- Anatomy and histology of eye lids.

- Eye lid :

• It is movable muco-cutaneous fold covering anterior surface of eye globe.
• Upper eye lid is more movable than lower eye lid as it have levator palpebrae superioris muscle and Muller's muscle .
• The upper eyelid skin crease (superior palpebral furrow) is approximately 8-11 mm superior to the eyelid margin and is formed by the attachment of the superficial insertion of  levator aponeurotic fibers  (8-9 mm in men and 9-11 mm in women).

-The palpebral fissure is that empty space between the upper and  lower eyelid margins when the eyelids are open (that is, the space between the eyelids that allows you to see  your eyeball and your eyeball to see the world).
-The palpebral fissure measure ( 10-12 mm) vertically  and (25-30mm) horizontally.
- The points at which the upper and lower eyelids fuse together at both sides of the eye are called canthi.

- The edge of either eyelid (the junction where the front and back sides join together)  is called the eyelid margin= 2 mm.

-The eyelashes are located on the most forward edge of the lid margin.

-Histologically eye lid is composed from before backward :-

1-Skin, has the thinnest skin of the whole body .
2- ubcutaneous tissue:- which contain hair follicles but no fat.3- Muscular layer. 
4- Submuscular areolar tissue consists of variable loose connective tissue, infiltration anesthesia is given here. 
5- Tarsal plate:-

• The tarsal plates are composed of dense fibrous tissue and are responsible for the structural integrity of the lids.
• Each tarsus encloses about meibomian glands that traverse the vertical height of the tarsus.
• Their ducts open at the lid margin posterior to the grey line and just anterior to the mucocutaneous junction.
• The medial and lateral ends of the tarsi are attached to the orbital rims by the medial and lateral palpebral ligaments.

6-Palpebral conjunctiva.(discussed later)

*Main muscles of the eye lids*

• levator palpebrae superioris muscle .
• Muller's muscle .
• Orbicularis oculi muscle .

*nerve supply of the lid*

1-Sensory innervation of the eyelids by divisions of the trigeminal nerve (CN V) through its terminal branches the ophthalmic (for upper eye lid) and maxillary (for upper eye lid)

2- motor innervation:-

• levator palpebrae superioris muscle by 3rd cranial nerve.
• Muller's muscle by sympathetic chain(1st and 2nd thoraxic segments)
•  orbicularis oculi muscle by facial nerve.

*Blood supply of the lid*

Mmedial palpebral artery and  lateral palpebral artery arise from the ophthalmic artery .

*Lymphatic drainage*

• The eyelids and conjunctiva have a rich lymphatic drainage.
  
• The drainage of most of the upper lid and the lateral half of the lower lid is to the preauricular lymph nodes.
• The medial portion of the upper lid and the medial half of the lower lid drain into the submandibular nodes by vessels that follow the angular and facial vessels.

Thanks a lot

Dr Ibrahim