Eyelids

Structure

• Superficial to deep: 
• Skin (thinnest in the body)
• Subcutaneous tissue
• Orbicularis oculi fibres
• Orbital septum/tarsal plates
• Levator (in upper lid)
• Conjunctiva

• Defines the anterior lamellae (skin/lashes, subcut tissue, orbicularis) from posterior lamellae (tarsal plate and conj)

• Posterior to tarsal glands the conjunctiva meets the keratinised epithelium of the skin.

• 25-35 Meibomian (tarsal) holocrine glands sit within the tarsal plates 
• Secrete the lipid layer of the tear film
• Drain into a central ductule opening at the mucocutaneous border
• Secretion increases with age
• Mixture of lipids with a melting point of 35 degrees
• There are more glands in the upper than lower tarsus

• Sebaceous glands of Zeis open into the ciliary follicles (holocrine glands):

• There are also more sebaceous glands in the upper than lower lid (two glands per cilium)

• Secrete via plasma membrane rupture which destroys the cells at time of secretion

• Modified sweat glands of Moll (apocrine glands):

• There are more in the lower than the upper lids

• They secrete via pinched off membrane vesicles containing secretion

• Note: glands of Zeis and Moll are located in the anterior lamellae of the lids, associated with the lash follicles

• Caruncle medially with adjacent plica semilunaris

Arterial supply

• Superior and inferior medial palpebral arteries are branches of ophthalmic artery

• Superior and inferior lateral palpebral arteries are branches of lacrimal artery (branch of ophthalmic)

• The two branches of each palpebral artery form marginal and peripheral arterial arches which anastomose across the lids

• Further anastomoses between the circulations of the internal and external carotid occur in the lids: branches of the superficial temporal, transverse facial and infraorbital arteries

• The arches run anterior to the tarsal plate and Muller’s muscle but behind orbicularis

• The marginal arch runs 3mm from the lid margin
• The peripheral arch is often absent inferiorly

Venous drainage

• Ophthalmic and angular veins medially
• Superficial temporal vein laterally

Lymphatic drainage

• Lateral two-thirds: superficial parotid nodes and preauricular nodes
• Medial third: submandibular nodes

Nerve supply

• Upper lids’ skin supplied by branches of the ophthalmic nerve (V1) : supratrochlear, infratrochlear, supraorbital and lacrimal

• Medial lower lids’ skin supplied by infratrochlear branch of ophthalmic

• Lateral lower lids’ skin supplied by infraorbital nerve which is the terminal branch of the maxillary nerve (V2)

Orbital septum

• Thickened continuation of the periosteum (connective tissue) both above and below
• Defines the anterior limit of the orbit
• Attached to orbital margins: arcus marginalis

• Posterior to medial palpebral ligament which attaches tarsi to lacrimal crest and frontal process of maxilla

• Anterior to lateral palpebral ligament which attaches tarsi to marginal tubercle of zygoma

• Attached to levator aponeurosis just above where the levator inserts into orbicularis (ie just above the skin crease) and just above the superior border of the tarsus

• The lower lid septum actually inserts directly onto the inferior tarsal border

Tarsal plates

• Upper tarsus: 11mm
• Lower tarsus: 4mm
• 1mm thick
• About 29mm wide
• Embedded with meibomian glands
• The bulbar conjunctiva adheres to the tarsus

Levator

• Derived from the common tendinous ring at superolateral optic foramen
• Attached to inferior surface of lesser wing of sphenoid
• Passes above superior rectus

• Fibres develop a fan-shaped aponeurosis: wider than the original muscle at the level of superior transverse ligament of Whitnall

• Aponeurosis descends behind orbital septum and inserts into tarsal plate 

• The aponeurosis divides the lacrimal gland into orbital and palpebral portions
• Lateral horn inserts into marginal tubercle of zygoma
• Medial horn blends with the septum and medial palpebral ligament.
• Note: the horns act as ‘checks’ on the action of levator with the eyelid
• Function: raises lid by 15mm

• Innervation: superior branch of oculomotor nerve which penetrates through superior rectus to reach the levator and then penetrates levator at the posterior ⅓-anterior ⅔

• Smooth muscle of Muller (superior tarsal muscle) arises from inferior surface of levator and inserts into tarsal plate

Superior transverse ligament of Whitnall

• Supports upper lid and acts as a check for the levator: prevents posterior displacement and provides a fulcrum so the direction of levator can turn from horizontal to vertical

• Comprises a bundle of fascia beneath the superior orbital rim extending from the lacrimal gland to the trochlea

• Medial insertion at the trochlea
• Lateral insertion at the frontozygomatic suture
• Weakening with age can lead to ptosis

Orbicularis oculi

• Flat elliptical striated muscle
• Orbital, palpebral (or ‘pretarsal’) and lacrimal portions
• Orbital: arises from medial palpebral ligament
• Forms circumferential fibres around orbital margin
• Some fibres insert into the skin and soft tissue of eyebrow
• Under voluntary control
• Palpebral portion is ‘button-holed’ by palpebral fissure
• Also arises from medial palpebral ligament
• Fibres intertwine to form the lateral palpebral raphe
• Sits anterior to orbital septum and tarsal plate
• Provides reflex (involuntary) blinking and some voluntary function
• Lacrimal portion attached to the posterior lacrimal crest
• Passes deep to the medial palpebral ligament 
• Attaches to posterior lacrimal crest behind the lacrimal sac
• Pull the lids and papillae medially during blinking

• Medial fibres surround the canaliculi
• Nerve supply: temporal and zygomatic branches of the facial nerve

• Contains Riolan’s muscle and Horner’s muscle
• Riolan’s muscle
• Striated muscle fibres next to anterior border of the tarsal plate
• Represents the grey line
• Extends the length of the eyelid and is the most posteriorly placed orbicularis portion

• Together with pretarsal orbicularis, surrounds the canaliculus to shorten it during blinking and promote tear drainage

Preaponeurotic fat

• Situated behind the orbital septum and in front of the muscular portion of the levator
• Divided into medial and lateral pad (larger) by the trochlea

• The medial pad is more fibrous giving it a whitish colour while the lateral pad is yellowish

Eyebrows

• 5 groups of muscles move the eyebrows

• (Occipito)Frontalis elevates the eyebrows: supplied by the temporal branches of the facial nerve

• Elevates the eyebrows and moves the scalp forward
• Produces furrows in forehead
• Extends from eyebrows to nuchal lines

• The others all depress the eyebrows

• Orbicularis oculi
• Procerus
• Depressor supericilii
• Corrugator supercilii: produces vertical furrows in forehead
• Procerus and corrugator also move the eyebrows medially
• Frontalis: deficient laterally (only supports the medial 2/3rds hence lateral ptosis)

• All are supplied by the facial nerve

Eyelashes

• Twice as many and longer on the upper lid
• 150 in the upper compared to 75 in lower lid
• Glands of Zeis and Moll open into the hair follicles
• No erector pili muscles
• Replaced every 100-150 days (3-5 months)