RESEARCH SUPPORT, NON-U.S. GOV'T
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Excimer laser in situ keratomileusis and photorefractive keratectomy for correction of high myopia.

BACKGROUND: The purpose of this research was to study the visual outcome of excimer laser photorefractive keratectomy and laser in situ keratomileusis (LASIK) for the correction of moderate and high myopia.

METHODS: Twenty partially-sighted eyes of 20 patients were divided into two groups, LASIK and photorefractive keratectomy. Ten eyes underwent LASIK and the other 10 photorefractive keratectomy. Follow up was at 1, 3, 6, and 12 months. The LASIK technique included a nasally based, 150 microns thick, 8.0 x 9.0 mm diameter, truncated, disc-shaped corneal flap created with a microkeratome; and the ablation of the stroma with a 193-nanometer ArF excimer laser. The flap was returned to its original position and held in place by apposition. The photorefractive keratectomy technique included mechanical removal of the epithelium and ablation of the stroma with a 193-nanometer ArF excimer laser.

RESULTS: LASIK series: One eye had a ruptured globe during the second postoperative month and was excluded from the study. The preoperative spherical equivalent refraction ranged from -10.62 to -25.87 diopters (D). The attempted correction ranged from -8.00 to -16.00 D. Postoperative refraction and corneal topography stabilized between 4 and 12 weeks. Spectacle-corrected visual acuity was within 1 Snellen line of preoperative in all eyes. The refraction in six eyes (66.6%) was within +/- 1.00 D of the intended correction, and in eight eyes was within +/- 2.00 D (88.8%) at 12 months. The mean attempted correction (11.40 +/- 2.60 D) was close to the mean achieved correction at 12 months (11.96 +/- 3.10 D). The mean postoperative refractive astigmatism (1.50 +/- 0.97; range, 0.25 to 3.50 D) was close to the preoperative astigmatism (1.70 +/- 1.15; range, 0 to 3.75 D). Endothelial cell density at 12 months showed an average 8.67% of cell loss. All eyes showed a clear interface. Photorefractive keratectomy series: The preoperative spherical equivalent refraction ranged from -10.75 to -23.12 D. The attempted correction ranged from -8.80 to -17.60 D. Postoperative refraction showed regression throughout the follow-up period, and corneal topography did not stabilize. Spectacle-corrected visual acuity was within 1 Snellen line in eight eyes. Two eyes lost 2 and 3 Snellen lines. One eye was within +/- 1.00 D, and three eyes (30%) were within +/- 2.00 D of the intended correction at 12 months. The achieved correction mean (7.17 +/- 5.29 D) was 61% of the attempted mean (11.72 +/- 2.81 D) at 12 months. The postoperative refractive astigmatism (1.80 +/- 0.95; range, 0.50 to 4.00 D) was very close to the preoperative (1.90 +/- 1.33; range, 0 to 5.00 D). Endothelial cell density showed an average of 10.56% cell loss at 12 months. The mean haze at 12 months was 1.2 (0 to 4 scale).

CONCLUSION: LASIK, although more complicated because of the use of a microkeratome, was more effective than photorefractive keratectomy in higher myopes. LASIK created less corneal haze. The refraction was more stable with LASIK in the correction of high myopia. Its predictability was three times that of PRK.

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