EXCIMER-LASER IN-SITU KERATOMILEUSIS AND PHOTOREFRACTIVE KERATECTOMY FOR CORRECTION OF HIGH MYOPIA

BACKGROUND: The purpose of this research was to study the visual outco me of excimer laser photorefractive keratectomy and laser in situ kera tomileusis (LASIK) for the correction of moderate and high myopia. MET HODS: Twenty partially-sighted eyes of 20 patients were divided into t wo groups, LASIK and photorefractive keratectomy. Ten eyes underwent L ASIK and the other 10 photorefractive keratectomy. Follow up was at 1, 3, 6, and 12 months. The LASIK technique included a nasally based, 15 0 mum thick, 8.0 x 9.0 mm diameter, truncated, disc-shaped corneal fla p 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 keratec tomy technique included mechanical removal of the epithelium and ablat ion of the stroma with a 193-nanometer ArF excimer laser. RESULTS: LAS IK series: One eye had a ruptured globe during the second postoperativ e month and was excluded from the study. The preoperative spherical eq uivalent refraction ranged from - 10.62 to -25.87 diopters (D). The at tempted correction ranged from -8.00 to -16.00 D. Postoperative refrac tion and corneal topography stabilized between 4 and 12 weeks. Spectac le-corrected visual acuity was within 1 Snellen line of preoperative i n all eyes. The refraction in six eyes (66.6%) was within +/- 1.00 D o f 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) wa s 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 showe d an average 8.67% of cell loss. All eyes showed a clear interface. Ph otorefractive keratectomy series: The preoperative spherical equivalen t refraction ranged from -10.75 to -23.12 D. The attempted correction ranged from -8.80 to -17.60 D. Postoperative refraction showed regress ion throughout the followup period, and corneal topography did not sta bilize. 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). CONC LUSION: LASIK, although more complicated because of the use of a micro keratome, was more effective than photorefractive keratectomy in highe r myopes. LASIK created less corneal haze. The refraction was more sta ble with LASIK in the correction of high myopia. Its predictability wa s three times that of PRK.