Effect of volume used in sub-Tenon's anaesthesia on efficacy and intraocular pressure: a randomized clinical trial of 3 mL versus 5 mL

PURPOSE: To compare the effect of volume used in sub-Tenon's anaesthesia on efficacy and intraocular pressure (IOP). METHODS: A prospective, randomised clinical trial was conducted on 52 eyes of 52 consecutive patients undergoing sub-Tenon's anaesthetic for cataract surgery. Eyes were randomly assigned to either 3 mL or 5 mL volume of anaesthetic solution (0.5% bupivacaine/2% lidocaine in a 50:50 mixture). The main outcome measures were akinesia 5 min post-administration of anaesthetic, changes in IOP immediately after and 5 min after anaesthetic administration, and patient pain perception during procedure. RESULTS: The level of kinesia was greater in the 3 mL group (n = 25) compared to the 5 mL group (n = 27) (P = 0.001, Mann-;Whitney U-test). There was no significant difference in pain perception between the two groups (P = 0.464, student t-test). Although there was great variation in IOP changes following sub-Tenon's anaesthetic, there was a trend for a larger rise in mean IOP immediately after anaesthetic administration in the 5 mL group (mean +/- SD +5.6 +/- 4.2 mmHg) compared to the 3 mL group (+4.3 +/- 3.8 mmHg), but this did not reach statistical significance (P = 0.25, student t-test). CONCLUSIONS: A 5 mL volume of anaesthetic provides akinesia superior to a 3 mL volume in sub-Tenon's anaesthesia for cataract surgery.