The paper by Farmery and colleagues  has eloquently demonstrated the benefits that accrue from performing a sub-Tenon block in patients who are undergoing general anaesthesia for vitreo-retinal procedures. Their study did not address the question of whether general anaesthesia itself is necessary.
Sub-Tenon blocks are known to provide effective anaesthesia of the orbit and contents for several hours [2-5]. Although many surgeons prefer general anaesthesia for vitreo-retinal procedures, this is by no means universal. A recent audit showed that more than 250 vitreo-retinal procedures were performed during the course of a year at our hospital. Of these, 22% were performed under general anaesthesia. In the remaining patients the procedures were performed under sub-Tenon block. None of the latter patients required intraoperative sedation or systemic analgesia. Most operations were completed within, or soon after, an hour and there did not appear to be any difference in surgical outcome when compared with those patients undergoing general anaesthesia and a local block.
We believe that a randomized, controlled trial is now required to definitively determine whether or not general anaesthesia is required in addition to a sub-Tenon block for vitreo-retinal procedures that can be performed within an hour.
*Departments of Anaesthesia and Ophthalmology, Norfolk and Norwich University Hospital, Norwich, UK
1. Farmery AD, Shlugman D, Rhaman R, Rosen P. Sub-Tenon's block reduces both intraoperative and postoperative analgesia requirements in vitreo-retinal surgery under general anaesthesia. Eur J Anaesthiol
2. Canavan KS, Dark A, Garrioch MA. Sub-Tenon's administration of local anaesthetic: a review of the technique. Br J Anaesthiol
3. Guise PA. Sub-Tenon anesthesia: a prospective study of 6,000 blocks. Anesthesiology
4. Calenda E, Olle P, Muraine M, Brasseur G. Peribulbar anesthesia and sub-Tenon injection for vitreoretinal surgery: 300 cases. Acta Ophthalmol Scand
5. Sharma T, Gopal L, Parikh S, Shanmugam MP, Badrinath SS, Mukesh BN. Parabulbar anesthesia for primary vitreoretinal surgery. Ophthalmology