Effect of Volume Used in Sub-Tenon’s Anesthesia on Efficacy and Intraocular Pressure in Vitreoretinal Surgery

PURPOSE: To compare the effect of volumes used in sub- Tenon's anesthesia on efficacy and intraocular pressure (IOP) in vitreoretinal surgery. METHODS: A prospective clinical trial was conducted on patients undergoing sub-Tenon's anesthesia for vitreoretinal surgery. Patients were randomized to receive either 3-, 5- or 7-ml volumes of anesthetic solution. IOP were measured immediately prior to injection, immediately after injection and at 2, 5 and 10 min after injection. Pain scores were assigned using a numerical visual analogue scale immediately after surgery, and again on postoperative day 1. RESULTS: A total of 108 patients (119 eyes) were studied, including 35 eyes in the 3-ml group, 48 eyes in the 5-ml group, and 36 eyes in the 7-ml group. There were significant elevations in mean IOP following injection in all groups, and a trend for larger rises in IOP with larger volumes of anesthesia (p < 0.01). Mean IOP were elevated after injection, and reduced at all time intervals. However, the reduction in the 3-ml group took levels to preinjection amounts. There were no significant differences in patient-reported pain scores among the groups when assessed immediately after surgery or on postoperative day 1. The incidence of chemosis and high IOP elevations (>or=40 mm Hg) were more frequent in the 7-ml group (p < 0.05). CONCLUSIONS: Sub-Tenon's anesthesia is effective in vitreoretinal surgery. It would appear that a 3-5-ml volume of anesthetic is safe, when considering the associated complications.