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C.B. Nau, J.C. Erie, D.O. Hodge, J.W. McLaren, W.M. Bourne; Central Epithelial and Stromal Thickness 5 Years After LASIK and PRK . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4387.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To examine changes in epithelial and stromal thickness for 5 years after LASIK (laser in situ keratomileusis) and PRK (photorefractive keratectomy). Methods: Seventeen eyes of 11 patients were treated with LASIK to correct refractive errors between –2D and –11D. Stromas were cut with a Hansatome microkeratome with a planned 180 µm–depth. Eighteen eyes of 12 patients were treated with PRK to correct refractive errors between –1.5D and –5.75D. Central corneas were examined by confocal microscopy (Tandem Scanning, Reston, VA) before and at 1 month, 3 months, 6 months, 1 year, 2 years, 3 years, and 5 years after the procedure. Epithelial thickness was determined from the number of video frames between the brightest image of epithelial cells and either the subbasal nerve plexus or the intensity peak just anterior to the first keratocytes if nerves were not visible. If neither endpoint was present after LASIK, thickness was not determined. If neither was present after PRK, the first frame of anterior keratocytes was used as the endpoint. Epithelial thicknesses after treatment were compared to thickness before treatment, and stromal thicknesses were compared to stromal thickness at 1 month. Significances of differences were determined by using Generalized Estimating Equation models (to account for potential correlation between eyes from the same patient) and the Bonferroni method to correct for multiple comparisons. Results: Mean epithelial thickness before LASIK was 41 ± 4 µm (± SD, n=17). It increased to 50 ± 5 µm at 1 month (p<0.001, n=12) and 53 ± 5 µm (p<0.001, n=16) at 5 years. Mean stromal thickness was 391 ± 39 µm (n=17) one month after LASIK, and 393 ± 31µm (p=1.0, n=16) at 5 years. Mean epithelial thickness before PRK was 44 ± 5 µm (n=18). At 5 years it was 45 ± 5 µm (p=1.0, n=18), although at 3 years it had increased to 49 ± 7 µm (p<0.001, n=18). Stromal thickness was 395 ± 41 µm (n=15) 1 month after PRK, and 416 ± 47 µm (p=0.12, n=18) by 5 years. Conclusions: Epithelial thickness increases after LASIK and remains elevated for at least 5 years. The stroma does not thicken or thin during the same time, after the initial surgical reduction. After PRK the epithelial and stromal thicknesses do not change for at least 5 years.
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