Anatomy, Head and Neck, Eye Conjunctiva

Excerpt

The conjunctiva of the eye provides protection and lubrication of the eye by the production of mucus and tears. It prevents microbial entrance into the eye and plays a role in immune surveillance. It lines the inside of the eyelids and provides a covering to the sclera. It is highly vascularized and home to extensive lymphatic vessels.

The conjunctiva can be divided into three regions: the palpebral or tarsal conjunctiva, the bulbar or ocular conjunctiva, and the conjunctival fornices. The palpebral conjunctiva is further divided into the marginal, tarsal, and orbital regions. The bulbar conjunctiva is divided into scleral and limbal parts. Finally, the conjunctival fornices are divided into the superior, inferior, lateral, and medial regions. The palpebral conjunctiva lines the eyelids. The bulbar conjunctiva is found on the eyeball over the anterior sclera. Tenon's capsule binds it to the underlying sclera. The potential space between Tenon’s capsule and the sclera is frequently used for local anesthesia. The conjunctiva has an average thickness of 33 microns. Lastly, the conjunctival fornices form the junction between the palpebral and bulbar conjunctivas. This protective covering is loose and flexible, unlike its bulbar counterpart, allowing for movement of the globe and eyelids.

The conjunctiva of the eye consists of an epithelial layer composed of stratified squamous and stratified columnar epithelium. It is non-keratinized with interspersed goblet cells. There are also present within this epithelial layer blood vessels, fibrous tissue, lymphatic channels, melanocytes, T- and B-cell lymphocytes, Langerhans cells, and accessory lacrimal glands. A deeper layer, the substantia propria or conjunctival submucosa, consists of superficial lymphoid and fibrous tissue. The substantia propria is a tissue layer that only exists in the conjunctiva, but not in other eye tissues. Numerous lymphocytes, mast cells, plasma cells, and neutrophils are present within this connective tissue layer. Finally, the deepest fibrous layer contains the nerves and vessels providing innervation and blood supply to the conjunctiva. Also located within this deep layer are the glands of Krause.

The conjunctival epithelium has a thickness of 3 to 5 cell layers thick. The basal cells of the epithelium are cuboidal and become more flattened as they approach the surface.

In the area closest to the fornix, the conjunctiva has the greatest number of goblet cells. These unicellular mucous glands are especially common in the inferior and medial conjunctiva and near the medial canthus. Away from the fornix, the number of goblet cells decreases. Additionally, the fornix has a greater number of patches of lymphocytes, which are mostly suppressor T-cells. There are patches of immune cells such as T and B lymphocytes that form conjunctiva-associated lymphoid tissue (CALT).