Bckground:This study was designed to evaluate the efficacy, safety and complications of Photorefractive keratectomy (PRK) as a retreatment of residual myopia after previous laser insitu keratomileusis (LASIK).
Methods:In this descriptive study, with the consideration of inclusion and exclusion criteria, the 92 cases were selected and underwent PRK with mitomycin C.
Findings: This study was performed on 170 eyes of 92 patients with the mean age of 35 years old (56 women and 36 men). The average interval between two procedures was 17.5 ± 3.2 months. After 1 year, 94.7% of the eyes had uncorrected visual acuity (UCVA) (20/40 or better) and 65.8% of eyes had UCVA (20/20 or better). 135 eyes (79.4%) were within ± 0.5 diopter (D) and 168 eyes (98.8 %) were within ± 1.00 D of target refraction. 2 eyes lost one line of best corrected visual acuity (BCVA) and 14 eyes had BCVA gain. After 12 months four eyes had corneal haze of grade 2. Before and after PRK, Spheric equivalents of eyes were
-1.84 ± 0.6 and -0.15 ± 0.2 D respectively (P < 0.001), mean UCVA was 0.34 ± 0.23 and 0.92 ± 0.14 of lines (P < 0.001) and the mean pachymetry was 428 ± 20 and 407 ± 12 microns respectively (P = 0.032).
Conclusion:PRK is an effective and safe procedure as a retreatment of post LASIK residual myopia.

Key words:LASIK, Photorefractive keratectomy (PRK), Retreatment, Myopia.