Magnetic resonance image changes following optic nerve trauma from peribulbar anaesthetic

E ditor ,-In this case a grand mal seizure occurred after a short peribulbar anaesthetic needle was used, permanent visual loss resulted, and magnetic resonance imaging (MRI) confirmed optic nerve damage. COMMENT Peribulbar anaesthesia has been advocated as a safer technique than retrobulbar anaesthesia as the risk of optic nerve damage is significantly less. 1 Injection of anaesthetic in the optic nerve sheath can cause brainstem anaesthesia and is well described with retrobulbar blockade. 2-5 The risk of brainstem anaesthesia increases with the length of needle used, and if the eye is in the Atkinson position. 1 2 5 Even with planned peribulbar block it has been estimated that an intraconal anaesthetic has been given in 1.3% of cases. 1 Direct trauma to the optic nerve can occur after orbital block, characteristically without associated brainstem anaesthesia. 6 7 The visual loss may be associated with signs of a retinal artery occlusion, 8 subhyaloid haemorrhage, 7 or a retinal vein occlusion. 9 In some of these cases the optic nerve sheath swelling was confirmed by ultrasonography or CT, and intraneural sheath haemorrhage was treated in one case by optic nerve sheath decompression with limited visual improvement. 9 Prilocaine (Citanest) was used as the anaesthetic agent; it is similar to lignocaine, and has the advantage of being 50% less toxic, with reduced local irritation and slower systemic absorption. 10 Contraindications include anaemia and at high concentrations it can cause methaemoglobinaemia.