Eyelids

Palpebrae

Also known as: palpebrae, lids, tarsal glands, meibomian glands

Mobile musculofibrous folds that protect the anterior eye, spread the tear film by blinking and regulate light entry; each is stiffened by a tarsal plate containing meibomian glands.

Overview

Blink rate≈15–20/min

Blink duration≈100–150 ms

Upper tarsal plate height≈10 mm

The upper and lower eyelids meet at the medial and lateral canthi, enclosing the palpebral fissure. From superficial to deep each lid consists of: thin skin (the thinnest in the body, without subcutaneous fat); loose areolar tissue; the palpebral part of orbicularis oculi; the tarsal plate (dense connective tissue) with the vertical tarsal (meibomian) glands in its substance; and the palpebral conjunctiva. The orbital septum extends from the tarsal plates to the orbital rim and forms a barrier between lid and orbit.

The upper lid is raised by levator palpebrae superioris (skeletal muscle, oculomotor nerve), whose aponeurosis inserts into the tarsal plate and skin (forming the lid crease), and by the superior tarsal muscle (of Müller) — smooth muscle supplied by sympathetic fibres, which contributes ≈1–2 mm of elevation. The lids are closed by orbicularis oculi (facial nerve): its palpebral part closes gently (blinking), its orbital part tightly (squeezing).

The lid margin carries the eyelashes (cilia) with their sebaceous glands of Zeis and modified apocrine sweat glands of Moll; behind them open the 20–30 meibomian gland orifices, and the grey line marks the plane between the anterior (skin–muscle) and posterior (tarsus–conjunctiva) lamellae.

Location

Anterior to the eyeball, attached medially and laterally to the orbital margin by the medial and lateral palpebral ligaments.

Parts & subdivisions

Tarsal plates

Dense fibrous "skeleton" of each lid (upper ≈10 mm high, lower ≈4–5 mm), anchored by the medial and lateral palpebral ligaments.

Tarsal (meibomian) glands

Modified sebaceous glands in the tarsal plates (≈25–40 in the upper lid, ≈20–30 in the lower) secreting the lipid layer of the tear film, which slows evaporation and prevents tear overflow.

Glands of Zeis and Moll

Zeis: sebaceous glands opening into lash follicles. Moll: modified apocrine sweat glands near the lashes.

Levator palpebrae superioris

Arises from the lesser wing of the sphenoid above the optic canal; inserts into the upper tarsal plate and skin; supplied by the superior division of the oculomotor nerve.

Superior tarsal (Müller) muscle

Smooth muscle deep to the levator aponeurosis; sympathetic innervation; loss causes the mild ptosis of Horner syndrome.

Orbicularis oculi

Sphincter of the eyelids (facial nerve): palpebral part for blinking, orbital part for forced closure, lacrimal part assists tear drainage.

Anatomy

Innervation

Motor: facial nerve (orbicularis oculi), oculomotor nerve (levator palpebrae superioris), sympathetic (superior tarsal muscle). Sensory: upper lid — supraorbital, supratrochlear, infratrochlear and lacrimal branches of V1; lower lid — infraorbital nerve (V2) and infratrochlear nerve.

Arterial supply

Medial and lateral palpebral arteries forming marginal and peripheral arcades (from the ophthalmic artery), with contributions from the facial, superficial temporal and infraorbital arteries.

Lymphatic drainage

Lateral lids → preauricular (parotid) nodes; medial lids → submandibular nodes.

Clinical significance

Ptosis: oculomotor palsy vs Horner syndrome

Complete ptosis with a "down and out" eye and dilated pupil indicates an oculomotor (III) palsy (levator paralysis). Mild ptosis (1–2 mm) with miosis and anhidrosis indicates Horner syndrome (loss of sympathetic supply to the superior tarsal muscle). Other causes: myasthenia gravis (fatigable), aponeurotic (age-related) ptosis.

Stye, chalazion and blepharitis

An external hordeolum (stye) is an acute staphylococcal infection of a lash follicle/gland of Zeis or Moll; an internal hordeolum involves a meibomian gland. A chalazion is a painless, chronic lipogranuloma of a blocked meibomian gland. Blepharitis is chronic lid-margin inflammation associated with meibomian gland dysfunction and dry eye.

Facial nerve palsy

Paralysis of orbicularis oculi prevents lid closure (lagophthalmos) and causes lower-lid ectropion and epiphora; the exposed cornea is at risk of ulceration and must be protected.