LACRIMAL APPARATUS

 LACRIMAL APPARATUS... 

INTRODUCTION:-

The structure concerned with the secretion and drainage of the lubricant and antiseptic lacrimal Or tear fluid constitute the lacrimal apparatus. 

COMPONENTS OF LACRIMAL APPARATUS:-

1. Lacrimal gland and it's duct

2. Conjunctival sac

3. Lacrimal puncta and lacrimal canaliculi

4. Lacrimal sac

5. Naso lacrimal duct

STRUCTURE OF LACRIMAL APPARATUS:-

DESCRIPTION OF THE  COMPONENT PART:-

LACRIMAL GLAND:-

The lacrimal gland is a J - shaped serous gland. 

PARTS:- 

It consists of upper large orbital part and lower small palpebral part. 

The two parts are continuous with each other around the lateral margin of the levator palpebrae superioris. 

Orbital part:-

The orbital part is almond shaped. 

It is situated in the lacrimal fossa in the anterolateral part of the roof of the bony orbit. 

Palpebral part:-

The palpebral part is one - third of the size of the orbital part. 

It is situated in the lateral part of the upper eyelid below the levator palpebrae superioris. 

It extends upto the superior fornix of conjunctiva. 

ACCESSORY LACRIMAL GLAND:-

These are very small serous glands located beneath the palpebral conjunctiva near the fornices. 

They are about 35 - 40 in the upper eyelid and 6 - 8 in the lower eyelid. 

It is also known as glands of krause. 

DUCTS OF THE LACRIMAL GLAND:-

The duct of lacrimal gland are approximately 12 in number, about 4 or 5 from orbital part and 6 - 8 from palpebrae part. 

They open into the lateral parts of the superior fornix of the conjunctival sac. 

Lacrimal gland secretes the lacrimal Or tear fluid and it's ducts convey it to conjunctival sac. 

About 1mL of lacrimal fluid is secreted per day.

Half of it evaporates and remaining half is drained into lacrimal sac. 

FUNCTIONS OF LACRIMAL FLUID:-

1. Flushes the conjunctiva and keep the cornea moist. 

2. Provides nourishment to cornea. 

3. Serves to express emotions - shedding of tears during grief and sorrow. 

4. Prevents infection ( for it contains bactericidal lysozyme). 

APPLIED ANATOMY:-

When lacrimal gland fails to secrete lacrimal fluid as in case of Bell's palsy, the artificial tears are instilled in the eye at regular intervals to prevent the cornea from dying and desiccation. 

Ducts from orbital part traverse the palpebral part to open into conjunctival sac. Therefore, removal of palpebral part of gland is functionally equivalent to removal of the entire lacrimal gland. 

After removal, the conjunctiva and cornea are moistened by accessory lacrimal gland. 

ARTERIAL SUPPLY:- 

It is supplied by lacrimal branch of ophthalmic artery. 

VENOUS SUPPLY:-

It is supplied by ophthalmic veins. 

NERVE SUPPLY OF LACRIMAL GLAND:-

The lacrimal gland is supplied by parasympathetic ( secretomotor ), sympathetic ( vasomotor), and sensory fibres through lacrimal nerves. 

PARASYMPATHETIC PATHWAY OF LACRIMAL GLAND

SYMPATHETIC PATHWAY OF LACRIMAL GLAND

SENSORY SUPPLY

It is supplied by sensory fibres of lacrimal nerve, a branch of ophthalmic division of trigeminal nerve. 

CONJUNCTIVAL SAC:-

It is a potential space between palpebral and bulbar conjunctiva. 

LACRIMAL PUNCTA:-

These are small openings on the lid margins. 

LACRIMAL CANALICULI:-

There are two lacrimal canaliculi, 

superior and inferior in upper and lower eyelids, respectively. 

Each canaliculus measures about 10 mm in 

length and begins at lacrimal punctum. 

The superior canaliculus at first runs upwards and then bends downwards 

and medially along the free margin of the eyelid to open into the lacrimal sac.

The inferior canaliculus at first runs downwards and then bends upwards and medially to open into the lacrimal sac. 

At the bending each canaliculus presents a small dilatation called ampulla. 

LACRIMAL SAC:-

It is a membranous sac, 12 mm long and 5 mm wide. 

It is situated in the lacrimal groove behind the medial palpebral ligament. 

Its upper end is blind. 

The lower end is continuous with the nasolacrimal duct.

RELATIONS:-

Anteriorly - medial palpebral ligament.

Posteriorly - Lacrimal part of orbicularis oculi. 

Medially - lacrimal groove and minute arterial plexus. 

Laterally - lacrimal fascia, which is derived from orbital periosteum and minute plexus of veins. 

NASOLACRIMAL DUCT:-

It is a membranous passage, 18 mm long.

It begins atthe lower end of the lacrimal sac, runs downwards, backwards and laterally, and opens into the inferior meatus of the nose. 

A fold of mucous membrane, called

the valve of Hasner, forms an imperfect valve at the lower end of the duct. 

Factors Helping the Drainage of Tears

Drainage of tears occurs by following means:

1. Blinking movements of eyelids.

2. Capillary action of the film of the fluid.

3. Contraction of lacrimal part of orbicularis oculi leading