2020–2021 BCSC Basic and Clinical Science Course™
2 Fundamentals and Principles of Ophthalmology
Part I: Anatomy
Chapter 1: Orbit and Ocular Adnexa
The Tenon capsule (fascia bulbi) is an envelope of elastic connective tissue that fuses posteriorly with the optic nerve sheath and anteriorly with a thin layer of tissue, the intermuscular septum, located 3 mm posterior to the limbus. The Tenon capsule is the cavity within which the globe moves. It is composed of compactly arranged collagen fibers and a few fibroblasts.
The Tenon capsule is thickest in the area of the equator of the globe. Connections between the Tenon capsule and the periorbital tissues help suspend the globe in the orbit. The extraocular muscles penetrate this connective tissue approximately 10 mm posterior to their insertions. The connective tissues form sleeves around the penetrating extraocular muscles, creating pulleys suspended from the periorbita. These pulleys stabilize the position of the muscles relative to the orbit during eye movements. The pulleys are connected to one another and to the Tenon fascia by connective tissue bands (Fig 1-41). Age-related connective tissue degeneration can lead to acquired strabismus. Loss of Tenon capsule with age can also lead to conjunctivochalasis (redundant folds of conjunctiva between the globe and the eyelid margin).
Demer JL. Mechanics of the orbita. Dev Ophthalmol. 2007;40:132–157.
Rutar T, Demer JL. “Heavy eye” syndrome in the absence of high myopia: a connective tissue degeneration in el derly strabismic patients. J AAPOS. 2009;13(1):36–44.
Figure 1-41 Schematic representation of the orbital connective tissues. IR = inferior rectus; LPS = levator palpebrae superioris; LR = lateral rectus; MR = medial rectus; SO = superior oblique; SR = superior rectus.
(Reproduced with permission from Demer JL, Miller JM, Pouken V, Vinters HV, Glasgow BJ. Evidence for fibromuscular pulleys of the recti extraocular muscles. Invest Ophthalmol Vis Sci. 1995;36(6):1125. © Association for Research in Vision and Ophthalmology.)
Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.