subTenons

SubTenons, or the sub-Tenon's space, refers to a potential ocular space situated between Tenon's capsule and the sclera surrounding the globe. It extends from the anterior portion near the limbus toward posterior regions behind the equator, and is bordered anteriorly by Tenon's capsule and the conjunctiva. Tenon's capsule is a fascial sheath that envelops the eyeball and the extraocular muscles. The sub-Tenon's space is formed by a potential separation between the posterior surface of Tenon's capsule and the sclera, enabling the delivery of fluids or medications with a blunt cannula.

The space is most widely used for sub-Tenon anesthesia in intraocular surgery, especially cataract procedures. Local anesthetic solution is injected into the space through a small conjunctival incision with a blunt cannula, providing analgesia and akinesia with a lower risk of globe perforation than retrobulbar techniques. It is also used for local corticosteroid injections to treat postoperative inflammation or macular edema and, less commonly, for antibiotics or other agents.

Procedural notes: Typical injection volumes range from about 3 to 5 milliliters of anesthetic solution, often a mixture of lidocaine and bupivacaine. The injection is performed with the patient seated or supine, after antisepsis, via a conjunctival puncture and cannula insertion; pressure is minimized to reduce injury risk. After administration, the depth and spread of anesthesia are assessed, and the patient is monitored for complications.

Complications and considerations include globe perforation (rare), subconjunctival hemorrhage, chemosis, ptosis, diplopia, or inadequate anesthesia. Infections, elevated intraocular pressure, or steroid-related ocular effects can occur with corticosteroid injections. Sub-Tenon technique may be unsuitable in eyes with scleral thinning, infection, or prior conjunctival scarring.

Related topics include Tenon's capsule and ocular anesthesia.