April 14, 2003
Sub-Tenon’s anesthesia
Eyeworld April 2003 
Sub-Tenon’s anesthesia provides many of the advantages of retrobulbar anesthesia, without the risks. Unlike retrobulbar anesthesia, which must be administered before surgery, sub-Tenon’s anesthesia can be administered at any time during surgery. Additionally, it achieves akinesia. This is especially helpful when surgeons use topical anesthesia and a patient has excessive ocular movement, discomfort, or surgery becomes prolonged or complicated.The only patients who are not good candidates are those who have had extensive prior conjunctival surgery such as retinal reattachment surgery or extensive eye muscle surgery where one could encounter significant scarring of the conjunctiva or those who have retinal encircling bands.
The technique
Sub-Tenon’s anesthesia can be done using several different techniques. Rous uses a technique called simplified sub-Tenon’s/parabulbar anesthesia. He uses a needle that is 9/16 inches in length with a gentle curve. The bevel of the needle is on the inside of the curve.The anesthesia is given in the inferotemporal quadrant of the eye between the equator and the fornix. “The needle is placed tangentially, and then the curve of the needle just follows the curvature of the globe. I mix 4.5 cc of 2% Carbocaine (mepivacaine HCl, Abbott) with 0.5 cc of hyaluronidase. I usually give between 3.5 and 4 cc,” Rous said.The anesthesia is given in the preop area under direct visualization and does not require any conjunctival cut down. He uses sodium Pentothal (thiopental, Abbott) to put the patient to sleep for a few minutes. He separates the lids with a wire speculum, but finger spread can also be used. After the injection is given, a Honan’s balloon is placed over the eye.
Masket’s technique is a bit different. He makes a small buttonhole through the conjunctiva and through Tenon’s capsule. “Typically, the best place is in either the supranasal or the infranasal quadrant, working back maybe 8 to 10 mm from the limbus. That gets you into the posterior sub-Tenon’s space. One just undermines a little bit with the blunt end of the scissors. Then, using a specially designed cannula, hug the contour of the globe and pass the cannula posteriorly. Once the end of the cannula is behind the equator of the eye, it’s just a matter of instilling about 2 cc or 3 cc of local anesthetic,” he said He noted that the concentration of the anesthetic and the mixture of the anesthetic can vary from patient to patient depending on need. “If one wants to make the eye totally immobile, then you want to use a long-acting anesthetic, like half 0.75% Marcaine (bupivacaine, Abbott) and half 2% lidocaine,” he said.
Posted by mehdi khanlari at April 14, 2003 09:42 AM