| Tenon's capsule | |
|---|---|
 The right eye in sagittal section, showing Tenon's capsule (semidiagrammatic). | |
| Details | |
| Location | Orbit (anatomy) |
| Identifiers | |
| Latin | vagina bulbi, capsula Tenoni |
| MeSH | D058475 |
| FMA | 58734 |
| Anatomical terminology | |
Tenon's capsule (/təˈnoʊn/), also known as theTenon capsule,fascial sheath of the eyeball (Latin:vagina bulbi) or thefascia bulbi, is a thin membrane which envelops the eyeball from theoptic nerve to thecorneal limbus, separating it from the orbital fat and forming a socket in which it moves.
The inner surface of Tenon's capsule is smooth and is separated from the outer surface of thesclera by theperiscleral lymph space. This lymph space is continuous with thesubdural andsubarachnoid cavities and is traversed by delicate bands of connective tissue which extend between the capsule and the sclera.
The capsule is perforated behind by the ciliary vessels and nerves and fuses with the sheath of the optic nerve and with the sclera around the entrance of theoptic nerve. In front it adheres to theconjunctiva, and both structures are attached to the ciliary region of the eyeball.
The structure was named afterJacques-René Tenon (1724–1816),[1] a French surgeon and pathologist.
Tenon's capsule is perforated by the tendons of theocular muscles and is reflected backward on each as a tubular sheath. The sheath of theobliquus superior is carried as far as the fibrous pulley of that muscle, and that on theobliquus inferior reaches as far as the floor of theorbit, to which it gives off a slip. The sheaths on the recti muscles are gradually lost in theperimysium, but they give off important expansions. The expansion from therectus superior blends with the tendon of thelevator palpebrae, and that of therectus inferior is attached to theinferior tarsus; it is the space which lies between the sclera and the capsule. The expansions from the sheaths of therecti lateralis andmedialis are strong, especially that from the latter muscle, and are attached to thezygomatic bone andlacrimal bone respectively; as they probably check the actions of these two recti, they have been named the medial and lateralcheck ligaments.
Charles Barrett Lockwood described a thickening of the lower part of Tenon's capsule, which he named thesuspensory ligament of the eye. It is slung like a hammock below the eyeball, being expanded in the center, and narrow at its extremities which are attached to thezygomatic andlacrimal bones respectively.
Tenon's capsule may be affected by a disease called idiopathic orbital inflammation, a condition of unknown etiology that is characterized by inflammation of one or more layers of the eye. The disease is also known as orbital inflammatory pseudotumor, and sometimes may only affect thelacrimal gland or theextraocular muscles.[2]
Local anaesthetic may be instilled into the space between Tenon's capsule and the sclera to provide anaesthesia for eye surgery, principally cataract surgery. After applying local anaesthetic drops to anaesthetise theconjunctiva, a small fold of conjunctiva is lifted off the eyeball and an incision made. A blunt, curved cannula is passed through the incision into theperiscleral lymph space and a volume oflocal anaesthetic solution is instilled. The advantages are a reduced risk of bleeding and of penetration of the globe, compared toperibulbar andretrobulbar approaches. Akinesia (paralysis of the external eye muscles) may be less complete, however.