vs. 0.06±0.41 (p=0.634) for SRK/T, -0.27±0.84 vs. 0.11±0.37 (p=0.002) for Barrett II and -0.42±0.87 vs. 0.36±0.41 (p<0.001) for Hill-RBF. Median absolute errors were not significantly higher in patients comparing to controls except for Hill-RBF (SRK/T: 0.33 vs. 0.26, p=0.766; Barrett II: 0.56 vs. 0.27, p=0.137; Hill-RBF: 0.64 vs. 0.30, p=0.037). The correlation between preoperative corneal pachymetry and prediction errors did not reach significance for all formulas.


The present study suggests that our current IOL formulas result in a more negative prediction error in FECD patients than in controls. This myopic shift might reflect the incorrect estimation of corneal power solely derived from mean anterior keratometry, not accounting for disease-induced corneal thickening and consequent posterior corneal curvature flattening. A pattern recognition-based formula like Hill-RBF leads to unacceptable outcomes, possibly because this purely data-driven approach has insufficient data representative of optical systems with aberrant anatomical relations between anterior and posterior corneal curvatures.

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