Anatomy of the Eyelid (Palpebra)

The Two Lamellae

Layer-by-Layer Structure (Anterior to Posterior)

1. Skin

• The eyelid skin is the thinnest skin in the body, with almost no reticular dermis
• It is highly vascular, which allows rapid healing with minimal scarring
• It thickens rapidly as it approaches the orbital rim

2. Orbicularis Oculi Muscle

3. Orbital Septum

• A fibrous membrane deep to the orbicularis
• Forms the anterior border of the orbit and confines the orbital fat
• Arises from the orbital periosteum at the arcus marginalis at the orbital rim
• In upper eyelids (in whites): fuses with the levator aponeurosis ~3 mm above the superior tarsal border
• In Asian upper eyelids: this fusion occurs more inferiorly (below the tarsal border), allowing fat to prolapse anteriorly - this prevents a prominent upper eyelid crease

4. Eyelid Retractors

• Levator palpebrae superioris - the main elevator; a striated muscle innervated by CN III (oculomotor nerve). Its aponeurosis inserts into the anterior surface of the upper tarsal plate and into the skin to create the upper eyelid crease
• Müller's (superior tarsal) muscle - arises from the undersurface of the levator aponeurosis and inserts on the superior tarsal plate. Sympathetically innervated; contributes 2-3 mm of lid elevation. Loss (e.g., Horner's syndrome) causes mild ptosis

• Capsulopalpebral fascia - the equivalent of the levator aponeurosis in the lower lid; originates from the inferior rectus muscle fascia and inserts on the inferior tarsal border
• Inferior tarsal muscle - the sympathetically innervated equivalent of Müller's muscle in the lower lid

5. Orbital Fat Pads

• Pre-aponeurotic (preaponeurotic) fat lies between the orbital septum and the levator aponeurosis (upper lid) or capsulopalpebral fascia (lower lid)
• The upper eyelid has 2 fat compartments: nasal and central
• The lower eyelid has 3 fat compartments: nasal, central, and temporal

6. Tarsal Plates (Tarsus)

• Dense fibrous connective tissue forming the structural skeleton of the eyelids
• Horizontal dimension: 25-30 mm (both lids)
• Vertical height: 10-12 mm (upper lid) vs. 3-5 mm (lower lid)
• Contains the Meibomian (tarsal) glands - modified sebaceous glands that secrete the lipid layer of the tear film

7. Conjunctiva

• The innermost layer in contact with the globe
• Composed of nonkeratinized stratified squamous epithelium with goblet cells that secrete the mucous layer of the tear film
• Palpebral conjunctiva lines the eyelid; bulbar conjunctiva lines the globe; they meet at the conjunctival fornices

Surface Anatomy

• The lateral canthal angle is more acute and lies 2 mm higher than the medial canthal angle
• The upper lid margin normally rests midway between the superior limbus and the pupil
• The lower lid margin abuts the inferior corneal limbus

Canthal Tendons

• Medial canthal tendon: has anterior and posterior limbs anchoring the medial ends of both tarsal plates to the lacrimal crest
• Lateral canthal tendon: formed by the fusion of the three orbicularis segments; inserts into the Whitnall tubercle of the zygomatic bone, ensuring eyelid-globe apposition

Blood Supply

• Anterior lamella: supplied by branches of the facial artery (external carotid system)
• Posterior lamella: supplied by branches of the ophthalmic artery (internal carotid system) via medial and lateral palpebral arteries, forming the marginal and peripheral arcades