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C. T. Hood, R. R. Krueger, S. E. Wilson; The Effect of Femtosecond Laser Flap Thickness and Flap Diameter on Wavefront Aberrations After Customized LASIK. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2870.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the effect of femtosecond laser flap thickness on higher order aberrations (HOA) after customized myopic LASIK.
We retrospectively reviewed the charts of patients who underwent wavefront-guided customized myopic LASIK by one surgeon at our institution with the Alcon LADARVision4000 excimer laser (Alcon Laboratories Inc., Ft. Worth, TX), with flap creation using the IntraLase femtosecond laser (IntraLase Corp., Irvine, CA), between 2006 and 2009. Eyes were excluded if they were not targeted for emmetropia, had previous refractive surgery, or flap related complications. Grouped RMS values for total aberrations, total HOA, coma, spherical aberration, and other HOA were obtained using the LADARWave system (Alcon Laboratories, Ft. Worth, TX) using a 6.0 mm pupil diameter. Only patients with three month post-operative wavefront scans were included. If a patient had bilateral surgery, one eye was excluded at random. Patients were stratified according to intended flap thickness and the change in HOA from pre-operative to three months post-operative was compared between the groups. The relationship between "actual" flap thickness, as calculated by intraoperative ultrasonic pachymetry, and change in HOA was evaluated univariably and multivariably. To account for multiple analyses, a Bonferroni correction was made to a P value of 0.05 to determine significance.
171 eyes were included in the analysis, with age 40.3±10.2 yrs and manifest refraction spherical equivalent (MRSE) 4.04±1.88 diopters. At three months, the mean Snellen visual acuity was 20/22, with 97% of eyes having acuity of ≥20/40, 49% of eyes having acuity of ≥20/20. On average, total HOA, coma, spherical aberration, and other HOA were all increased. Comparing eyes with intended flap thickness of 90 or 100 microns to those of 110 microns, there was no difference in the change in total HOA, coma, spherical aberration, or other HOA. In a multivariate model, MRSE was highly associated with the induction of total HOA, coma, and spherical aberration. There was no correlation between "actual" flap thickness and higher order aberrations in a univariate or multivariate analysis that adjusted for MRSE, age, and gender.
In eyes undergoing customized myopic LASIK, with flap creation using the femtosecond laser, intended and "actual" flap thickness did not have a significant effect on the induction of higher order aberrations. The level of myopic correction (MRSE) was highly associated with the induction of total HOA, coma, and spherical aberration.
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