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Correcting corneal astigmatism with toric multifocal IOLs: back surface toricity vs front surface asymmetry – what is the key?

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Session Details

Session Title: Refractive Lens Exchange

Session Date/Time: Tuesday 16/09/2014 | 16:30-18:00

Paper Time: 16:48

Venue: Capital Hall A

First Author: : B.Gjerdrum NORWAY

Co Author(s): :    T. Olsen   E. Støle           

Abstract Details


The purpose of this work was to study the possible improvement in clinical predictability of taking the posterior corneal toricity into account.


Private refractive surgery clinic Memira, Stavanger, Norway.


The study involved a consecutive series of 130 eyes from 74 patients undergoing RLE surgery in the period from september 2010 to July 2011 with the implantation of an Alcon ReSTOR 3 multifocal toric IOL in at least 1 eye. Preoperative measurements were done with Orbscan IIz and Zeiss IOLMaster. Corneal astigmatism was evaluated using ”LDK (Least Difference K-values)” of the cornea curvatures. The ”Total Average Astigmatism” was calculated from the ”Axial Total” k-values of the Orbscan measurements representing the total refraction of both the front and the back surface of the cornea. Toric lens calculations were performed with the online Alcon Toric Calculator. The outcome measure was the difference between the effect of IOL cylinder power at the cornea plane and the actual postoperative refractive cylinder.


The predictions based on the ”Axial Total LDK” was found to show the highest correlation with the actual refractive cylinder and the lowest predictability was found using the 'Axial Total Average”. The two methods were found to predict the refractive cylinder within +/- 0,75 D in 96% and 84% of the cases, respectively (p < 0.01). The predictions based on the anterior astigmatism only - 'Anterior LDK' - was within +/- 0,75 D in 91% of the cases, which was slightly worse than ”Axial Total LDK” (p < 0.05).


The prediction of the effective refractive cylinder following toric implantation can be improved by taking the back surface of the cornea into account. However, the improvement is only slight as compared to predictions based on the anterior surface only. The reason for this small difference appears to be measurement errors associated with the recording of the posterior toricity and othe errors such as axis misalignment.

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