The Lacrimal Apparatus

OPTOMETRY · SEMESTER 2

Ocular Anatomy and Physiology

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The Lacrimal Apparatus

CHAPTER 4. THE LACRIMAL APPARATUS AND TEARS.

BY THE END OF THIS CHAPTER YOU WILL HAVE COVERED THE

FOLLOWING ASPECTS OF THE TOPIC:

THE LACRIMAL SECRETORY APPARATUS

THE PREOCULAR TEARFILM

THE ANATOMY OF THE LACRIMAL DRAINAGE SYSTEM

THE PHYSIOLOGY OF THE LACRIMAL DRAINAGE

SOME DISORDERS OF THE LACRIMAL APPARATUS

ARWONS

The lacrimal apparatus function
n of certain ocular tissues.
Tears are thus essential in maintaining the functional integrity of the eye
1. THE LACRIMAL SECRETORY APPARATUS. The secretory system
includes the main lacrimal gland, the accessory lacrimal glands, meibomian
and Zeis glands, and the conjunctival goblet cells.
1.1. The Lacrimal gland located in the superior lateral quadrant of the orbit
the lacrimal gland fossa, secretes tears ( aqueous secretion ) through a series
of ducts into the superior fornix. If the upper lid is everted, the lacrimal gland
can be seen above the edge of the upper tarsal plate
It is divided by
muscle, into . The
superioris
superior orbital portion is larger and almond shaped. The palpebral lobe is
one-third to one-half the size of the orbital lobe and is subdivided into two
or three sections.
The lacrimal gland consists of lobules made up of numerous acini. Each
acinus is an irregular arrangement of secretory cells around a central lumen
surrounded by an incomplete layer of myoepithelial cells. A network of ducts
connects the acini and drains into one of the main excretory ducts. There are
approximately 12 of these ducts, which empty into the conjunctival sac in
the superior fornix
Histologically, the lacrimal gland is a branched tubuloacinar gland of the
serous type,resembling the parotid gland in structure.
The secretion of the oe is ral Be .Contains also}
The blood supply of the gland is by the lacrimal artery , branch of the
ophthalmic artery.
The lacrimal vein drains into the superior ophthalmic vein and the lymphatic
vessels into the preauricular nodes.
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Innervation of the lacrimal gland:
e the lacrimal nerve, part of the ophthalmic branch of the trigemen, is
the afferent pathway in the reflex tear arc.Stimulation of receptors in
the trigemen’s distribution, activates tear production from the
lacrimal gland.
e the efferent pathway is more complicated: parasympathetic fibers
are supplied via the facial nerve Sympathetic pathways are still not
completely understood.
The gland receives vasomotor sympathetic innervation and secretomotor
parasympathetic innervation. Reflex tearing occurs with stimulation of
branches of the ophthalmic nerve or in response to external stimuli, such as
intense light; the afferent pathway is through the trigeminal nerve, and the
parasympathetic pathway is through the facial nerve
1.2. The accessory lacrimal glands of Krause and Wolfring, are located in
the superior fornix and above the superior border of the tarsus, respectively
Both contribute to the aqueous secretion of the tears.
Aqueous lacrimal secretion is divided into basal and reflex secretion.
The accessory glands are thought to be the main providers of basal tear
secretion , in contrast to reflex secretion which is produced by the lacrimal
gland , although the lacrimal gland may also have a role in basal secretion.
2. THE PREOCULAR TEAR FILM.
The preocular tear film is a layer of tears which Covers the exposed
Inteilaipebal portionvof tie Globeland Goitie’. The portion overlying the
cornea is the precorneal tear film. The tear film, which covers the anterior
surface of the globe, has several functions: (1) keeps the surface moist and
serves as a lubricant between the globe and eyelids; (2) traps debris and
helps remove sloughed epithelial cells and debris; (3) is the primary source of
atmospheric oxygen for the cornea; (4) provides a smooth refractive surface
necessary for optimum optical function;68 (5) contains antibacterial
substances (lysozyme, beta-lysin, lactoferrin, IgA) to help protect against
infection;69 and (6) helps to maintain corneal hydration by changes in
tonicity that occur with evaporation .Recent measurements of the
