Peribulbar versus retrobulbar anesthesia for ophthalmic surgery - An anatomical comparison of extraconal and intraconal injections

Background: Peribulbar and retrobulbar anesthesia have long been opposed on the basis of the existence of an intermuscular membrane, which is supposed to separate the intraconal from the extraconal spaces in a water-tight fas hion. A local anesthetic injected outside the cone should spread through th is septum to reach the nerves to be blocked. The existence of this septum i s questioned. The aim of this study was to compare the spread of a colored latex dye injected intraconally or extraconally to simulate both retrobulba r and peribulbar anesthesia. Methods: The authors used 10 heads from human cadavers. For each head, one eye was injected intraconally, and the other eye was injected extraconally. The heads were then frozen and sectioned into thin slices following variou s planes. They were then photographed and observed. Results: There was no evidence of the existence of an intermuscular septum separating the intraconal and extraconal spaces. Those two spaces appeared to be part of a common spreading space, the corpus adiposum of the orbit. Conclusions: These results are in accord with the fact that clinical studie s were not able to clearly demonstrate that retrobulbar anesthesia is more efficient than peribulbar anesthesia. On the basis of a similar clinical ef ficacy of the two techniques as a result of similar spreading of the local anesthetic injected, and a potentially higher risk of introducing the needl e into the muscular cone, the authors recommend replacing retrobulbar anest hesia with peribulbar anesthesia.