Hyaluronidase permits a significant 2.4-fold (95% CI, 1.8-3.4) reduction in MLAV for sub-Tenon's anaesthesia.

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seem, therefore, that this technique would be detrimental to patients. However, when undertaken under controlled conditions for short periods of time (usually 2-3 h) and followed by careful resuscitation, it has produced, in our unit, excellent results in terms of minimal liver dysfunction, blood transfusion requirements and mortality. Volumes of local anaesthetic for sub-Tenon's anaesthesia vary between 2 ml and 11 ml. Lower volumes produce less akinesia, whilst higher volumes increase chemosis and intra-ocular pressures [1]. This randomised, blinded, sequential allocation study examined the effect of adding hyaluronidase on the minimum local anaesthetic volume (MLAV) required for a sub-Tenon's block, in patients having cataract extractions. MethodsFollowing Local Research Ethics Committee and Medicines and Healthcare products Regulatory Agency approval, 62 patients having sub-Tenon's blocks for cataract surgery were randomly assigned to two groups. The control group (n ¼ 31) received plain lidocaine 2% and the study group (n ¼ 31) received lidocaine 2% with 15 iu.mlhyaluronidase. Using parallel up-down sequential allocation, from a 4-ml starting point, the volumes in both groups changed by 1 ml according to the quality of globe akinesia, as judged by a blinded researcher using a standardised scoring system. The MLAV was calculated for both groups using Dixon and Massey formulae. Student's t-tests were used to compare the groups. ResultsThe groups were similar for age, sex and axial length. There was a difference in MLAV of 3.0 ml ( Fig. 1; control: 5.9 ml (95%CI 4.3-7.9 ml); hyaluronidase: 2.9 ml (95% CI 2.4-3.5 ml); p < 0.001). The hyaluronidase group showed less variability (p < 0.01).