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K. A. Kerns, B. H. Jeng, R. R. Kruger, A. S. Roth, W. J. Dupps, Jr.; Early Refractive Outcomes of Wave-Front Guided Sub-Bowman's Keratomileusis (SBK) With 110µm and 90µm Femtosecond Flaps. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5640.
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To compare the refractive outcomes of thin-flap LASIK with 90µm and 110µm femtosecond flaps to determine if surgeons need to account for their choice of flap thickness in the treatment offset.
We performed a retrospective, IRB-approved chart review of 178 consecutive patients who had CustomCornea LASIK for myopia (Alcon LADARVision 6000) with femtosecond flaps (Intralase fs 60) performed by two surgeons (RK and WD). Eyes with 3-5 month follow-up were divided into 2 groups: 88 eyes with 90µm flaps and 90 eyes with 110µm flaps. Preoperative and surgical variables in each group were compared using student t-test with a p value < .05 indicating significance.
Preoperative central corneal thickness (CCT) differed between in the 90µm (543±22µm) and 110µm groups (557±33µm, p=0.002), while attempted correction, simulated keratometry and patient age did not (p>0.09). Surgeon offsets differed between the 90µm (+0.34±0.28D) and 110µm groups (+0.12±0.30D, p<0.001). Regression analysis demonstrated no correlation between postoperative spherical equivalent (SE) refractive error and CCT. Visual acuity outcomes were no different in the 2 groups. Actual postoperative SE was no different between the 90µm (-0.09±0.39D) and 110µm (-0.10±0.36D) groups (p=0.9) but differed slightly after adjustment for the offset (p=0.1). Intended and measured flap thickness (by intraoperative subtractive pachymetry) were poor predictors of adjusted SE refractive error in single predictor and multivariate analyses, and surgeon offset only explained a small portion of the variance in refractive outcome (R2=4.8%, p=0.003).
The choice of a 90µm vs.110µm femtosecond flap had no measurable effect on early refractive outomces in custom myopia treatments.Though surgeons tended to treat thinner corneas with 90µm flaps and apply slightly larger positive SE offsets in this group, intended flap thickness nevere demonstrated significance as a predictor of refractive outcome. Offset adjustments on the basis of intended flap thickness in the 90-110µm range do not appear to be necessary.
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