PURPOSE‏:‏This is a randomized controlled study aiming to evaluate the safety and efficacy of two ‎different concentrations of topical nalbuphine hydrochloride, when used to relieve pain in the first days ‎following photorefractive keratectomy (PRK). ‎ METHODS ‎‏ :‏This is a prospective double blinded randomized clinical trial that included 189 patients who ‎had PRK for correction of low and moderate refractive errors. Patients were randomly assigned to three ‎groups according to the eye drops given to relieve pain in the first three postoperative days; the first group ‎received topical nalbuphine with a concentration of 2 mg/ml (Group A = 64 patients), the second group ‎received topical nalbuphine in a concentration of 1 mg/ml (Group B = 69 patients) and the third group ‎received topical artificial tears only (Group C = 56 patients).The patients were asked to rate their pain daily ‎using a numeric rating scale and to record the number of drops instillation times/day. The time needed for ‎complete epithelial healing, best-corrected visual acuity (BCVA) and spherical equivalent after three ‎months were recorded in each group.‎ ‎ RESULTS‏:‏‎ In the first three days, there was a statistically significant difference in pain score among the ‎three groups with lower values in the two topical nalbuphine groups when compared with the control group ‎receiving artificial tears. Moreover, the higher concentration group showed significantly lower pain score ‎and less number of drops used /day in comparison with the lower concentration group.‎‏ ‏There were no ‎statistically significant differences in epithelial healing time, BCVA and spherical equivalent after three ‎months among the three groups. ‎ CONCLUSION‏:‏‎ The use of topical nalbuphine is effective in relieving pain in the first few days following ‎PRK and this pain relief is not associated with any compromise regarding epithelial healing nor refractive ‎outcome. The pain control with 2 mg/ml concentration is significantly higher than that with 1 mg/ml ‎concentration of nalbuphine. ‎