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  • Title: Comparison of corneal wavefront aberrations after photorefractive keratectomy and laser in situ keratomileusis.
    Author: Oshika T, Klyce SD, Applegate RA, Howland HC, El Danasoury MA.
    Journal: Am J Ophthalmol; 1999 Jan; 127(1):1-7. PubMed ID: 9932992.
    Abstract:
    PURPOSE: To compare changes in the corneal wavefront aberrations after photorefractive keratectomy and laser in situ keratomileusis. METHODS: In a prospective randomized study, 22 patients with bilateral myopia received photorefractive keratectomy on one eye and laser in situ keratomileusis on the other eye. The procedure assigned to each eye and the sequence of surgery for each patient were randomized. Corneal topography measurements were performed preoperatively, 2 and 6 weeks, 3, 6, and 12 months after surgery. The data were used to calculate the wavefront aberrations of the cornea for both small (3-mm) and large (7-mm) pupils. RESULTS: Both photorefractive keratectomy and laser in situ keratomileusis significantly increased the total wavefront aberrations for 3- and 7-mm pupils, and values did not return to the preoperative level throughout the 12-month follow-up period. For a 3-mm pupil, there was no statistically significant difference between photorefractive keratectomy and laser in situ keratomileusis at any postoperative point. For a 7-mm pupil, the post-laser in situ keratomileusis eyes exhibited significantly larger total aberrations than the post-photorefractive keratectomy eyes, where a significant intergroup difference was observed for spherical-like aberration, but not for coma-like aberration. This discrepancy seemed to be attributable to the smaller transition zone of the laser ablation in the laser in situ keratomileusis procedure. Before surgery, simulated pupillary dilation from 3 to 7 mm caused a five- to six-fold increase in the total aberrations. After surgery, the same dilation resulted in a 25- to 32-fold increase in the photorefractive keratectomy group and a 28- to 46-fold increase in the laser in situ keratomileusis group. For a 3-mm pupil, the proportion of coma-like aberration increased after both photorefractive keratectomy and laser in situ keratomileusis. For a 7-mm pupil, coma-like aberration was dominant before surgery, but spherical-like aberration became dominant postoperatively. CONCLUSIONS: Both photorefractive keratectomy and laser in situ keratomileusis increase the wavefront aberrations of the cornea and change the relative contribution of coma- and spherical-like aberrations. For a large pupil, laser in situ keratomileusis induces more spherical aberrations than photorefractive keratectomy. This finding could be attributable to the smaller transition zone of the laser ablation in the laser in situ keratomileusis procedure.
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