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Quantifying sources of error in toric intraocular lens calculation
Session Title: Assessment of Astigmatism
Session Date/Time: Saturday 05/10/2013 | 11:00-12:30
Paper Time: 11:41
Venue: Main Lecture Hall (Ground Floor)
First Author: : N.Hirnschall AUSTRIA
Co Author(s): : P. Hoffmann S. Maedel P. Draschl M. Weber O. Findl
To evaluate sources of error for residual astigmatism after cataract surgery and toric intraocular lens (t-IOL) implantation using partial least squares regression (PLSR).
VIROS - Vienna Institute for Research in Ocular Surgery, a Karl Landsteiner Institute, Hanusch Hospital, Vienna, Austria
This multicenter study included patients who were scheduled for cataract surgery with implantation of a toric IOL. Optical biometry was performed as standard in each of all three centers in London (UK), Castrop-Rauxel (Germany) and Vienna (Austria). Three months after surgery subjective refraction was performed and the axis of the toric IOL was documented. For analysing purposes, the effect of t-IOL misalignment and the effect of post-operative ACD on the residual astigmatism were calculated. Different factors, such as surgically induced corneal astigmatism (SICA) and inaccuracy of keratometry were weighted regarding to their effect on residual astigmatism using PLSR.
Twohundred-thirty eyes were included in this study. Mean pre- and post-operative corneal astigmatism was -2.2 D (SD: 0.8) and -0.6 D (SD: 0.5), respectively. Mean absolute misalignment of the t-IOLs was 4.5° (SD: 5.1) and the resulting loss of astigmatism reduction was 12.5% (SD: 11.5). Highest influencial factor on the refractive astigmatism surprise was the inaccuracy of the pre-operative corneal keratometry.
Although residual astigmatism is related to toric IOL misalignment in some cases, in the majority of cases the inprecise keratometry of the cornea is the main source of error, especially in eyes with relatively low pre-operative corneal astigmatism.