Fascial sheath of eyeball

The fascial sheath of eyeball (a.k.a. the Tenons capsule or the bulbar fascia), is a thin fibrous connective tissue sheath that surrounds the eyeball from the optic nerve posteriorly to near the corneoscleral junction anteriorly. It separates the eyeball from the orbital fat and forms a socket within which the globe can move smoothly.

The fascial sheath lies external to the sclera and is separated from it by a potential space called the episcleral (sub-Tenons) space, which contains a thin film of fluid that facilitates friction-free ocular movements.

Extensions of fascial sheath of eyeball

• Posteriorly, the fascial sheath is pierced by the ciliary vessels and nerves and it blends with the dural sheath of the optic nerve,

• Anteriorly it attaches near the limbus and becomes continuous with the conjunctiva.

• The tendons of the extraocular muscles pierce the fascial sheath, and tubular extensions of the fascia surround these tendons as they pass towards the sclera. These fascial prolongations help support and guide ocular movements within the orbit.

For instance, as the tendon of the superior oblique muscle passes through the trochlea and reflects posteriorly toward the eyeball, it becomes enclosed by a fascial sheath derived partly from Tenons capsule. This fascial extension extends as far as the trochlear and facilitates smooth movement of the superior oblique tendon.

Medially and laterally, the fascial sheath extends onto the tendons of the medial rectus and lateral rectus muscles to form the medial and lateral check ligaments, respectively. These are fibrous expansions that attach to the medial and lateral orbital walls. The check ligaments help limit excessive movement of the eyeball during contraction of the rectus muscles and contribute to stabilization of the globe within the orbit.

Inferiorly, the fascial sheath surrounding the inferior rectus muscle blends with a thickened fascial condensation called the suspensory ligament of the eye. This ligament extends between the medial and lateral sides of the orbit and helps support the globe within the orbit and resists downward displacement of the eye.

Functions

Functionally, Tenons capsule supports and stabilizes the eyeball within the orbit while allowing free ocular movement. It also acts as a barrier limiting the spread of infection within the orbit.