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Session Title: Intraoperative Biometry and Correction of Astigmatism
Session Date/Time: Monday 07/10/2013 | 08:00-10:00
Paper Time: 09:39
Venue: Main Lecture Hall (Ground Floor)
First Author: : G.Savini ITALY
Co Author(s): : K. Naeser
To examine the accuracy in the correction of astigmatism following Alcon Acrysof toric intraocular lenses (IOLs).
We prospectively used preoperative simulated keratometry (Keratron, Optikon 2000, Italy) and the Alcon web calculator to predict the postoperative refractive astigmatism following Acrysof toric IOL implantation in 25 eyes of 18 patients. We also registered refractive astigmatism, postoperative simulated keratometry and the IOL axis 3 months after surgery. All refractive and keratometric data were transformed to polar values. The refractive astigmatism was compared to both the preoperatively predicted astigmatism and the astigmatism derived from postoperative keratometry and the observed IOL position.
The refractive astigmatism was significantly overcorrected by 0.47 D (SD: 0.51 D) compared to web calculator data, and by 0.46 D (SD: ± 0.58 D) for postoperative keratometric data. The error varied as a function of the direction of the steeper anterior corneal meridian, amounting to 0.66D overcorrection for with-the-rule and 0.05 undercorrection D for against-the-rule astigmatism. No significant torsion (rotation of cylinder axis) was observed.
The observed overcorrection was not caused by errors in alignment of incision or IOL axis, as the pre- and postoperative data were similar. The error is due to the negative power of the posterior corneal astigmatism, which is not measured with standard keratometry. It is possible to eliminate this overcorrection in groups of eyes using correction factors. However, an accurate calculation of toric IOL power in the individual eye requires exact measurement of both anterior and posterior corneal astigmatism.
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