Anatomy of the Eyelid

Note: The library does not contain a textbook specifically authored by "Vishal Singh." The content below follows the standard eyelid anatomy framework taught in Indian ophthalmology education (as taught by Vishal Singh and others), sourced from authoritative ophthalmology and surgical references in the medical library.

Overview - The Two Lamellae

1. SKIN

• The thinnest skin of the body - almost no reticular dermis
• Highly vascular - heals rapidly with minimal scarring
• Thickens rapidly as it approaches the orbital rim and hair-bearing periorbital areas

2. ORBICULARIS OCULI MUSCLE (Anterior lamella)

• The pretarsal and preseptal portions have two heads at their origin (related to lacrimal crest and canthal tendon)
• Laterally, all three segments fuse to form the lateral canthal tendon, which inserts into the Whitnall tubercle
• The orbicularis is also essential for the lacrimal pump mechanism - propels tears into puncta, canaliculi, and lacrimal sac. Facial nerve palsy disrupts this, leading to epiphora.

3. ORBITAL SEPTUM

• Lies just deep to the orbicularis oculi muscle
• Forms the anterior border of the orbit
• Confines the orbital fat
• It is a fibrous sheath formed at the orbital rims at the arcus marginalis (extension of orbital periosteum)
• In Caucasians: the septum fuses with the levator aponeurosis ~3 mm above the superior tarsal border
• In Asians: this fusion occurs more inferiorly (below the superior tarsal border), allowing orbital fat to prolapse anteriorly - this prevents a prominent upper lid crease and creates fullness of the upper eyelid

4. EYELID FAT PADS

5. EYELID RETRACTORS

Upper Eyelid Retractors

• Main retractor of the upper eyelid
• Inserts into the upper third of the tarsal plate via the levator aponeurosis
• Some fibers fuse with the orbital septum 2-5 mm above the superior tarsal border and insert into the skin, forming the upper eyelid crease
• Attaches medially to the medial canthal tendon and laterally to the lateral canthal tendon
• Suspended by Whitnall's ligament superiorly

• Arises from the undersurface of the levator aponeurosis just below Whitnall's ligament
• Courses inferiorly 10-12 mm to attach to the superior tarsal plate
• Nerve supply: Sympathetic (loss causes 2-3 mm ptosis in Horner's syndrome)
• Produces 2-3 mm of eyelid elevation
• Anteriorly adherent to levator aponeurosis; posteriorly loosely adherent to conjunctiva

Lower Eyelid Retractors

• Originates from the fascia of the inferior rectus muscle
• Inserts on the inferior tarsal border
• Mimics movement of the inferior rectus muscle

• Arises from the undersurface of the capsulopalpebral fascia
• Sympathetically innervated

6. TARSUS (Tarsal Plate - Posterior lamella)

• Dense fibrous connective tissue forming the skeleton of the eyelids
• Each plate is 25-30 mm in horizontal dimension
• Vertical height:
  • Upper eyelid tarsus: 10-12 mm
  • Lower eyelid tarsus: 3-5 mm
• Contains Meibomian glands (modified sebaceous glands - ~25 in upper, ~20 in lower lid) that open at the lid margin

7. CONJUNCTIVA (Posterior lamella)

• Innermost surface of the eyelid
• Nonkeratinized stratified squamous epithelium with goblet cells (produce mucous layer of tear film)
• Palpebral conjunctiva: lines the eyelid
• Bulbar conjunctiva: lines the globe
• They meet at the fornix

Surface Anatomy - Key Measurements

• Upper eyelid margin: rests midway between the superior corneal limbus and the pupil
• Lower eyelid margin: abuts the inferior corneal limbus
• The lateral canthal angle is more acute and sits 2 mm higher than the rounded medial canthal angle

Glands of the Eyelid (Summary)