lid

One of two movable folds that cover the front of the eyeball when closed; formed of a fibrous core (tarsal plate) and the palpebral portions of the orbicularis oculi muscle covered with skin on the superficial, anterior surface and lined with conjunctiva on the deep, posterior surface; rapid contraction of the contained muscle fibers produces blinking; each has fixed (orbital) and free margins, the latter separated centrally by the palpebral fissure, united at the lateral and medial palpebral commissures, and bearing eyelashes, openings of tarsal and ciliary glands and (medially) the lacrimal puncta.

Synonym(s): palpebra [TA], blepharon, lid

One of the two movable folds covering the front of the eyeball when closed; formed of a fibrous core (tarsal plate) and the palpebral portions of the orbicularis oculi muscle covered with skin on the superficial, anterior surface and lined with conjunctiva on the deep, posterior surface; rapid contraction of the contained muscle fibers produces blinking; they each have fixed (orbital) and free margins, the latter separated centrally by the palpebral fissure, united at the lateral and medial palpebral commissures, and bearing eyelashes, the openings of tarsal and ciliary glands and (medially) the lacrimal puncta.
Synonym(s): palpebra [TA] , blepharon, lid.

A pair of movable folds of skin which act as protective coverings of the eye. The upper eyelid extends downward from the eyebrow and is the more moveable of the two. When the eye is open and looking straight ahead, it just covers the upper part of the cornea; when it is closed, it covers the whole cornea. The lower eyelid reaches just below the cornea when the eye is open and rises only slightly when it shuts. Each eyelid consists of the following layers, starting anteriorly: (1) skin, (2) a layer of subcutaneous connective tissue, (3) a layer of striated muscle fibres of the orbicularis muscle, (4) a layer of submuscular connective tissue, (5) a fibrous layer, including the tarsal plates, (6) a layer of smooth muscle, (7) the palpebral conjunctiva. Syn. blephara; lids; palpebrae. See ablephary; blepharitis; ciliosis; ectropion; entropion; epicanthus; lid eversion; eyelid lamella; lagophthalmos; palpebral ligament; myokymia; orbital septum; phthiriasis; Cogan's lid twitch sign; Collier's sign; Dalrymple's sign; inferior palpebral sulcus; superior palpebral sulcus; tarsorrhaphy; tarsus; xanthelasma.
eyelids lamella The eyelid is sometimes conceptualized as consisting of an anterior and a posterior lamella. The anterior lamella consists of the skin, the layer of subcutaneous connective tissue and the layer of striated muscle fibres of the orbicularis muscle. The posterior lamella consists of the tarsal plates, a layer of smooth muscle (Müller's palpebral muscle), and the palpebral conjunctiva.
eyelids retractor muscles The eyelid muscles that open the palpebral aperture. The upper eyelid is elevated by the levator palpebrae superioris muscle and the superior tarsal muscle (of Müller) and the lower eyelid is depressed by the inferior tarsal muscle (of Müller).