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J. G. Grigsby, T. R. Walters, M. D. Tschoepe, B. J. Cook, D. K. Neely, R. G. Sheets, M. Miller, K. Vasquez; Predictability of the Final Refractive Outcome of LASEK From Early Pre-Operative Refractions. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4207.
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: Laser epithelial keratomileusis (LASEK) is an alternative to PRK developed to reduce the chance of complications that can occur when a flap is created during LASIK. The healing process in LASEK is unique when compared to LASIK in the fact that vision recovery is correlated with the formation of new epithelium. It is unique compared to the healing process in PRK in the fact that while both require a new epithelial layer to form, with LASEK there are interactions occurring with the co-existing pre-procedure epithelium. Our hypothesis was that these interactions result in some early post-procedure refractive anomalies that do not correlate with the final refractive result.
A retrospective analysis of LASEK was performed on 110 eyes of 57 patients of which all were available for follow-up at a 2 week, 1 month, 3 month, 6 month and 1 year intervals. Procedures were performed on prescriptions whose pre-procedure myopic spherical equivalent refractions ranged from -0.50 to -7.63 diopters (D) (mean -4.40 D). LASEK was performed with a 20" exposure of a 20% solution of dehydrated ETOH in sterile water. Ablations were created with a Visx Star 4 or Star 4 IR platform using standard, Customvue©, or Customvue IR©. Ablations deeper than 100 microns were treated post-operatively with a 15" exposure of 0.02% MMC. Biomicroscopy and refractions were performed at 2 week, 1 month, 3 month, 6 month and 1 year.
Mean refractive spherical equivalent refractions done at 2 weeks, one month, three months, six months and 1 year were all very similar; +0.06 D, +0.05 D, +0.07 D, 0.00 D and +0.06 D respectively. However, while the means were similar between groups, variances between groups differed significantly. Variances were not significantly different between the two week and one month group, but the variances of these groups were significantly different than both the three month and one year groups. The variances of the three month and the one year data were similar. The amount of astigmatism between 2 weeks and 1 year were statistically different, 0.55 D and 0.27 D respectively (p<0.001).
While the statistical means of spherical equivalent refractions done on LASEK patients during this time period may be similar, there is greater variability in those refractions done at 2 weeks and 1 month compared to those done at 3 months or one year. Over time as LASEK heals there is a trend toward less refractive variability from the target prescription and less astigmatism.
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