Medial canthus single-injection episcleral (sub-tenon anesthesia): Computed tomography imaging

Single-injection medial canthus periocular anesthesia is a promising regional anesthesia technique for ophthalmic surgery. The purpose of this computed tomography (CT) study was to confirm that this technique is an episcleral injection and to explain why it provides a good akinesia of the globe. Four fresh nonpreserved cadavers (eight eyes) were injected with fractioned various volumes of a contrast media using a previously described technique. For each injection and each eye, CT scans were performed in three planes of the space, and the site and spread of the injection was observed. We confirm that single-injection medial canthus periocular anesthesia is, in fact, an episcleral anesthesia, which explains the good sensory block of the globe. When larger volumes are injected, the contrast media spreads to the lids and extraocular muscle sheaths. We believe that this may explain why this technique provides good sensory and motor block of the globe and eyelids. This technique is a promising alternative to both retro- and peribulbar anesthesia. Implications: We describe medial canthus single-injection periocular anesthesia by a computed tomography injection study in eight human cadaver eyes. It was confirmed to be an episcleral injection. Akinesia of the eyeball is provided by spreading of the local anesthetic solution from the episcleral space to the rectus muscle sheaths.