AIM: To investigate the effect of hyaluronidase use on the quality of sub-Tenon's anesthesia for phacoemulsification.METHODS: This was a randomized, double-blind clinical trial which was conducted at Nikookari Eye Hospital for 5 months. Forty-two eyes of candidates for phacoemulsification under sub-Tenon's anesthesia were randomly allocated to two equal groups and received either 2mL of lidocaine 2% solution with (LH), or without (L) addition of hyaluronidase (150U/mL). Akinesia was assessed 15 minutes after sub-Tenon's injection. Patients and surgeon's satisfaction, as well as the postoperative pain (the visual analogue scale, VAS) were investigated after operation. The contingency tables (including the Chi-square or Fisher's exact tests, when appropriate) and parametric analysis (the independent samples ttest) were used for statistical analysis.RESULTS: Complete akinesia (33.3% vs4.8%, P=0.04), as well as the patients (85.7% vs57.1%, P=0.04) and surgeon's satisfaction (87.5% vs52.4%, P=0.02) were significantly more frequent in LH than in L group. The mean VAS was significantly lower in the same group (1.90±1.45 vs3.00±1.55, P=0.04).CONCLUSION: Addition of hyaluronidase to lidocaine solution for sub-Tenon's anesthesia significantly improves the ocular akinesia, enhances the intra-operative patients and surgeons' satisfaction, and attenuates the postoperative pain.