Photorefractive Keratectomy (PRK) is Safe and Effective for Patients with Myopia and Thin Corneas

Abstract The aim of this study was to evaluate the long-term safety and efficacy of photorefractive keratectomy (PRK) for patients with myopia and thin corneas. In this retrospective case series, we included ۷۴ eyes of ۳۸ patients with myopia and central corneal thickness (CCT) < ۵۵۰ µm who underwent PRK and had a mean postoperative follow-up period of four years. The following factors were evaluated: CCT, refraction, uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), ablation depth, safety and efficacy indices (i.e., the ratio of the mean postoperative BCVA to the mean preoperative BCVA, and the ratio of the mean postoperative UCVA to mean preoperative the BCVA, respectively), and evidence of corneal ectasia (based on Orbscan topography images).The patients were aged ۲۰ – ۴۶ years (mean ±SD age, ۲۸.۱۸± ۶.۸۲ years). The mean ± SD pre- and postoperative CCTwas۴۸۵.۹۲ ± ۹.۲۷ µm and ۴۳۴.۸۴ ± ۲۰.۴۸ µm, respectively. The mean ± SD pre- and postoperative myopia was -۲.۷۷ D ± ۱.۵۱ and -۰.۲۴ ± ۰.۳۹ D, respectively, and the mean ± SD pre- and postoperative astigmatism was -۰.۸۲ D ± ۰.۹۹ and -۰.۳۷ ± ۰.۳۷ D, respectively. The mean pre- and postoperative BCVA and postoperative UCVA was ۰.۰۱۱ ± ۰.۰۳ Logarithm of the Minimum Angle of Resolution (log MAR), ۰.۰۰۳ ± ۰.۰۱ log MAR, and ۰.۰۵۴ ± ۰.۰۹ log MAR, respectively. The mean ± SD ablation depth, safety index and efficacy index was ۵۴.۳۴ ± ۱۶.۲۸ µm, ۰.۰۲ ± ۰.۱۲, and ۰.۱۱ ± ۰.۵۰, respectively. Regarding the postoperative corneal clarity, ۷۲ eyes (۹۷.۳%) had a clear cornea (grade ۰) and the remaining two eyes of one patient (۲.۷۰%) had a trace haze (grade ۱). There was no evidence of corneal ectasia on any of the Orbscan topography images. Thus, among patients with myopia and thin corneas (<۵۰۰ µm), PRK seems to be acceptable in terms of both safety and efficacy ۴ years after surgery, based on the stability of postoperative refraction, visual acuity, and topographic outcomes, and outcomes based on the safety and efficacy indexes.Â