This complication is probably related more to injection technique than to the presence or absence of hyaluronidase, but it occurs in the hands of even the most experienced surgeons, and hyaluronidase may provide a safety margin. The best evidence suggests that intramuscular injection of the anesthetic is the culprit. Perhaps hyaluronidase speeds diffusion of the anesthetic from the muscle tissue. Sub-Tenon infusion of anesthetic with a blunt cannula is a good alternative to retrobulbar or peribulbar blocks. In older individuals, Tenon s capsule is thin, providing little barrier to posterior diffusion of the anesthetic.
Pain relief is excellent, and akinesia is usually good.
Care should probably be taken not to inject the anesthetic against resistance to avoid creating a loculated cyst of anesthetic, the pressure from which was probably responsible for the one case of central retinal artery occlusion I have seen with this technique. In other words, pull back slightly if the anesthetic does not flow freely from the tip of the blunt cannula. An added and welcome advantage of sub-Tenon infusion is avoidance of retrobulbar hemorrhage. Anterior segment surgeons who prefer injection anesthesia suggest that the onset of anesthesia is more rapid and that excess orbital pressure dissipates quickly when the agent is added to the anesthetic mixture. Moreover, there has been concern regarding an increased incidence of postoperative diplopia when Wydase has been unavailable.