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Lids and lacrimal system


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INTRODUCTION

Eye lids are movable folds which act as shutters protecting eye from external
environment. It regulates entry of light into the eye along with pupil. Whenever
any object come towards the eye, eyelid reflexly closes and protects the eyeball.
In some diseases eye lid particularly affecting its nerve supply may not close
perfectly during sleep in which case because of exposure permanent damage occur
to cornea and conjunctiva. Eye lid helps to keep the cornea moist.

DESCRIPTION OF EYE LIDS

Anatomy of Eye Lid

There are two eye lids-upper eye lid and lower eye lid in each eye.

Layers of the Eye Lid
From anterior to posterior
1) Skin
2) Muscular Layer
3) Fibrous Layer- Tarsal plate
4) Mucous membrane Layer- Conjunctiva

Skin of the Eyelid
Skin of the lid is the thinnest in the body. It is less than lmm thicknss.
It is almost transparent. It is loosely attached to underlying structures. At the margins of the eye lid skin layer ends. There is no subcutaneous fat in eye lid. Skin of the lid contain sweat gland and sebaceous gland.


Muscular Layer

MuscIes present in eye lid include:
1) Orbicularis oculi
2) Levator palpebral superioris
3) Muller's muscle

Fibrous Layer Parts
1) Tarsus
2) Orbid septum

Tarsus
Tarsus is a thickened layer and this gives strength to the lids. It does not contain any cartilage or bone. It is a thickened fibrous tissue. The height of tarsus is about lcm in, upper lid and about 5 rnm in the lower lid. Its thickness is about l=mm.

Main function of tarsus is to give structural support to eye lid.

Orbital Septum
This is a membrane like structure which arises from the superior and inferior orbital margin. It is a flexible structure and follows the movement of the lid.

Structures piercing orbital septum includes:
Lacrimal vessels and nerves
Supra-orbital vessels and nerves
Supratrochlear nerve and artery
Infratrochlear nerve
Palpebral artery and levator palpebral superioris muscle.

Palpebral Tissue
The opened lids enclose an elliptical opening between their margins end is called palpebral fissure. The palpebral fissure meet at the medial and lateral part which are known as lateral angles or canthi

The Canthi
There are two canthi:
1) Medial canthus
2) Lateral canthus

Mucous Membrane Layer (Conjunctiva)
Conjunctiva is a mucous membrane and cover the posterior aspect of the lid.

Blood Supply of Lids derived from
1) Ophthalmic Artery
2) Lacrimal Artery

Venous Drainage
Veins of the lids drain into ophthalmic veins.

Lymphatics
Medial side of the lids goes to submandibular lymph nodes and lateral side drains into preauricular lymph nodes.

Nerve Supply
There are two types of nerve supply- motor and sensory.

Motor: Orbicularis muscle supplied by Facial Nerve.
Levator palpebral superior is by the 'oculomotor Nerves.

Sensory
Upper Lids: Supra Orbital Nerve
Infra and Supra Trochleor Nerve
Lower Lids: Infraorbital Nerve

LACRIMAL SYSTEM

Eye is constantly exposed to the external enviornment.'Because of constant
exposure to different types of environment there is danger to the external structures of the eye like cornea and conjunctiva. Even microorganisms in the
environment can cause infection frequently. So as to avoid such bad external,
effects on eye, a fluid layer cover the conjunctival and cornea which is known as tear film. The system of formation and drain of the tear film from the eye is
known as lacrimal apparatus.

Lacrimal Apparatus

Lacrimal apparatus coilsists of two parts:
1) Tear production system
2) Tear drainage system
Tear Production System
Tear film is produced by lacrimal glands. There are two types of lacrimal glands:
1) Main lacrimal glands
2) Accessory lacrimal glands

Main Lacrimal Glands
Situation: Main Laciimal gland is situated at the supratemporal aspect of the orbit.
It has 6 to 12 ducts which drains into superior fornix.
Histologically lacrimal gland is a tubuloacinar gland.

Function: Function of main lacrimal gland is to produce tear under reflex
conditions. Whenever injury occurs to the external eye or any infection occur, tear is produced by the main lacrimal gland. This type of secretion is also known as reflex secretions.

Accessory Lacrimal Glands
There are two typcs of accessory Lacrimal glancls:
1) Accessory lacrimal gland of Krause
2) Accessory lacrimal glands of Wolfring

Accessory lacrimal glands produce normal tear under basal conditions. Even if
there is no stimulus, under normal conditions certain amount of tear secretion
occurs. These tear secretions are caused by these type of glands.
Deficiency tear secretion by these glands leads to a condition known as dry eye.

lacrimal Drainage System
Lacrimal fluid is ultimately drained into the nose. The path through which
lacrimal fluid passes is known as lacrimal drainage system.
Parts of Lacrimal Drainage System
1) Punctum
2) Canaliculus
3) Common canaliculus
4) Lacrimal Sac
5) Naso-Lacrimal duct

Punctum: It is an opening at the medial part of the eye lid margin. It is situated at about 6 mm from the medial canthus. Under normal circumstances punctum is not visible. Only when eye lid is pulled outwards punctum is visible. Tear film first enters the punctum and then goes to canaliculus

Lacrimal Canaliculus: Each eye lid has one canaliculus.
There Elre two parts of Canaliculus:
1) Vertical Portion
2) Horizontal Portion
Vertical Portion: It is about 2 im long. It starts from the punctum. It bends medially at almost 90' to become continuous as horizontal canaliculus. At the angle between vertical and horizontal part there is a dilation which is known as ampulla.
Horizontal Portion: It is about 8 mm. Upper canaliculus and lower canaliculus unite to form comnion canaliculus.

Common Canaliculus: Common canaliculus is formed by the joining of upper and
lower canaliculi. It drains into the laciimal sac.

Epithelium of canoliculus: Stratified squamous epithelium.

Lacrimal Sac: Lacrimal sac is situated at the medial and inferior wall of the orbit in a shallow depression which is called lacrimal fossa. It acts as a reservoir for lacrimal fluid. Lacrimal sac drains into the naso-lacrimal duct. The sac, closed above and open below, is continuous with nasolacrimal 'duct.
Parts of the lacrimal Sac:
1) Fundus, 2)Body

Naso-Lacrimal Duct:
Naso-lacrimal duct is a downward continuation of laciimal sac.
It drains into the inferior meatus of the nose. This part of the lacrimal drainage system is more prone to damage because of its proximity to the nasal cavity.
Length: 15 mm.
Situation: Situated within a canal foinied mainly by maxilla.
Opening: It opens into the inferior meatus of nose.
Valves of Hasner: Situated at the opening of the nasolacimal duct


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