Features
The space between the two eyelids is the palpebral fissure.
The two lids are fused with each other to form the medial and
lateral angles or canthi of the eye.
At the inner canthus, there is a small triangular space, the
lacus lacrimalis.
Within it, there is an elevated lacrimal caruncle, made up of
modified skin and skin glands.
Lateral to the caruncle, the bulbar conjunctiva is pinched up
to form a vertical fold called the plica semilunaris.
Each eyelid is attached to the margins of the orbital opening.
Its free edge is broad and has a rounded outer lip and a
sharp inner lip.
The outer lip presents two or more rows of eyelashes or cilia,
except in the boundary of the lacus lacrimalis.
At the point where eyelashes cease, there is a lacrimal
papilla on the summit of which there is the lacrimal punctum.
Near the inner lip of the free edge, there is a row of openings
of the tarsal glands.
Structure
Each lid is made up of the following layers from without
inwards:
1. The skin is thin, loose and easily distensible by oedema
fluid or blood.
2. The superficial fascia is without any fat. It contains the
palpebral part of the orbicularis oculi.
3. The palpebral fascia of the two lids forms the orbital
septum.Its thickenings form tarsal plates or tarsi in the lids and
the palpebral ligaments at the angles. Tarsi are thin plates of
condensed fibrous tissue located near the lid margins. They
give stiffness to the lids
The upper tarsus receives two tendinous slips from the levator
palpebrae superioris, or one from voluntary part and another
from involuntary part.
Tarsal glands or meibomian glands are embedded in the
posterior surface of the tarsi; their ducts open in a row behind
the cilia.
4. The conjunctiva lines the posterior surface of the tarsus.
Apart from the usual glands of the skin, and mucous glands in
the conjunctiva, the larger glands found in the lids are:
a. Large sebaceous glands also called as Zeis's glands at the
lid margin associated with cilia.
b. Modified sweat glands or Moll's glands at the lid margin
closely associated with Zeis's glands and cilia.
c. Sebaceous or tarsal glands, these are also known as
meibomian glands.
Clinical Anatomy
The Muller's muscle or involuntary part of levator palpebrae superioris is supplied by sympathetic fibres from the superior cervical ganglion.
Paralysis of this muscle leads to partial ptosis. This is part of the Horner's syndrome. The palpebral conjunctiva is examined for anaemia and for coniunctivitis;
the bulbar coniunctiva for jaundice. Conjunctivitis is one of the commonest diseases of the eye. It may be caused by infection or by allergy.
Blood Supply
The eyelids are supplied by:
1. The superior and inferior palpebral branches of
the
ophthalmic artery
2 The lateral palpebral branch of the lacrimal artery.
They form an arcade in each lid.
The veins drain into the ophthalmic and facial veins.
Nerve Supply
The upper eyelid is supplied by the lacrimal,
supraorbital, supratrochlear and infratrochlear
nerves
from lateral to medial side.
The lower eyelid is supplied by the infraorbital and
infratrochlear nerves.
Lymphatic Drainage
The medial halves of the lids drain into the
submandibular nodes,
and the lateral halves into the preauricular
nodes
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Clinical Anatomy:
- Foreign bodies are often lodged in a groove situated 2 mm from the edge of each
eyelid.
- Chalazion is inflammation of a tarsal gland, causing a localized swelling pointing inwards.
- Ectropion is due to eversion of the lower lacrimal punctum. It usually occurs in old
age due to laxity of skin.
- Trachoma is a contagious granular conjunctivitis caused by the trachoma virus. It is regarded as the commonest cause of blindness.
- Stye or hordeolum is a suppurative inflammation of one of the glands of Zeis. The
gland is swollen, hard and painful, and the whole of the lid is oedematous. The pus
points near the base of one of the cilia.
- Blepharitis is inflammation of the eyelids, specially of the lid margin.
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