Nine-Year Results of Excimer Laser Photorefractive Keratectomy for Myopia

ABSTRACT

PURPOSE: To evaluate the long term stability, complications, and causative factors in eyes that had photorefractive keratectomy (PRK) for myopia. METHODS: We investigated the results of photorefractive keratectomy (PRK) on 72 consecutive myopic eyes (45 patients) with follow-up of 9 years by using Eximed UV 200LA laser (Summit technology, USA). The patients were divided into two groups according to preoperative myopia group 1 with diopters between -3.25 D and -6.50 D, group 2 with diopters above -6.50 D. During the follow-up period, 1, 2, 3, 5, 7 and 9 years, refractive error, uncorrected and best corrected visual acuity and corneal opacity were examined. Preoperative myopia ranged from -3.25 D to -9.12 diopters (D), with astigmatism of less than 1.50 D. The excimer laser was set to a maximum correction of -6.50 D at a 5.0mm diameter ablation zone. Patients with more than -6.50 Dmm of myopia had double-pass PRK with two different ablation zone sizes (5.0 and 4.5 mm). The data were analyzed using paird T-test and Regression analysis. RESULTS: Mean refractive error 9 years after PRK was -2.10+/-0.99 D. It was -1.67+/-0.71 D in moderately myopic eyes (less than 6.50 D) and -2.60+/-1.04 D in highly myopic eyes (more than 7.0 D). The Myopic regression rate markedly decreased after 2years in moderate myopic group but after 3 years in highly myopic group (P<0.01). The most possible causative factor for myopic regression were pre-PRK refraction (P<0.01) and its relative risk was 4.21 At 9 years, 92.3% eyes achieved uncorrected visual acuity of 0.5 or better group1, and 78.7% in group2. Moderate corneal haze was present in 2eyes in group 2. CONCLUSION: According to these results, we thought that eximer PRK was effective for myopia under -9.62 D. Myopic regression was stabilized after 3 years of PRK.