Changes of posterior corneal XXXX and tilt after myopic laser in situ keratomileusis.

@entity940 @entity2687 @entity1714
PURPOSE: The purpose of this study was to assess the changes of posterior corneal @entity940 and tilt after laser in situ keratomileusis (LASIK) and to correlate these changes with the amount of correction and the residual stromal bed thickness. METHODS: This prospective nonrandomized (self-controlled) comparative trial included 57 eyes from 14 females and 15 males, whose mean age (+/- standard deviation [SD]) at the time of surgery was 33 +/- 9 years (range, 19-53), with a spherical equivalent (SEQ) of -1.00 to -15.50 (mean, -5.07 +/- 2.81) diopters (D). All LASIK procedures were accomplished with the Keratom II Coherent-Schwind excimer laser and the Moria Model One microkeratome (150-microm head). Subjective refractometry, Orbscan slit-scanning corneal topography analysis, and pachymetry were performed before and 3 months after LASIK for @entity1714 (n= 35; -1.00 to -15.50 D [mean, -4.75 +/- 3.07]) or myopic @entity940 (n= 22; sphere, 0.00 to -9.75 D [mean, -4.75 +/- 2.36]; cylinder, -0.75 to -3.50 D [-1.68 +/- 0.86]). Intended ablation depth ranged from 12 to 108 (mean, 48 +/- 22) microm. Topographic raw data were decomposed into a set of Zernike polynomials as published in detail previously, and parameters for detection of asymmetric mechanical deformation of the cornea were derived. Posterior corneal @entity940 and tilt before and after LASIK were compared, and changes in these variables were correlated with the SEQ change (DeltaSEQ) and the @entity2687 ( @entity2687 ). RESULTS: The @entity2687 after LASIK ranged from 186 to 373 (mean, 280 +/- 42) microm. Overall, @entity940 (0.19 +/- 0.07 D/0.22 +/- 0.13 D; p= 0.80) and tilt (3.58 +/- 0.35 degrees /3.65 +/- 0.48 degrees; p= 0.61) did not change significantly by 3 months after LASIK. In eyes with @entity2687 < or =250 microm, the average change in @entity940 (0.05 +/- 0.11 versus 0.01 +/- 0.13 D; p= 0.46) and tilt (0.21 +/- 0.45 degrees versus 0.04 +/- 0.55 degrees; p= 0.30) was not greater than in eyes with @entity2687 > 250 microm. Change in @entity940 (p= 0.19) and tilt (p= 0.56) did not correlate with the @entity2687 during LASIK. CONCLUSIONS: Zernike decomposition of topographic height data discloses that no significant asymmetric mechanical deformation of the posterior corneal curvature occurs after myopic LASIK. Further studies with long-term follow-up are needed to clarify whether this symmetry of the posterior corneal surface can indeed be preserved over time after LASIK if the @entity2687 is < 250 microm.
