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J. W. McLaren, S. V. Patel, C. B. Nau, E. J. Winter, W. M. Bourne; Corneal Wavefront Errors One Year After LASIK: A Paired Comparison Between Flap Cut With a Femtosecond Laser and With a Mechanical Microkeratome. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2360.
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© ARVO (1962-2015); The Authors (2016-present)
In a paired-eye study, we compared wavefront errors that originated with corneal topography after LASIK with the flap cut by a femtosecond laser (bladeless) to wavefront errors after LASIK with the flap cut by a mechanical microkeratome.
Twenty patients received non-wavefront-guided LASIK for myopia or myopic astigmatism. One eye of each patient was randomized to flap creation with a femtosecond laser with intended flap thickness of 120 µm, and the other eye to flap creation with a microkeratome blade with intended flap thickness of 180 µm. Preoperative spheroequivalent refractive error was -3.7 ± 1.6 D (mean ± SD) and -3.7 ± 1.7 D for eyes to be treated by bladeless and microkeratome respectively. Corneal topography was recorded by using a Humphrey Atlas Corneal Topography System before surgery and at 1, 3, 6 and 12 months after surgery. Wavefront errors over a 6-mm pupil were calculated by VOLCT (Sarver and Associates, Inc., Celebration, FL) and expressed as Zernike polynomials to 6th order. The root sum of squares of sphere, coma, and other high-order terms were compared after surgery to before surgery, and between treatments at each visit by using paired t-tests with Bonferroni-adjustment for multiple comparisons.
Spherical aberration (Z40) increased from 0.27 ± 0.09 µm before to 0.42 ± 0.16 µm 1 month after bladeless LASIK (p<0.001) and increased from 0.26 ± 0.09 µm before to 0.39 ± 0.15 µm 1 month after LASIK with the microkeratome (p<0.001). Coma (Z3-1 and Z31) increased from 0.27 ± 0.20 µm before to 0.46 ± 0.27 µm 1 month after bladeless LASIK (p = 0.04) but did not increase significantly after LASIK with the microkeratome (0.28 ± 0.24 µm before to 0.37 ± 0.26 µm at 1 month, p = 0.21). Spherical aberration remained elevated after both treatments to 1 year (p<0.001) while coma was elevated after bladeless treatment to 6 months (p<0.04) but was not significantly elevated at 1 year (p=0.053). Aberrations were not different between treatments at any time (p>0.09). Minimum detectable difference between treatments was 0.10 µm for sphere and 0.16 µm for coma (α=0.05, ß=0.20, 5 comparisons).
Spherical aberration from the corneal surface increases and remains elevated for at least a year after LASIK with the flap cut by either a femtosecond laser or by a microkeratome. Coma increases after treatment with the femtosecond laser for 6 months, although it does not increase significantly after treatment with a microkeratome. These aberrations are not different between treatments.
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