A thin transparent mucous membrane lining the posterior surface of the eyelids from the eyelid margin and reflected forward onto the anterior part of the eyeball where it merges with the corneal epithelium at the limbus. It thus forms a sac, the
conjunctival sac, which is open at the palpebral fissure and closed when the eyes are shut. The depths of the unextended sac are 14-16 mm superiorly and 9-11 mm inferiorly. The conjunctiva is divided into three portions: (1) The portion that lines the posterior surface of the eyelids is called the
palpebral conjunctiva. It is itself composed of the
marginal conjunctiva, which extends from the eyelid margin to the
tarsal conjunctiva; the tarsal conjunctiva, which extends from the marginal conjunctiva to the
orbital conjunctiva; and the orbital conjunctiva, which extends from the tarsal conjunctiva to the fornix. (2) That lining the eyeball is the
bulbar conjunctiva. It is itself composed of the
limbal conjunctiva, which is fused with the episclera at the limbus and the
scleral conjunctiva, which extends from the limbal conjunctiva to the fornix. (3) The intermediate part forming the bottom of the
conjunctival sac, unattached to the eyelids or the eyeball and joining the bulbar and the palpebral portion is called the
fornix (
conjunctival fold,
cul-de-sac).
See dyskeratosis;
lid eversion;
conjunctival gland;
Krause's end bulbs;
subtarsal sulcus.