Lacrimal system ppt.

The anatomy and physiology of lacrimal system

Introduction
The lacrimal apparatus comprises
• Lacrimal glands, and
• Lacrimal passages, which include: puncta, canaliculi,
lacrimal sac and nasolacrimal duct.
2

Lacrimal passages
1. Lacrimal puncta
 These are two small, rounded or oval openings on
upper and lower lids, about 6 and 6.5 mm, respectively,
temporal to the inner canthus.
 Each punctum is situated upon a slight elevation called
lacrimal papilla which becomes prominent in old age.
 Normally, the puncta dip into the lacus lacrimalis
(collection of tear fluid in the inner canthus).
4

2. Lacrimal canaliculi
 Superior and inferior canaliculi join the puncta to the lacrimal
sac.
 Each canaliculus has two parts: vertical (1–2 mm) and
horizontal (6–8 mm) which lie at right angle to each other.
 The horizontal part converges towards inner canthus to open
in the sac.
 The two canaliculi may open separately or may join to form
common canaliculus which opens immediately into the outer
wall of lacrimal sac.
 A fold of mucosa at this point forms the valve of Rosenmuller
which prevents reflux of tears.
6

3.The lacrimal sac
• 10–12 mm long and lies in the lacrimal fossa between the anterior and
posterior lacrimal crests.
It is a cystic structure lined with columnar epithelium. It is situated in the
lacrimal fossa formed by the lacrimal bone and the frontal process of the
maxilla.
The lacrimal bone and the frontal process of the maxilla separate the
lacrimal sac from the middle meatus of the nasal cavity.
In a dacryocystorhinostomy (DCR) an anastomosis is created between the
sac and the nasal mucosa to bypass an obstruction in the nasolacrimal duct.
Size: When distended, lacrimal sac is about 12–15 mm in length and 5–6
mm in breadth with a volume of about 2 cc
Parts: It has got three parts: fundus (portion above the opening of
canaliculi), body (middle part) and the neck (lower small part which is narrow
and continuous with the nasolacrimal duct). 7

4. Nasolacrimal duct (NLD)
Dimensions and location. It extends from neck of the lacrimal
sac to inferior meatus of the nose. It is about 15–18 mm long and
lies in a bony canal formed by the maxilla and the inferior
turbinate.
Direction of the NLD is downwards, backwards and laterally.
Externally, its location is represented by a line joining inner
canthus to the ala of nose. The upper end of the NLD is the
narrowest part.
Numerous membranous valves are present in the NLD, the
most important is the valve of Hasner, which is present at the
lower end of the duct and prevents reflux from the nose.
8

Lacrimal Glands
• These are serous glands situated at the upper and outer
angle of the orbit, in a depression known as the fossa for
the lacrimal gland.
• Each gland is approximately the size and shape of an
almond. It is composed of secretory epithelial cells.
• Anteriorly the gland is divided into two parts—the upper
orbital part and the lower palpebral part.
• The ducts of the lacrimal gland which are about 12 in
number open in the fornix of the upper lid.
• The glands secrete tears composed of water, salt and
lysozyme, a bactericidal enzyme. 10

Accessory Lacrimal Glands
• These are very small glands of exactly the same
structure as the lacrimal glands.
1. Glands of Krause—These are microscopic glands lying
beneath the palpebral conjunctiva between fornix and the
edge of tarsus.
These are about 42 in the upper fornix and 6–8 in the lower
fornix.
2. Glands of Wolfring—These are few in number, present
near the upper border, of the superior tarsal plate and
along the lower border of inferior tarsus. 11

Structure, blood supply and nerve supply
• All lacrimal glands are serous acini, similar in structure to the salivary glands.
Microscopically these consist of glandular tissue (acini and ducts), connective
tissue and puncta.
• Blood supply. Main lacrimal gland is supplied by lacrimal artery which is a
branch of ophthalmic artery.
• Nerve supply includes:
1. Sensory supply comes from lacrimal nerve, a branch of the ophthalmic division
of the fifth nerve.
2. Sympathetic supply comes from the carotid plexus of the cervical sympathetic
chain.
3. Secretomotor fibres are derived from the superior salivary nucleus (pons) →
greater petrosal nerve → synapse at pterygopalatine ganglion → zygomatic
nerve → lacrimal nerve → lacrimal gland.
12

 Fluid covering the
cornea and called it
precorneal film.
 consist of three layers,
which from posterior to
anterior are mucus layer,
aqueous layer and lipid
or oily layer.
13

1. Mucus layer.
 It is the innermost and about 0.2 mm thick stratum of
the tear film.
 It consists of mucin secreted by conjunctival goblet cells
and glands of Manz.
 It converts the hydrophobic corneal surface into
hydrophilic one.
14

2. Aqueous layer.
 The bulk of tear film (7.0 mm) is formed by this
intermediate layer which consists of tears secreted by the
main and accessory lacrimal glands.
 The tears mainly comprise of water and small quantities
of solutes such as sodium chloride, sugar, urea and
proteins.
 Therefore, it is alkaline and salty in taste. It also contains
antibacterial substances like lysozyme, betalysin and
lactoferrin.
15

3. Lipid or oily layer.
• This is the outermost and thinnest (0.1 mm) layer of tear
film formed at air-tear interface from the secretions of
meibomian, zeis, and moll glands.
• This layer prevents the overflow of tears, retards their
evaporation and lubricates the eyelids as they slide over
the surface of the globe
16

Functions of tear film
1. Keeps moist the cornea and conjunctiva.
2. Provides oxygen to the corneal epithelium.
3. Washes away debris and noxious irritants.
4. Prevents infection due to presence of anti-bacterial
substances.
5. Facilitates movements of the lids over the globe.
19

Secretion of tears
 Tears are continuously secreted throughout the day by
accessory (basal secretion) and main (reflex secretion)
lacrimal glands.
 Reflex secretion is in response to sensations from the
cornea and conjunctiva, probably produced by
evaporation and breakup of tear film.
 Hyperlacrimation occurs due to irritative sensations
from the cornea and conjunctiva.
 Afferent pathway of this secretion is formed by fifth
nerve and efferent by parasympathetic(secretomotor)
supply of lacrimal gland. 20

Elimination of tears From the lacrimal gland
• The tears flow downwards and laterally across the ocular
surface.
• A variable amount of tears is lost by evaporation from the
ocular surface.
• The remainder of tears flow along the superior and inferior
marginal strips and collects as lacus lacrimalis in the inner
canthus from where it is drained by the lacrimal passage
into the nasal cavity
• About 70% tears is drained via inferior canaliculus and
30% via the superior canaliculus by an active lacrimal
pump mechanism constituted by the fibres of orbicularis. 21

Cont…
• With each blink, the pretarsal orbicularis oculi muscle compresses the ampullae,
shortens and compresses the horizontal canaliculi, and closes and moves the
puncta medially, resisting reflux.
• Simultaneously, contraction of the lacrimal part of the orbicularis oculi creates a
positive pressure that forces tears down the nasolacrimal duct and into the nose,
mediated by helically arranged connective tissue fibres around the lacrimal sac.
• When the eyes open, the canaliculi and sac expand, creating negative pressure
that draws tears from the canaliculi into the sac.
22

Elimination of tears by lacrimal pump mechanism 23

Lacrimal system ppt.

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Lacrimal system ppt.