Placing anesthetic agents in the retro-bulbar space provides excellent anesthesia and akinesia during ocular surgery. We have previously shown the technique of giving a retrobulbar block but this does carry the risk of a retrobulbar hemorrhage in rare cases. Another option for placement of local anesthetics into the muscle cone is performing a Sub-Tenon’s block.
The technique is to first use topical anesthesia like tetracaine 0.5% on a sponge to numb the inferior conjunctival fornix. Then Wescott scissors and toothed forceps are used to first make a small opening in the conjunctiva and then another opening in the Tenon’s layer. The Wescott scissors are then used to bluntly dissect into the retro-bulbar space. Next 1 or 2% lidocaine without epinephrine is delivered via a blunt 19 gauge cannula into the muscle cone. Within a brief period, complete anesthesia and akinesia is achieved. Note that cranial nerve IV (the trochlear nerve) is outside of the muscle cone and is not typically blocked, therefore small movement via the superior oblique muscle may still be seen.
The small openings in the conjunctiva and Tenon’s layer do not need to be sutured. They will close and heal spontaneously over the next few days.
click below to learn how to perform a Sub-Tenon’s block for ocular surgery: