Comparison of retrobulbar and periocular injections of lignocaine by computerised tomography.

Ten patients undergoing cataract surgery were given a local anaesthetic with lignocaine solution which was mixed with iohexol contrast medium. The location of the needle and the substance injected was determined by computerised tomography following retrobulbar or periocular anaesthesia. The retrobulbarly inserted needles were within the muscle cone, directed towards the optic foramen. The periocular needles were outside the muscle cone, tangentially along the orbital floor or pointing slightly upwards. After the retrobulbar injection the contrast medium was seen within the cone immediately after the injection and outside the cone as early as 3 minutes after the injection. With the periocular technique, however, diffusion of the anaesthetic in the opposite direction (that is, into the muscle cone) was rapid. The contrast medium was identified inside the muscle cone 2 minutes after the injection. Compression with an intraocular pressure reduction device after both of these techniques prevented exophthalmos. It is concluded that retrobulbar-like anaesthesia can also be induced by an appropriate periocular technique.