MEDIAL CANTHUS EPISCLERAL (SUB-TENON) ANESTHESIA IMAGING

Medial canthus single injection periocular anesthesia is an alternativ e technique to classical regional anesthesia techniques for cataract s urgery. The occurrence of a chemosis at the end of this injection has made us question ourselves about the real site of injection. The purpo se of this anatomic study was to identify this site with precision, an d to describe the spreading of the injected solution. Various volumes of colored liquid latex were injected when using this technique on 10 human orbits. They were deeply frozen and sectioned in thin slices. Th e site of injection is clearly the episceral (sub-Tenon) space. This i s a gliding space through which pass the ciliary nerves supplying the globe sensitivity. This could explain the high quality of the analgesi a of the globe. With the larger volumes injected, spreading of the lat ex was detected in the orbicularis palpebra. This probably explains th e good akinesia of the lids obtained without any facial block. Spreadi ng of the latex to the rectus muscles sheaths should explain the good akinesia of the globe, but was only partially proved in this study. We conclude that the medial canthus single injection periocular anesthes ia is an episcleral (sub-Tenon) injection which may explain good anest hesia. (C) 1998 Wiley-Liss. Inc.