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Sources of error in toric intraocular lens power calculation

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Session Details

Session Title: Pseudophakic IOLs: Toric & Multifocal

Session Date/Time: Tuesday 08/09/2015 | 08:00-10:30

Paper Time: 08:00

Venue: Room 11

First Author: : N.Hirnschall AUSTRIA

Co Author(s): :    S. Norrby   E. Winter   C. Leisser   P. Hoffmann   O. Findl        

Abstract Details


To evaluate the influencing factors on remaining astigmatism after implanting a toric intraocular lens (IOL) during cataract surgery using Gaussian error propagation.


Hanusch Hospital, Vienna Austria and Private Clinic in Castrop-Rauxel, Germany


In this study, cataract patients of three different centers (Hanusch Hospital, Vienna, Austria; Castrop-Rauxel, Germany; and Moorfields Eye Hospital, London, UK) that received toric IOLs were included as well as data from the literature. All parameters influencing the post-operative remaining astigmatism were detected by screening the recent literature. In a next step mean and standard deviation as well as reproducibility of pre-operative measurements were taken from our data set, or from the recent literature. Then thick lens ray tracing and Gaussian error propagation analysis was used to evaluate the influence of different parameters on the remaining post-operative astigmatism.


In total, 235 eyes of 200 patients were included from the three centers and 42 papers from the literature were screened. Mean corneal astigmatism measured pre-operatively with the optical biometry device was -2.24 D (SD: 0.87; -5.75 D to -1.00D). Mean absolute and vector difference between the aimed and the post-operatively measured astigmatism were 0.48D (SD: 0.37; 0.00 to 2.05D) and 0.73D (SD: 0.46, 0.031 to -2.20), respectively (p=0.576). Results of the Gaussian error propagation analysis will be shown at the meeting.


Main source of error when using toric IOLs is the pre-operative measurement of corneal astigmatism, especially in eyes with low astigmatism. The influence of the post-operative anterior chamber depth on the cylindrical power of toric IOLs and the effect of misalignment on the reduction of the astigmatism reducing effect can be easily calculated.

Financial Interest:


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