CHAPTER 5

Conjunctiva

Topography

The conjunctiva is a mucous membrane lining the posterior surface of the eyelids and the anterior surface of the globe as far as the limbus. It can be subdivided into palpebral, forniceal, bulbar, and caruncular sections. The conjunctiva consists of epithelium and underlying stroma. The epithelium is nonkeratinizing stratified squamous, with goblet cells. The conjunctival epithelium is continuous with the corneal epithelium, but the latter has no goblet cells. In the forniceal and bulbar areas, the conjunctival epithelium is flat and regular, while in the palpebral area, it exhibits ridges (Fig 5-1A, B). The goblet cells of the epithelium are most numerous in the fornices and plica semilunaris (Fig 5- 1C, D). Beneath the epithelium is the conjunctival stroma, or substantia propria, which is thickest in the fornices and thinnest covering the tarsus. Constituents of this stromal layer include loosely arranged collagen fibers; vessels; lymphatics; nerves; occasional accessory lacrimal glands; and resident lymphocytes, plasma cells, macrophages, and mast cells. In places, the lymphocytes are organized into lymphoid follicles, and this conjunctiva-associated lymphoid tissue (CALT) is an example of mucosa-associated lymphoid tissue (MALT) (see the section Lymphocytic Lesions). The bulbar portion of the substantia propria fuses with the underlying Tenon capsule. In the medial canthal area, the conjunctiva forms a vertical fold, the plica semilunaris, and medial to this is the caruncle. The stroma of the caruncle is the only part of the conjunctiva that (like skin) also contains sebaceous glands and hair follicles (Fig 5-1E). See BCSC Section 2, Fundamentals and Principles of Ophthalmology, and Section 8, External Disease and Cornea, for further discussion.

Congenital Anomalies

Choristomas

A choristoma is a benign, congenital proliferation of histologically mature tissue elements not normally present at the site of occurrence. This heterotopic congenital lesion results from normal tissue migrating to or remaining in an abnormal location during embryogenesis (hence the derivation from the Greek word for “separated mass”). Examples include

limbal dermoid

lipodermoid (or dermolipoma) ectopic lacrimal gland

episcleral osseous choristoma and osseocartilaginous choristoma complex choristoma

Figure 5-1 A, Epibulbar conjunctiva with regular, nonkeratinizing stratified squamous epithelium. B, Palpebral conjunctiva with epithelial ridges. Stroma contains vessels and inflammatory cells (arrow). C, Conjunctiva at the fornix may contain pseudoglands of Henle, infoldings of conjunctiva 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.)

Dermoids are firm, dome-shaped, white-yellow papules typically at or straddling the limbus, most commonly in the inferotemporal quadrant (Fig 5-2A, B). They may also involve the central cornea. Size varies from a few millimeters to more than 1 cm. Dermoids may occur in isolation or, particularly when bilateral, as a manifestation of a congenital complex such as Goldenhar syndrome (oculoauriculovertebral dysgenesis, characterized by epibulbar dermoid, upper eyelid coloboma, preauricular skin tags, and vertebral anomalies) or linear nevus sebaceous syndrome (an oculoneurocutaneous disorder). A dermoid often contains dermal adnexal structures. The surface epithelium may or may not be keratinized (Fig 5-2C).