Evaluation of the Greenbaum sub-Tenon's block.

A prospective, randomized blind study was conducted in 40 patients undergoing phacoemulsification and posterior chamber intraocular lens implantation. They received anaesthetic infiltration of 2% lidocaine with 1:200,000 epinephrine and hyaluronidase 150 U ml(-1) in a volume of 2, 3, 4 or 5 ml into the sub-Tenon's fascial space through a Greenbaum cannula after a conjunctival incision. Reduction of ocular movements, anaesthesia, pain on injection and any incidental complications were recorded. Akinesia and anaesthesia occurred within 5 min with 4 and 5 ml of local anaesthetic, and no supplementary injections were required. There were marked reductions in the frequency of forced eyelid movements with these volumes. Chemosis and conjunctival haemorrhage were noted in the majority of patients but caused no intraoperative problems. Approximately 10-15% of patients reported slight discomfort at the time of injection. Four to 5 ml of 2% lidocaine with 1:200,000 epinephrine and 150 U ml(-1) of hyaluronidase is the optimum volume to achieve adequate akinesia, anaesthesia and reduction of lid movements during the Greenbaum sub-Tenon's block.