anatomy and physiology of lacrimal apparatus ppt

ANATOMY & PHYSIOLOGY OF LACRIMAL SECRETION & OUTFLOW

Presented by

Dr Rohit Rao

REFERENCES Wolff's Anatomy of the Eye and Orbit. Adler's Physiology of the Eye . The Lacrimal System Diagnosis, Management,

and Surgery by Adam J. Cohen, Michael Mercandetti & Brian G. Brazzo.

The dry eye , a practical approach by Sudi Patel & Kenny J Blades.

Jack J Kanski’s clinical ophthalmology Clinical Anatomy of the Eye by Richard S. Snell

& Michael A. Lemp.

LACRIMAL APPARATUS It is concerned with the tear formation &

transport. Lacrimal passage includes :

Lacrimal gland

Conjunctival sac

Lacrimal puncta

Lacrimal canaliculi

Lacrimal sac

The following components of the lacrimal apparatus are discussed :

Embryology

Osteology

Secretory system

Excretory system

Physiology

EMBRYOLOGY Ectodermal origin

Solid epithelial buds(first 2 months)

Superolateral conjunctival fornix.

Lacrimal sac and nasolacrimal duct : ectoderm of the naso-optic furrow or nasolacrimal furrow

The ectoderm of the furrow buries and forms a solid cord .

Canalization : begins at 4 months and may continue after birth.

OSTEOLOGY The lacrimal sac fossa is a depression in the

inferomedial orbital rim,

Maxillary and lacrimal bones.

Bordered by the anterior lacrimal crest (maxillary bone) & posterior lacrimal crest (lacrimal bone).

The fossa is approximately 16-mm high, 4- to 9-mm wide, and 2-mm deep.

The medial orbital wall : Frontal process of maxilla, lacrimal , ethmoid , lesser wing of sphenoid bone.

The frontoethmoidal suture is important in lacrimal surgery

It marks the roof of the ethmoid sinus. Bony dissection superior to this suture may expose the dura of the cranial cavity.

The nasolacrimal canal originates at base of lacrimal fossa.

Formed by the maxillary bone laterally and the lacrimal and inferior turbinate bones medially.

The width of superior opening is 4–6 mm.

The duct courses posteriorly and laterally in the bone for 12 mm to drain into the inferior meatus of the nasal cavity.

SECRETORY SYSTEM

It includes lacrimal gland, accessory glands

Lacrimal gland is above & anterolateral to globe.

Secretes tears into superior fornix.

Tears moisten & lubricates the : cornea ,

conjunctiva.

It contributes 43D of 50D of refractive power of

eye .

LACRIMAL GLAND

It consists of

Large Orbital Part

Smaller Palpebral Part

Lateral expansion of levator separates the parts

THE ORBITAL PART Paired almond-shaped glands. It is present in a fossa on the anterolateral area

of orbit It has 2 surfaces, 2 borders, 2 extremities

Superior surface Frontal bone

Inferior surface Levator palpebrae superioris & lateral rectus

Anterior border Septum orbitale

Posterior border Contact with orbital fat , level with posterior

pole.

Lateral extremity Rest on lateral rectus

Medial extremity On levator

THE PALPEBRAL PART 1/3rd size of orbital part

Superior fornix , seen on lid eversion.

It is situated upon the course of ducts

Related to levator superiorly, inferiorly to superior fornix

Posteriorly it continues with orbital part.

ACCESSORY GLANDS

Are small, compound, branched, tubular glands

Located in the middle of lid (Wolfring glands) or superior & inferior fornices (Krause glands).

Ectopic portions of lacrimal gland tissue.

It is with connective tissue coat and excretory duct.

The excretory duct splits & form intralobular ducts, connected to secretory glandular epithelia.

Secretory epithelia have elongated tubules.

True acini are absent.

HISTOLOGY Tubuloacinar with short, branched tubules

Acini are pyramidal secretory cells with apex towards a central lumen .

Myoepithelial cells., contractile & aid the secretion

In acinus, secretory cells are joined by junctional complexes

Apical microvilli extend into the lumen

Nucleus and rough endoplasmic reticulum are basal in the cells.

Abundant secretory granules, at apex .

The ducts have two or three cell layers and microvilli at luminal surface.

Plasma cells of the interstitial space are an important source of immunoglobulins secrete IgA(and fewer lgG, lgM, IgE)

BLOOD SUPPLY

Artery supply : Lacrimal artery , branch of ophthalmic artery.

Venous drainages : Ophthalmic Vein.

Lymphatic drainage : Joins that of conjunctiva & drain into the preauricular lymph nodes.

NERVE SUPPLY

Sensory nerve supply : lacrimal nerve , branch of ophthalmic division of Vth nerve

Sympathetic nerve supply : carotid plexus

Secretomotor fibers : superior salivary nucleus

EXCRETORY SYSTEM THE PUNCTA A small, round or oval orifice on the elevation,

the papilla lacrimalis.

At medial end of lid margin at the junction of its ciliated and non-ciliated parts.

Upper punctum medial to lower, from the medial canthus being 6 and 6.5 mm.

The upper punctum opens inferoposteriorly, the lower superoposteriorly.

THE LACRIMAL CANALICULI First vertical and then horizontal

Vertical part is 2 mm & turns medially at right-angle to become horizontal 8 mm

At angle - dilatation or ampulla.

The canaliculi pierce the fascia (i.e. the periorbita covering the lacrimal sac) separately,

Uniting to enter lacrimal sac.

Stratified squamous epithelium supported by elastic tissue.

THE LACRIMAL SAC Lacrimal fossa, formed by lacrimal bone and

frontal process of maxilla . The sac, closed above and open below, is

continuous with the nasolacrimal duct.

