Advanced Surface Ablation-Photorefractive Keratectomy (ASA-PRK): Safety and Clinical Outcome for the Correction of Mild to Moderate Myopia with a Thin Cornea

Lee, Sang Bumm; Chung, Min Su

Abstract

PURPOSE: To evaluate the safety, clinical outcome, and change in higher-order wavefront aberrations (HOAs) of Advanced Surface Ablation-Photorefractive Keratectomy (ASA-PRK) for the correction of mild to moderate myopia in cases with a thin cornea.
METHODS
ASA-PRK was performed, using a rotary epithelial scrubber, post-laser chilled BSS(R) irrigation, and bandage contact lens, in 127 eyes of 70 patients who had a preoperative spherical equivalent within -7.0 D and who were followed-up for more than six months. The patients were divided into two groups, according to their central corneal thickness (CCT), by ultrasonic pachymetry (Group: CCT< or =520 micrometer, 32 eyes, mean 506.6+/-8.6 micrometer; Group: CCT>520 micrometer, 95 eyes, mean 552.3+/-24.8 micrometer). The clinical outcomes of Group I and II were compared.
RESULTS
At six months, 100% of Group I (32/32 eyes) and 93.7% of Group II (89/95 eyes) had an UCVA of 1.0 or better (p>0.05). At six months, a spherical equivalent within 0.5 D of emmetropia was observed in 100% (32/32) of the eyes in Group I and in 94.7% (90/95) of the eyes in Group II (p>0.05). At the 12-month follow-up, all eyes showed good stability of the refractive errors, and none showed corneal haze of grade 1 or more, loss of two or more lines of BSCVA, or serious iatrogenic keratectasia. The magnitude of total HOAs, spherical ablation, and coma were significantly higher six and 12 months after surgery in both groups (p<0.05). The postoperative changes in the HOAs at six and 12 months were similar in both groups (p>0.05).
CONCLUSIONS
ASA-PRK performed on patients with mild to moderate myopia and a thin cornea (> or =490 micrometer) showed a high level of efficacy, predictability, stability, and safety. There was no statistically significant difference in surgically induced HOAs between Groups I and II. The authors suggest that ASA-PRK be used for the correction of mild to moderate myopia, especially in cases with a thin cornea. Further study will be needed to determine the safety of this procedure for thinner corneas in surface keratorefractive surgery.