The conjunctiva can be broadly divided as follows: bulbar (covers the eyeball), forniceal (covers the superior and inferior fornices), and palpebral (starts at the mucocutaneous junction of the eyelid and covers the inner eyelid). The caruncle—a fleshy, ovoid modified mass approximately 5 mm high and 3 mm wide, containing the lacus lacrimalis— is attached to the inferomedial side of the plica semilunaris and bears goblet cells and lacrimal tissue, as well as hairs, sebaceous glands, and sweat glands. The plica semilunaris is a crescent-shaped vertical fold at the medial angle of the eye. The palpebral (also called tarsal) conjunctiva is tightly adherent to the underlying tarsus. The bulbar conjunctiva is loosely attached to the Tenon capsule, and both insert into the limbus.
The cell morphology of the conjunctival epithelium varies from stratified cuboidal over the tarsus and columnar in the fornices to squamous on the globe. Goblet cells account for up to 10% of basal cells of the conjunctival epithelium and are most numerous in the palpebral conjunctiva, the inferonasal bulbar conjunctiva, and in the area of the plica semilunaris.
The substantia propria of the conjunctiva consists of loose connective tissue. Conjunctiva-associated lymphoid tissue (CALT), which consists of lymphocytes and other leukocytes, is present, especially in the fornices. Lymphocytes interact with mucosal epithelial cells through reciprocal regulatory signals mediated by growth factors, cytokines, and neuropeptides.
The palpebral conjunctiva shares its blood supply with the eyelids. The bulbar conjunctiva is supplied by the anterior ciliary arteries, which arise from muscular branches of the ophthalmic artery. These capillaries are fenestrated and leak fluid, producing chemosis (conjunctival swelling), as a response to allergies or other inflammatory events.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.