The sac is enclosed by a periorbita, splits &form the lacrimal fascia .

Relations Medial : periorbita and bone, arc of ethmoid

sinuses. Lateral : skin, orbicularis oculi, and lacrimal

fascia. Anterior: medial palpebral ligament and

angular vein. Posterior : lacrimal fascia and muscle

THE NASOLACRIMAL DUCT The nasolacrimal duct, continuation of lacrimal

sac to the inferior meatus.

15 mm.

It lies in a canal formed by the maxilla, lacrimal bone and lacrimal process of inferior concha.

It descends posterolaterally, a surface indication

a line from medial canthus to first upper molar.

The valves They are folds of mucous

membrane with no valvular function.

The most constant is the 'valve' of Hasner at the lower end.

It prevents sudden blast of air (when blowing the nose) from entenng the lacrimal sac.

Structure

Double-layered Epithelium

The superficial layer composed of columnar cells, the deeper cells being flatter.

The membranous wall of the sac is of fibroelastic tissue, the elastic element being continued around the canaliculi.

Around the nasolacrimal duct is plexus of vessels, forming erectile tissue like that on the inferior concha.

Engorgement of these vessel obstruct the duct.

The course of the lacrimal sac and duct can be demonstrated by dacryocystography

Vessels

Artery supply : palpebral branches of the ophthalmic, angular and infraorbital arteries and nasal branch of the sphenopalatine.

Venous drainages : Angular and infraorbital vessels above, below into the nasal veins

Lymphatic drainage: submandibular and deep cervical nodes.

Nerves

Infratrochlear and anterior superior alveolar nerves.

PHYSIOLOGY

The tear film overlays corneal and conjunctival epithelia.

Tears produced by the ocular surface epithelia and adnexa.

Thickness of up to 40 µm,

Volume of tears covering the ocular surface range from 2.74 ± 2.0µL to 7 µL

TEAR FILM

For mucous and aqueous layers, secretion is regulated by neural reflexes.

For the lipid layer, the blink itself regulates release of pre-secreted meibomian gland .

Tear secretion is balanced by drainage and evaporation.

Drainage is regulated by neural reflexes ,causing vasodilation and vasoconstriction of blood sinus.

Evaporation depends blink rate and temperature, humidity, and wind speed.

THE ROLES OF THE PRECORNEAL TEAR FILM To protect the cornea from drying;

To maintain the refractive power of the cornea;

To defend against eye infection;

To allow gas to move between the air and the avascular cornea;

To support corneal dehydration (assisted by the tear film hyperosmolality).

Consists of four layers

Glycocalyx Mucous layer

Aqueous layer.

Lipid layers

GLYCOCALYX Structure

The glycocalyx is a network of polysaccharides that project from cellular surfaces.

Mucins are classified into secreted and membrane-spanning mucin.

Secreted mucins are either gel-forming or small soluble

Function

The membrane-spanning mucins function to hydrate the ocular surface and serve as a barrier to pathogens.

Membrane-spanning mucins appear to be altered in dry eye

MUCOUS LAYER Structure

The mucous layer backbone is the gel-forming mucin , synthesized and secreted by conjunctival goblet cells.

Function To resistance of the eye to infection by providing

protection against microorganisms. Mucins serve as wetting agents that keep the apical

epithelia hydrated.

AQUEOUS LAYER

Lacrimal gland produce aqueous layer.

Other ocular surface epithelia also contribute to the aqueous layer, eg. conjunctiva, accessory lacrimal glands

7µm thick.

Without the lubrication , the shearing forces produced on blinking will cause accumulative ocular surface damage.

Composed of water, with many solutes, including dissolved mucins, electrolyte sand proteins.

The osmotic pressure : concentrations of sodium, potassium and chloride ions.

The tear film’s osmotic pressure is important in the control of cornea–tear film water flux.

Bicarbonate and carbonate : pH buffering, maintaining the pH at 7.3–7.6 when the eyes open & 6.8 eyes closed.

Aqueous layer function Aqueous deficiency dry eye. Protection from bacterial infection Reflex secretion washes away noxious

substances. Protects against changes in pH.

LIPID LAYER

Meibomian glands, modified sebaceous glands, that line the upper and lower eyelids.

Meibomian gland lipids are stored in vesicles.

The secretory product contains a complex mixture of lipids and proteins and is termed meibum.

Meibum is released on to the ocular surface in small amounts with each blink.

0.1m in thickness

Function Hydrophobic barrier to prevent tear overflow.

The meibom forms a water-tight seal of the apposed lid margins during sleep.

Reduce tear evaporation .

Lipids enhance the stability of the tear film and provide a smooth optical.

DISTRIBUTION OF THE TEARS Conjunctival fornices, preocular tear film, and

marginal tear strips. Marginal tear strips are wedge shaped tear

menisci, borders of upper and lower lids. Apposed lacrimal puncta dip into marginal

strip of tears  Anterior limit of the marginal strip is the

mucocutaneous junction of the lid,

CONDUCTION OF THE TEARS

Tears are lost from the conjunctiva sac by absorption, evaporation, and nasolacrimal system.

This is related to the size of the palpebral aperture, the blink rate, ambient temperature and humidity.

Tears flow the upper and lower marginal strips → upper and

lower canaliculi (capillarity+suction) Eyes close

Pretarsal orbicularis oculi compresses the ampullae+ shortens and compresses canaliculi+puncta medially.

Lacrimal part of the orbicularis oculi, contracts → compresses the sac,(positive pressure) tears → nasolacrimal duct → nose.

Eyes open Muscles relax → canaliculi and sac expand(negative

pressure)+capillarity= tears into sac.

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