Anaesthesia for Ophthalmic Surgery: How "Retro" is the Peribulbar Block?

Ophthalmic surgery on the posterior section of the eye can either be performed under general anaesthesia or under local aneasthesia. The local anaesthesia is performed by injecting local anaesthetics behind the eye. There are two techniques: Either the needle is placed into the muscle cone formed by the four recti muscles - this is called intraconal or retrobulbar block, or the needle is placed outside of the muscle cone - this would be called extraconal or peribulbar. In our hospital the investigators usually perform the peribulbar block since it is easier to perform and has a smaller risk to injure the eye. The investigators however realize that the parabulbar block is sometimes very efficient and sometimes not, thus requiring a second or third injection. Now investigators are able to visualize where the local anaesthetics spreads with the help of ultrasound imaging. The aim of the study is to observe and to describe the incidence of intraconal spread of local anaesthetics when a peribulbar block is performed.