Background Total volume using a standard single inferonasal injection for sub-Tenon's anaesthesia is limited by an increase in intraocular pressure (IOP) and commonly requires the operating surgeon to top-up the block intraoperatively. This study compares the efficacy and safety of a two-quadrant technique that allows the use of a higher volume of local anaesthetic.

Methods 54 patients undergoing vitrectomy were randomised into two groups. The control group (n=27) received a standard 5 ml single inferonasal sub-Tenon injection of a 50:50 mixture of 2% lidocaine and 0.5% bupivacaine with 150 IU hyaluronidase. The study group (n=27) received a 5 ml inferonasal and 5 ml superotemporal injection of the same mixture (10 ml total). The primary outcome measure was the number of intraoperative top-ups required. Secondary outcome measures were intraoperative and postoperative pain scores, IOP, block onset time, ocular akinesia, eyelid akinesia and chemosis.

Results 24 patients required a top-up in the control group. No patients required a top-up in the study group (p<0.001). IOP measurements were similar in both groups. Block onset was shorter, eyelid akinesia was improved and pain scores were also reduced in the study group intraoperatively and at 0–2 h, 4–6 h, 10–14 h and 20–24 h postoperatively.

Conclusions Two-quadrant sub-Tenon's anaesthesia using 10 ml of a 50:50 mixture of 2% lidocaine and 0.5% bupivacaine with 150 IU hyaluronidase seems to be more effective than a single-quadrant technique at reducing intraoperative and postoperative pain during vitrectomy.