The conjunctiva is the mucous membrane of the eye. It lines the inner surfaces of the eyelids or palpebræ, and is reflected over the forepart of the sclera and cornea.
The conjunctiva helps lubricate the eye by producing mucus and tears, although a smaller volume of tears than the lacrimal gland. It also contributes to immune surveillance and helps to prevent the entrance of microbes into the eye.
The Palpebral conjunctiva (Palpebral Portion) is thick, opaque, highly vascular, and covered with numerous papillæ, its deeper part presenting a considerable amount of lymphoid tissue. At the margins of the lids it becomes continuous with the lining membrane of the ducts of the tarsal glands, and, through the lacrimal ducts, with the lining membrane of the lacrimal sac and nasolacrimal duct. At the lateral angle of the upper eyelid the ducts of the lacrimal gland open on its free surface; and at the medial angle it forms a semilunar fold, the plica semilunaris. The line of reflection of the conjunctiva from the upper eyelid on to the bulb of the eye is named the superior fornix, and that from the lower lid the inferior fornix.
The bulbar conjunctiva (Bulbar Portion)- Upon the sclera, the conjunctiva is loosely connected to the bulb of the eye; it is thin, transparent, destitute of papillæ, and only slightly vascular. Upon the cornea, the conjunctiva consists only of epithelium, constituting the epithelium of the cornea. Lymphatics arise in the conjunctiva in a delicate zone around the cornea, and run to the ocular conjunctiva.
The histology of conjunctiva consists of non-keratinized, stratified squamous epithelium, with interspersed goblet cells. The epithelial layer contains blood vessels, fibrous tissue, and lymphatic channels. Accessory lacrimal glands in the conjunctiva constantly produce the aqueous portion of tears. Additional cells present in the conjunctival epithelium include melanocytes, T and B cell lymphocytes.