Photorefractive keratectomy (PRK) is a kind of refractive error surgery with a long history in refractive error corrections. There are several ways for epithelial debridement before stromal ablation. In this study, we compared clinical factors such as operation time, rate of re epithelialization, postoperative pain, refractive error, epithelial defect, intraocular pressure, contrast acuity, uncorrected and best corrected acuity in mechanical (m-PRK) and trans epithelial PRK (t-PRK). This comparative study included 80 eyes of 40 patients with myopia and mean age of 31.22+-8.7 (ranged from 20 to 55) years. After complete preoperative examinations, mechanical technique was done in one eye randomly and transepithelial technique in the contralateral eye. All postoperative clinical factors were measured and recorded in 6 months. The inclusion criteria was patients with myopia up to 8.00D and have trend for doing PRk, with normal corneal thickness, normal IOP, normal epithelium and endothelium, and… the exclusion criteria was patients with anterior or posterior segment pathology, progressive refractive error, keratoconus, history of any ocular surgery and…