— tear film indicate a thickness of i to |
The precorneal tear film consists of three layers ,each of which has separate
functions.
2.1. The outer lipid layer.
This is secreted by the meibomian glands and has three main functions:
to retard the evaporation of the aqueous layer ;
e toincrease surface tension so that tears do not overflow the
lower lid margin;
e to lubricate the eyelids as they pass over the surface of the
globe.
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2.2. The middle aqueous layer.
This is secreted by the main lacrimal gland and the accessory lacrimal glands,
and has four main functions:
e it supplies oxygen to the corneal epithelium;
e it has antibacterial substances, such as lysozyme and lactoferrin;
e it provides a smooth optical surface;
e it washes away debris.
2.3. The inner mucin layer.
Secreted by the , its main function is to convert the
corneal epithelium from a
3. THE ANATOMY OF THE LACRIMAL DRAINAGE SYSTEM.
Some tear fluid is lost by evaporation and some by reabsorption through
conjunctival tissue, but approximately 75% is passed through the
nasolacrimal ioe oad ai The lacrimal Tools ald consists of the
3.1. The puncti are small openings located near the medial end of each
eyelid. They are visible to the naked eye. A small aperture, the lacrimal
punctum, is located in a
slight tissue elevation, the lacrimal papilla, at the junction of the lacrimal and
ciliary portions of the eyelid margin. Both upper and lower lids have a
punctum. The puncta are turned toward the globe and normally can be seen
only if the eyelid edge is everted slightly. Each punctum opens into a tube,
the lacrimal canaliculus
3.2. The ampulae are about 2mm long, vertically orientated.
3.3. The canaliculi are about 8mm long. In 90% of cases, the upper and
lower canaliculi form a common canaliculus which opens into the lateral wall
of the lacrimal sac. The canaliculi are tubes in the upper and lower lids that
join the puncta to the lacrimal sac. The first portion of the canaliculus is
vertical and extends approximately 2 mm; a slight dilation, the ampulla, is at
the base of this
portion of the canaliculus, The canaliculus then turns horizontally to run
along the lid margin for approximately 8 mm. The angle at which the
canaliculus enters the sac produces a physiologic valve that prevents reflux.
A small flap of mucosa
oe canaliculus and
3.4. The lacrimal sac is about 10mm long and lies in the [Berimaltossa
8.5. The nasolacrimal duct is about 12mm long and is the continuation of
the
lacrimal sac.It passes downwards, medially and posteriorly , to open into the
inferior
meatus, lateral to and below the inferior turbinate .
EE
which prevents air and debris passing up the duct during nose “ blowing’.
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Lacrimal gland Upper punctum
Upper canaliculus
Lacrimal sac
Lower punctum
Lower canaliculus
Nasolacrimal duct
Fig. 4.1. Anatomy of lacrimal drainage system.
6. THE PHYSIOLOGY OF THE LACRIMAL_ DRAINAGE.
During closure the eyelids meet first at the temporal canthus; closure then
moves toward the medial canthus, where the tears pool in the lacrimal lake.
The tear menisci are pushed toward the lacrimal puncta into which they drain.
Tears flow along the upper and lower lid margins and enter the upper and
lower canaliculi by . Capillary
attraction plays a role in moving tears into the puncta and down into the
canaliculi between blinks.
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When the eyes are opened and the muscles relaxe , the sac collapses and a
pein meee is created which forces the tears down the nasolacrimal
The valve of Rosemuller prevents reflux into the canaliculi.
The basal rate of tear secretion diminishes after age 40, contributing to dry
eye, the incidence of which increases with age.
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7. SOME DISORDERS OF THE LACRIMAL APPARATUS.
Epiphora means overflow tearing.
Nasolacrimal obstruction is an obstruction of the
.Can be
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Dacryocystitis is the inflammation of the lacrimal sac. Usually it is caused by
secondary infection accompanying a chronic nasolacrimal obstruction.
Daryoadenitis is the inflammation of the lacrimal gland.