The upper and lower eyelids are movable folds which protect the eye from foreign material. Superficial to deep, layers of the eyelids generally include skin, loose connective tissue, fibres of the orbicularis oculi, the tarsal plates (Meibomian glands within) and conjunctiva. The corners formed by the upper and lower lids are the medial and lateral canthi while the opening in between is the palpebral fissure.

The tarsal plates are laminae of condensed connective tissue in each lid. The superior tarsal plate receives the main insertion of levator palpebrae superioris. Within each tarsal plate are meibomian (tarsal) glands, modified sebaceous glands that secrete meibum that create a seal when the lids are closed, waterproof the lid margins to trap tears and provide a film of oil on the cornea to keep them moist. Their openings lie just behind the eyelashes which arise from the mucocutaneous junction.

The conjunctiva is a delicate mucous membrane that lines the anterior part of the sclera as the bulbar conjunctiva (where it is thin) and the inner surface of the eyelids as the palpebral conjunctiva (where it is thick and highly vascular). Closing the lids creates a conjunctival sac, with the lines of reflection (where the bulbar conjunctiva continues as the palpebral conjunctiva) is known as the superior and inferior conjunctival fornices. Two structures bulge into the conjunctival sac medially: the lacrimal caruncle, a small elevation, and the plica semilunaris, a crescentic fold of palpebral conjunctiva that facilitates eye movement so that the sclera is not fixed to the medial canthi.