The conjunctiva is a mucous membrane that lines the posterior surface of the eyelids and the anterior surface of the globe up to the limbus. It can be divided into 3 regions: palpebral, forniceal, and bulbar. The conjunctiva consists of nonkeratinized stratified squamous epithelium with goblet cells and a delicate basement membrane that rests on the underlying stroma (substantia propria) (Fig 5-1A–D). Elements of the stroma include loosely arranged collagen fibers; blood vessels and lymphatic channels; nerves; occasional accessory lacrimal glands; and resident lymphocytes, plasma cells, histiocytes, and mast cells. In places, the lymphocytes are organized into lymphoid follicles, referred to as conjunctiva-associated lymphoid tissue (CALT), which is a subtype of mucosa-associated lymphoid tissue (MALT).
Two specialized areas of the conjunctiva are the caruncle and the plica semilunaris. The caruncle, the most medial area of the bulbar conjunctiva, histologically is a transitional zone between skin and conjunctiva. Its surface consists of nonkeratinized squamous epithelium and, like skin, the caruncle contains adnexal structures such as hair follicles, sebaceous glands, and sweat glands (Fig 5-1E). The plica semilunaris, a fold of bulbar conjunctiva just temporal to the caruncle, is a vestige of the nictitating membrane found in many other species. The epithelium is rich in goblet cells, and smooth muscle fibers are often present in the stroma.
A, Bulbar conjunctiva with nonkeratinized stratified squamous epithelium. B, Palpebral conjunctiva with epithelial ridges. The stroma contains lymphatic and blood vessels (arrow) and inflammatory cells. C, Conjunctiva in the fornices contains pseudoglands of Henle (infoldings of conjunctival epithelium with abundant goblet cells [arrows]). D, Periodic acid–Schiff (PAS) stain highlights the mucin in goblet cells (arrow).E, Caruncular conjunctiva, containing sebaceous glands (S) and hair follicles (H).
(Parts A–D courtesy of Patricia Chévez-Barrios, MD; part E courtesy of George J. Harocopos, MD.)
Tenon capsule (fascia bulbi) is a fascial sheath composed of collagen that surrounds the globe and the anterior portions of the extraocular muscles, separating them from the orbital fat. The capsule lies between the conjunctiva and the sclera and is separated from the outer surface of the sclera by a potential space, the episcleral (Tenon) space. Anteriorly, Tenon capsule is connected to the sclera by fine bands of connective tissue posterior to the sclerocorneal junction. Posterior to the globe, the capsule fuses with the optic nerve sheath. See BCSC Section 2, Fundamentals and Principles of Ophthalmology, and Section 8, External Disease and Cornea, for further discussion of these structures.
Excerpted from BCSC 2020-2021 series: Section 4 - Ophthalmic Pathology and Intraocular Tumors. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.