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How does preoperative ocular residual astigmatism influence postoperative visual outcome after myopic LASIK?

Poster Details

First Author: M.Casagrande GERMANY

Co Author(s):    T. Katz   A. Frings   J. Steinberg   V. Druchkiv   S. Linke  

Abstract Details



Purpose:

To analyse the effect of preoperative ocular residual astigmatism (ORA) on postoperative outcome in myopic laser in situ keratomileusis (LASIK).

Setting:

University Medical Center Hamburg-Eppendorf , Hamburg, Germany and Care Vision refractive clinics in Germany.

Methods:

Retrospective, cross-sectional data analysis. Randomly selected eyes of myopic candidates scheduled for LASIK were enrolled in this study. Pre- and postoperative refraction, pre- and postoperative ORA and the influence of several parameters on postoperative ORA were analyzed. ORA is defined as the vectorial difference (Alpins vector analysis) between corneal astigmatism and the refractive cylinder at the corneal plane. Treatments were planned according to preoperative refractive data. Pre- and postoperative ORA was compared by dividing ORA SIA (surgically induced astigmatism) and preoperative ORA. Two subgroups were formed: high ORA: ≥ 1.0 and low ORA: < 1.0. Follow up interval was three months and the microkeratome used was the SBK by Moria.

Results:

This study included 1578 eyes of 1578 patients. 516 (32,7%) eyes had a postoperative ORA of 1.00 D or higher. The mean vectoral difference between preoperative and postoperative ORA (ORA SIA) was 0.49 ± 0.51 SD (low ORA) and 0.66 ± 0.67 SD (high ORA). Preoperatively the mean refractive astigmatism was 0.86 ± 0.80 SD with higher value in the group with high ORA (p<0.001). Postoperative UDVA was marginally better in the group with preoperative low ORA (logMAR 0.01 ± 0.11 SD) compared to high ORA (logMAR 0.02 ± 0.13 SD; p<0.001). Postoperative refractive cylinder was lower in the group with preoperative low ORA (0.48 ± 0.30 SD) compared to high ORA (0.52 ± 0.35 SD; p<0.001). The efficacy index (EI; mean 0.93 ± 0.19 SD) as well as the safety index (SI; mean 1.03 ± 0.14 SD) were satisfying in both groups, but with the EI being higher in the group with preoperative low ORA (0.94 ± 0.19 SD) compared to high ORA (0.93 ± 0.19 SD; p<0.001). Ordinary least square estimations show that a high preoperative sphere is a negative predictor of the degree of postoperative ORA.

Conclusions:

High preoperative ORA results in a statistically significant reduced uncorrected visual acuity after myopic LASIK. However comparable efficacy and safety indices support the finding that this trend is clinically not relevant. Future prospective studies are warranted to clarify these trends. FINANCIAL INTEREST: NONE

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