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J.W. McLaren, J.C. Erie, C.B. Nau, W.M. Bourne; Central Epithelial and Stromal Thickness 3 Years after LASIK and PRK . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2674.
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Purpose: To examine and compare the long-term changes in thickness of the corneal epithelium and stroma after myopic laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). Methods: Seventeen eyes of 11 patients were treated with LASIK, with a planned 180-µm flap (Hansatome) to correct refractive errors between –2.0 D and –11.0D. Twenty-four eyes of 14 patients were treated with PRK (epithelial removal by laser-scrape) to correct refractive errors between –1.5 D and –5.75 D. Central corneas were examined by confocal microscopy (Tandem Scanning, Reston, VA) before and at 1 month, and 1, 2, and 3 years after treatment. Epithelial thickness was determined from the number of video frames between the surface epithelium and the subbasal nerve plexus. All distances in the cornea were calibrated from measurements of contact lenses with known thickness. Stromal thickness was the distance between the most anterior keratocytes and the endothelium. Epithelial and stromal thickness at 1, 2, and 3 years were compared (paired t-tests, Bonferroni-adjusted for multiple comparisons) with the same thickness before treatment and at 1 month respectively. Results: Epithelial thickness was 41 ± 4 µm (mean ± SD) before LASIK and increased to 45 ± 7 µm (ns), 51 ± 7 µm (p<0.001), 50 ± 6 µm (p<0.001) at 1, 2, and 3 years after LASIK respectively. Epithelial thickness was 44 ± 2 µm before PRK, and increased to 56 ± 5 µm (p<0.001), 56 ± 6 (p<0.001), and 57 ± 7 (p<0.001) by 1, 2, and 3 years after PRK. After both procedures, thickness of the stroma did not change significantly after the first month. After LASIK stromal thickness was 391 ± 39 µm and 401 ± 36 µm at 1 month and 3 years respectively, and after PRK stromal thickness was 429 ± 44 µm and 437 ± 54 µm at 1 month and 3 years. Conclusions: The corneal epithelium thickens by 24 – 27% by 1 year after treatment with PRK and by 2 years after LASIK, and does not return to pre-treatment thickness by 3 years. Thickness of the stroma that remains after these procedures is stable during at least the first 3 years.
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