COMPARISON OF 5-MM AND 6-MM ABLATION ZONES IN PHOTOREFRACTIVE KERATECTOMY FOR MYOPIA

BACKGROUND: Variation in ablation zone diameter may alter visual acuit y and/or refractive effect in photorefractive keratectomy. Despite the oretical benefits of using a smaller diameter ablation zone, clinical studies suggest that a larger ablation zone may decrease problems asso ciated with photorefractive keratectomy. METHODS: The results of our i nitial 34 consecutive eyes treated with a 5-mm diameter ablation zone using a Summit Technology ExciMed UV200LA excimer laser were compared retrospectively to our initial 34 consecutive eyes treated with a 6-mm diameter ablation zone using a Summit OmniMed excimer laser. Eyes had a spherical equivalent refraction between -1.00 and -6.00 diopters (D ) and astigmatism less than 1.00 D. Patients were followed for a minim um of 6 months. RESULTS: Eyes treated with a 6-mm ablation zone had le ss hyperopia and a spherical equivalent refraction closer to emmetropi a at 1, 2, and 3 months (P=0.001). Eyes treated with a 6-mm ablation z one had better uncorrected visual acuity at 1 and 2 months (P=0.001). Less subepithelial haze was noted at 2 months (P=0.01) and 3 months (P =0.002) in the 6-mm group. At 6 months postoperatively, 30 of 32 eyes (94%) treated with a 6-mm ablation zone had a spherical equivalent ref raction within 0.50 D of emmetropia, and all 32 eyes (100%) were withi n 1.00 D of emmetropia; in the 5-mm ablation zone group, 28 of 34 eyes (80%) were within 0.50 D and 29 (85%) were within 1.00 D of emmetropi a. Patients treated with a 6-mm ablation zone complained less of night halos and had fewer differences between night and day vision. CONCLUS IONS: In this study of myopia of -1.00 D to -6.00 D, eyes treated with a 6-mm ablation zone achieve a more rapid visual recovery with less v ariation in refractive outcome and less adverse effects than those tre ated with a 5-mm ablation zone.