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Session Title: Special Cases
Session Date/Time: Monday 07/10/2013 | 17:00-18:30
Paper Time: 17:42
Venue: Elicium 1 (First Floor)
First Author: : A.Frings GERMANY
Co Author(s): : T. Katz J. Steinberg V. Druchkiv G. Richard S. Linke
To analyze the influence of specific factors on the preexisting ocular residual astigmatism (ORA) in patients scheduled for LASIK for myopic astigmatism.
University Medical Center Hamburg-Eppendorf, Germany, and Care Vision Refractive Centers, Germany.
We studied the records of 3011 eyes from 3011 consecutive myopic patients (1169 male, 1842 female; mean age 35.0 ± 10.0 years) who were scheduled for LASIK to investigate the influence of age, sex, ocular dominance, subjective cylinder and SimK, subjective sphere, and mesopic pupil size on preexisting ORA. The ORA was determined using vector analysis. Two subgroups defined by the ratio of ORA to preoperative refractive cylinder (R) were formed (ORA/R of ?1.00 D vs. <1.00 D).
We obtained a mean preoperative subjective sphere of -3.39 ±1.90 D (range, -8.00 to 0.00 D), and a mean subjective cylinder of -0.99 ±0.78 D. The mean ORA was 0.75 ±0.39 D (range, 0.00 to 2.00 D), 1380 (46%) eyes had ORA of ?1.00 D. Eyes with low ORA had significantly higher magnitudes of subjective cylinder and SimK (P<0.001) (= cylinder at the corneal plane). A difference of 0.20 D in subjective sphere was obtained between low and high ORA groups thereby indicating that eyes with high ORA were statistically significant (P=0.015) more myopic. By applying Ordinary-least-square-estimation we showed that mesopic pupil size, male sex, and ocular dominance were negative predictors for preoperative ORA, while age (=older patients) and eyes with higher preoperative subjective sphere had higher preoperative ORA (= age and subjective sphere were positive predictors for (high) ORA). This was confirmed by Odds Ratios obtained from logistic model analysis.
We evaluated the effect of specific factors on preexisting ORA in eyes planned for refractive surgery and found a statistically significant difference in subjective cylinder between eyes with low or high ORA. Eyes with low ORA were associated with a significantly higher refractive cylinder. Accordingly the preoperative refractive astigmatism was located mainly at the anterior corneal surface. A larger mesopic pupil size, male sex, and ocular dominance were negative predictors for high ORA. This means these factors are indicating low ORA thereby telling the surgeon that the origin of the total net astigmatism is mainly located at the corneal plane. The assessment of the preoperative eye should therefore take into account the interaction between ORA and those factors as LASIK is more successful in eyes where the cylinder is mainly originated from the cornea. However, whether different preexisting magnitudes of ORA are influencing the post-LASIK outcome in terms of efficacy, safety and predictability should preferably be analyzed in a future study.
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