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L. Racine, T. Hoang–Xuan, D. Gatinel; Epithelium Contribution on Corneal Topography in Patients Undergoing Myopic Photorefractive Keratectomy (PRK) . Invest. Ophthalmol. Vis. Sci. 2006;47(13):574.
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© ARVO (1962-2015); The Authors (2016-present)
To assess the variations of corneal topographic characteristics after removal of the epithelium in patients undergoing myopic PRK.
44 eyes of 25 patients underwent corneal topography exam with Orbscan before and after removal of the corneal epithelium during myopic PRK. On each exam, pachymetry, Simulated Keratometry at 3 mm (Sim K’s), central 3.0 mm irregularity index, Best Fit Sphere (BFS) radius, and asphericity were recorded. All patients underwent myopic PRK laser treatment as planned.
The mean difference in pachymetry was 37.84 µ ± 9.82 (range 19 to 58); this calculation gives an estimate of the corneal epithelium thickness. The mean BFS radius was 7.77 ± 0.30 mm (range 7.25 to 8.42) preop and 7.95 ± 0.31 mm (range 7.39 to 8.74) after removal of the epithelium (P < 0.0001). The mean Sim K’s astigmatism increased from 0.84 ± 0.97 D (range 0 to 4.7) preop to 1.37 ± 0.95D (range 0.2 to 4.6) after removal of the epithelium (P < 0.0001). The mean irregularity index increased from 1.10 ± 0.39 D (range 0.5 to 2.3) to 2.04 ± 0.40D (range 1.3 to 3.1) (P < 0.0001). The mean asphericity (Q) changed from –0.43 ± 0.14 (range –0.72 to –0.23) before to –0.69 ± 0.51 (range –2.85 to 0.12) after epithelium removal (P = 0.003).
The epithelium affects the topographic properties of the cornea as it significantly reduces the corneal topographic astigmatism and irregularity. This might prove to be important in the assessment of candidacy and treatment planning in refractive surgery.
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