M01.02.034 The Eyelids

The eyelids are thin, mobile structures that protect the eye and maintain lubrication by spreading tears over the surface. They are divided into upper and lower portions, meeting at the medial and lateral canthi. The gap between them is called the palpebral aperture.

This guide covers the anatomy, layers, vasculature, and innervation of the eyelids to aid in understanding their structure and function.

Layers of the Eyelid

The eyelid consists of five layers (from superficial to deep):

Skin and Subcutaneous Tissue
Orbicularis Oculi
Tarsal Plates
Levator Apparatus
Conjunctiva

Layer	Key Features
Skin & Subcutaneous	Thin skin, no fat; contains sebaceous glands (Zeis) and modified sweat glands (Moll).
Orbicularis Oculi	Muscle with palpebral, lacrimal, and orbital parts; facilitates eyelid closure and tear drainage.
Tarsal Plates	Dense connective tissue, houses Meibomian glands for tear film stability.
Levator Apparatus	Includes levator palpebrae superioris and superior tarsal muscles for eyelid elevation.
Conjunctiva	Mucous membrane reflected onto the sclera; forms the deepest layer of the eyelid.

Key Components of Each Layer

1. Skin and Subcutaneous Tissue

Structure: Thin, loose connective tissue.
Clinical Note: Prone to swelling from edema or bleeding.
Special Features:
- Glands of Zeis: Sebaceous glands.
- Ciliary Glands of Moll: Modified sweat glands associated with eyelashes.

2. Orbicularis Oculi

Parts and Functions:
- Palpebral: Gently closes the eyelid.
- Lacrimal: Assists in tear drainage.
- Orbital: Tightly closes the eyelid.
Attachments: Originates from the medial orbital margin, palpebral ligament, and lacrimal bone; inserts into the skin and tarsal plates.
Innervation: Facial nerve (CN VII, temporal, and zygomatic branches).

3. Tarsal Plates

Structure: Dense connective tissue forming scaffolding for the eyelids.
Function: Houses Meibomian glands for tear film stability.
Clinical Note:
- Stye: Painful infection of glands (external or internal).
- Chalazion: Painless granuloma in Meibomian glands.

4. Levator Apparatus

Muscle	Attachment	Action	Innervation
Levator Palpebrae Superioris	Origin: Lesser wing of sphenoid; Inserts: Upper eyelid	Opens the eyelid	Oculomotor nerve (CN III)
Superior Tarsal Muscle	Origin: Underside of levator palpebrae superioris	Assists in eyelid elevation	Sympathetic fibers from the cervical ganglion

5. Conjunctiva

Palpebral Conjunctiva: Lines the inner eyelid.
Bulbar Conjunctiva: Reflected onto the sclera.

Vasculature

Arterial Supply

Ophthalmic Artery: Includes lacrimal, medial palpebral, supraorbital, dorsal nasal, and supratrochlear branches.
Facial Artery: Angular branch.
Superficial Temporal Artery: Transverse facial branch.

Venous Drainage

Medial Drainage: Medial palpebral vein → Angular and ophthalmic veins.
Lateral Drainage: Lateral palpebral vein → Superficial temporal vein.

Innervation

Sensory Innervation

Nerve	Region	Branches
Ophthalmic (V1)	Upper eyelid	Supraorbital, supratrochlear, infratrochlear, lacrimal
Maxillary (V2)	Lower eyelid	Infraorbital, zygomaticofacial

Motor Innervation

Orbicularis Oculi: Facial nerve (CN VII).
Levator Palpebrae Superioris: Oculomotor nerve (CN III).
Superior Tarsal Muscle: Sympathetic fibers.

Clinical Correlations

Styes vs. Chalazion

Condition	Cause	Painful?	Treatment
Stye	Infection of hair follicle or gland	Yes	Often self-limiting; warm compress
Chalazion	Granuloma of Meibomian gland	No	May require surgical excision

Points to Remember

The eyelids protect the eye and distribute tears.
They consist of five layers, with distinct structural and functional roles.
Key clinical conditions include styes (painful infections) and chalazia (painless swellings).
The levator apparatus and orbicularis oculi control eyelid movement.
Rich vascular and nerve supplies make eyelid anatomy crucial for systemic health understanding.

References

TeachMeSeries Ltd (2024). Eyelid Anatomy.
Gray’s Anatomy (41st Edition).

M01 Human Anatomy

Curriculum