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Comparison of different IOL calculations for the implantation of toric IOLs in patiens with keratoconus

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First Author: V.Webers THE NETHERLANDS

Co Author(s):    M. Vandevenne   N. Visser   N. Bauer   T. Berendschot   R. Nuijts        

Abstract Details

Purpose:

To evaluate the accuracy of different IOL calculations for the implantation of toric IOLs in patients with keratoconus

Setting:

University Eye Clinic Maastricht, the Netherlands

Methods:

A total of thirty-six eyes of 25 patients with stable mild to moderate keratoconus (Krumeich stage 1 and 2) underwent cataract surgery with toric IOL implantation (Acrysof SN6AT3-T9 or Rayner T-flex). Back-calculations were performed for four different IOL calculations: first generation toric calculator (1st), K-values of biometry (IOLmaster, IOlm-Barrett), Scheimpflug (Pentacam, SimK-Barrett), and measured posterior cornea astigmatism (PCA) (Pentacam, PCA-Barrett) in the Barrett Toric Calculator. For residual astigmatism, vector analyses was performed for the mean prediction error (ME), mean absolute prediction error (MAE) and correction index (CI).

Results:

The mean preoperative corneal astigmatism was 3.88±1.30D (range 1.42-6.38D). ME was respectively 0.55±0.59D*, 0.67±0.65D*, 0.06±0.72D, -0.19±0.87D for 1st, IOLm-Barrett, SimK-Barrett, and PCA-Barrett (*significant different from zero). MAE was respectively 0.63±0.50D, 0.77±0.53D, 0.55±0.45D, and 0.67±0.57D for 1st, IOLm-Barrett, SimK-Barrett, and PCA-Barrett (p>.05). CI was significantly closer to ideal 1.0 for the SimK-Barrett (1.07±0.24) and PCA-Barrett (1.06±0.45) methods compared to 1st (1.20±0.21) and IOLm-Barrett (1.25±0.24) methods (p<.05). Percentage of patients with correction of astigmatism within 0.5D was respectively 46%, 34%, 59%, 45% for 1st, IOLm-Barrett, SimK-Barrett, and PCA-Barrett method.

Conclusions:

Performing toric IOL calculations in keratoconus eyes is complex. The use of a 1st generation toric calculator or the K-values measured with biometry in the Barrett Toric Calculator results in a general overcorrection of pre-existent corneal astigmatism. Using K-values measured with Scheimpflug imaging (with or without measured posterior astigmatism) showed lower mean prediction errors and less overcorrection.

Financial Disclosure:

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