ANATOMY OF THE EYELID
Sagittal section in the upper lid:-
It is formed of 6 layers. From anterior to posterior they are:-
1. The skin: It is thin and elastic. It contains skin appendages as hair follicles, sebaceous glands and sweat glands.
NB. Lashes are arranged regularly. Their follicles are associated with modified sweat and sebaceous glands called Moll and Zeis glands respectively. Lashes are spaced from each other by distances that encourage parasitic infestation.
2. The subcutaneous tissue: It is loose and allows accumulation of large amount of edema. It does not contain fat cells, so that no lipoma can occur in the lids.
3. The muscular layer: It is formed of 3 muscles:
i. The orbicularis oculi.
ii. The levator palpebrae superioris (only in the upper lid).
iii. Muller's muscles.
4. The submuscular layer: it contains the nerve supply and blood supply of the lid. So that infiltration anaesthesia must be given in this layer. It is represented in the lid margin by the grey line.
5. The fibrous layer: It is formed of 3 structures:
i. The tarsus: It is the tough fibrous skeleton of the lid. It contains the Meibomian glands (about 30 glands in the upper tarsus and 20 in the lower). It is larger in the upper lid (9-12 mm in height) than in the lower lid (4-5 mm.). Both tarsi are D-shaped and measure 30 mm long and 1 mm thick.
ii. The orbital septum: It is a fibrous membrane that extends from the edge of tarsus to the orbital margin.
iii. The medial palpebral ligament (MPL): It is thick and tough.
iv. The lateral palpebral raphe: It is just a raphe formed by the insertion of palpebral portion of orbicularis oculi.
NB. The fibrous layer is the anterior boundary of the orbit, i.e; structures behind the fibrous layer are intraorbital and their enlargement causes proptosis, while structures anterior to it are extraorbital and their enlargement does not cause proptosis.
6. The Palpebral conjunctiva: It is firmly adherent to the tarsus. It contains a horizontal sulcus (sulcus subtarsalis) about 2 mm above the lid margin.
The lid margin:-
Normally the each lid margin is divided by the lacrimal papilla into 2 portions; a big outer portion carrying lashes known as the ciliary portion and a small inner portion does not carry lashes known as lacrimal portion.
The margin of the ciliary portion is formed of 2 lines (the grey and white lines) in-between 2 edges (the anterior and posterior edges).
a. The anterior edge: It is rounded and contains the lashes, modified sebaceous glands (Zeis glands) and modified sweat glands (Moll glands).
NB. The lashes are thick hairs about 150 in U.L. and 75 in L.L.. They are richly supplied by nerve fibers.
b. The grey line: It corresponds to the submuscular layer, so that the lid can be divided into 2 layers by incising this line.
c. The white line: It is the free border of tarsus containing the openings of Meibomian ducts.
d. The posterior lid edge: It is sharp to distribute the tears on the surface of the cornea.
Muscles of the lid:-
1. Orbicularis oculi (O.O.):
- It originates from the medial palpebral ligament (MPL). and adjoining bone
- Supplied by the facial (seventh) nerve.
- It is formed of the following parts:
a. Orbital portion :- Its fibers run circularly forming complete ellipses to be inserted in the MPL. Its function is strong closure of lids.
b. Palpebral portion, which is in turn subdivided into:
i. Preseptal portion ---> gentle closure of lids.
ii. Pretarsal portion ---> gentle closure of lids.
iii. Marginal portion (Riolan's muscle) ---> apposition of lid margin to the globe.
NB. Fibers of the U.L and L.L. form half ellipses to be inserted in the lateral palpebral raphe.
c. Lacrimal portion (Horner's muscle):- It originates from the anterior lacrimal crest to be inserted to the fascia around the lacrimal sac. It is responsible for the lacrimal pump:-
- During contraction it creates a negative pressure inside the sac to suck tears from the conjunctival sac.
- During relaxation there will be a positive pressure inside the sac to push tears into the nose.
2. Levator Palpebrae superioris (LPS):
- Originates form the orbital apex.
- Runs forewords underneath the roof of the orbit.
- Its aponeurosis is inserted to:
i. The lower third of the anterior surface of upper tarsus (the main insertion).
ii. The skin making a crease in the upper lid.
iii. The upper fornix.
iv. The medial and lateral palpebral ligaments.
- It is supplied by the oculomotor (third) nerve.
3. Muller's Muscle (M.M.):
It is a smooth muscle supplied by the sympathetic nervous system. It originates from the inferior surface of LPS and inserted in the upper edge of tarsus. Its contraction causes mild lid elevation.
The palpebral fissure:-
It is the opening between the 2 lids through which the eye looks. It is about 30 X 9 mm..
The normal position of the lids:
The upper lid covers the upper 2 mm of the cornea.
The lower lid is just touching the limbus.
The medial and lateral canthi:
They are the angles between the two lids. The medial canthus is rounded, while the lateral canthus is sharp.
Supplies of the lid:-
a. The arterial supply:
By the marginal and peripheral arcades.
- They are derived from the medial and lateral palpebral arteries. They are derived mainly from ophthalmic and lacrimal arteries.
- Lower lid has only a marginal arcade.
- These arcades are present in the submuscular layer
b. Venous drainage:
There are dense plexuses in the upper and lower fornices that collect venous blood medially into ophthalmic and angular veins and laterally to the superficial temporal vein.
c. Lymphatic drainage of adnexa (lids, conjunctiva and lacrimal):-
a. The medial parts of lids, conjunctiva and lacrimal sac are drained by the submandibular lymph node.
b. The lateral parts of lids, conjunctiva and lacrimal gland are drained by the pre-auricular lymph node.
d. Nerve supply:
1. Sensory supply:
i. The ophthalmic division of trigeminal supplies most of the lid (and conjunctiva) through the following branches: infratrochlear, supratrochlear, supraorbital and lacrimal nerves.
ii. The maxillary division of trigeminal supplies the middle third of lower lid (and conjunctiva) through its infraorbital branch.
2. Motor supply: - III ---> LPS.
- VII ---> O.O. - Sympathetic ---> M.M.
Functions of the lid:-
1. Protection of the eye from trauma, dust and dryness by lid closure (reflex closure, normal blinking and closure during sleep).
2. Tear physiology: - Secrets the oily layer of tears.
- Regular distribution of Tears by blinking.
- Lacrimal pump.
Classification of DISEASES OF THE LIDS
Classification of lid diseases:
I. Congenital lid anomalies.
II. Tumours of the Eyelid.
III. Inflammatory as stye, chalazion, infected chalazion and blepharitis.
IV. Lid deformity as entropion, ectropion and trichiasis.
VI. Miscellaneous subjects.