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M01.02.048 Eyelids
The eyelids are thin, mobile folds that serve essential functions, such as protecting the eyeball from excessive light and injury and maintaining lubrication by spreading tears across the eye’s surface.
Anatomy of the Eyelids
Structure of Eyelids
- Divisions: Upper and lower portions, meeting at the medial and lateral canthi.
- Palpebral Aperture: The opening between the two eyelids.
Layers of the Eyelids
The eyelid consists of five primary layers, arranged from superficial to deep:
| Layer | Description |
|---|---|
| Skin and Subcutaneous Tissue | Thin skin with no subcutaneous fat, allowing for easy distension (oedema/blood). Contains ciliary glands of Moll and glands of Zeis. |
| Orbicularis Oculi | Muscle responsible for eyelid movements. Contains palpebral, lacrimal, and orbital parts. |
| Tarsal Plates | Dense connective tissue providing eyelid structure. Houses Meibomian glands for tear film maintenance. |
| Levator Apparatus | Includes levator palpebrae superioris and superior tarsal muscles, aiding in eyelid elevation. |
| Conjunctiva | Thin mucous membrane lining the inner surface of the eyelid and reflecting onto the sclera. |
Detailed Layers
Skin and Subcutaneous Tissue
- Characteristics:
- Thinnest skin in the body.
- No fat; prone to distension.
- Specialized Structures:
- Ciliary Glands of Moll: Modified sweat glands near eyelashes.
- Glands of Zeis: Sebaceous glands associated with eyelashes.
Orbicularis Oculi Muscle
- Parts:
- Palpebral: Gently closes the eyelid.
- Lacrimal: Aids tear drainage.
- Orbital: Tightly closes the eyelid.
- Innervation: Facial nerve (CN VII).
Tarsal Plates
- Dense connective tissue forms scaffolding for eyelids.
- Houses Meibomian glands, which secrete an oily substance to prevent tear evaporation and eyelid adhesion.
Clinical Relevance: Tarsal Plate Disorders
| Condition | Description |
|---|---|
| Stye | Painful infection of hair follicles or Meibomian glands. Classified as internal or external. |
| Chalazion | Painless granuloma of Meibomian glands, differentiated from styes by the absence of pain. |
Levator Apparatus
| Structure | Attachments | Action | Innervation |
|---|---|---|---|
| Levator Palpebrae Superioris | Originates from lesser wing of sphenoid; inserts into upper eyelid and superior tarsal plate. | Opens eyelid | Oculomotor nerve (CN III). |
| Superior Tarsal Muscle | Originates from underside of levator palpebrae superioris; inserts into superior tarsal plate. | Assists eyelid opening | Sympathetic fibres from superior cervical ganglion. |
Conjunctiva
- Deepest layer of the eyelid.
- Palpebral Conjunctiva: Covers inner eyelid surface.
- Bulbar Conjunctiva: Reflects onto the sclera.
Vasculature
| Vascular Supply | Details |
|---|---|
| Arterial Supply | Branches from the ophthalmic artery (lacrimal, medial palpebral, supraorbital, etc.) and facial artery. |
| Venous Drainage | Medial drainage via medial palpebral vein; lateral drainage via lateral palpebral vein. |
Innervation
| Function | Innervation |
|---|---|
| Sensory | Ophthalmic nerve (V1) for upper eyelid; Maxillary nerve (V2) for lower eyelid. |
| Motor | Facial nerve (orbicularis oculi), oculomotor nerve (levator palpebrae superioris), sympathetic fibres (superior tarsal muscle). |
Points to Remember
- Eyelids are essential for protection, tear distribution, and light regulation.
- The five layers of the eyelid include skin, muscle, connective tissue, and mucosa.
- Clinical conditions like styes and chalazion differ based on pain and origin.
- Vasculature and innervation are complex, involving multiple cranial nerves and arterial branches.
Bibliography
- TeachMeSeries Ltd (2024). Anatomy of the Eyelids.