Anatomy and physiology of lacrimal system

Anatomy and physiology of lacrimal system

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  ANATOMY AND PHYSIOLOGY OFLACRIMAL SYSTEM Dr. Dev Raj Bharati 1st YEAR RESIDENT NEH,NAMS 8th Nov,2009
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  LACRIMAL SYSTEM  SECRETORYAPPARATUS: ∙Lacrimal gland & Ducts ∙Accessory glands of Krause and Wolfring  EXCRETORY APPARATUS: ∙Puncta ∙Lacrimal canaliculi ∙ Lacrimal sac ∙ Nasolacrimal duct
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  DEVELOPMENT: Secretory Apparatus  Lacrimalgland begins to develop between 6-7th wks. of gestation  Forms as a series of ectodermal buds that grow superolaterally from the superior fornix of the conjunctiva into the underlying mesenchyme  Buds branch & canalize to form ducts of glands  Gland becomes divided into orbital & palpebral parts with development of LPS  Lacrimal gland do not function fully until 6wks. after birth which explains why new born infants do not produce tears when crying
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  DEVELOPMENT: EXCRETORY SYSTEM By the end of 5th wk., the nasolacrimal groove forms as a furrow between the nasal & maxillary prominence  In the floor of the groove, NLD develops from the linear thickening of ectoderm  Solid cord separates from adjacent ectoderm into mesenchyme forming NLD whose superior end becomes dilated to form the lacrimal sac  Canaliculi are formed from invaginated ectoderm  canalization is usually complete around the time of birth but failure of caudal end to completely canalize results in congenital NLD obstruction
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  MAIN LACRIMAL GLAND oPosition: above and anterolateral to eyeball o Parts: ∙Lateral horn of Levator aponeurosis indents the gland into:  Large orbital or superior part  Small palpebral or inferior part
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  Lo- Orbital Part Lp-Palpebral Part LA- Levator Aponeurosis
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  THE ORBITAL PART: Location: lacrimal fossa at anterolateral area of orbital roof  Almond shaped  Superior surface :convex ,lies in the fossa of frontal bone  Inferior surface:concave, lies above aponeurosis of LPS,more laterally above the upper margin of lateral rectus muscle
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  CONT…  Anterior Border:Orbital septum  Posterior Border: Orbital fat, rounded & levels with posterior pole of eye  Medial extremity: rests on Levator  Lateral extremity: rests on Lateral rectus
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  THE PALPEBRAL PART: SIZE:about 1/3rd the size of orbital part, consists of only 1or 2 lobules LOCATION: below the aponeurosis of LPS and extend into the upper eyelid, lies mainly on the superior fornix, palpebral conjunctiva & superior palpebral muscles RELATIONS: Superior surface: related to Aponeurosis of LPS Inferior surface: lateral part of superior fornix of conjunctiva
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  LACRIMAL DUCTS: 8 –12 in no. Empty into the superior cul-de-sac approx. 5mm above the lateral tarsal border after passing posterior to the aponeurosis Ducts from orbital portion run through & join the ducts of palpebral lobe
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  ACCESSORY LACRIMAL GLANDS: Glandof Krause  POSITION: between the superior fornix and tarsus as a downward continuation of palpebral part.  NUMBER: 42 in upper and 6-8 in lower fornix Gland of Wolfring: present near upper border of superior tarsal plate & along the lower border of inferior tarsus FUNCTION:Keep Cornea moist in conditions even if main lacrimal glands become non functional
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  STRUCTURE Light Microscope:  Lobulatedtubulo-acinar gland with short branched tubules  lobules are size of pin head  Lobules are separated from one another by loose connective tissue  Acini are seen as round or tube shaped masses of columnar cells with central lumen  Smallest intralobular ducts are lined with a layer of columnar or cuboidal cells and have myoepithelial cells at the periphery  Larger intralobular ducts have a two layered epithelial lining
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  CONT.. Electron microscope:  Theepithelial secretory cells of acini are surrounded by a discontinuous layer of myoepithelial cells and rest on basal lamina  The secretory cells are truncated-conical in shape,have microvilli on their apical or luminal surface  Narrow extension of acinar lumen can be seen between secretory cells known as canaliculi
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  CONT..  The secretorycell - basally located nucleus, rough surface endoplasmic reticulum, golgi complex, mitochondria,free ribosomes, lipid droplets & vacuoles Secretory granules - In apical & middle regions of cytoplasm round or ovoid either homogenous or finely granular vary in their electron density.  Secretory cells –mostly serous type but also of mucus type  Plasma cells of interstitial space – imp. Source of immunoglobulins secreted into tears.
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  ARTERIAL SUPPLY:  Lacrimalartery ,a branch of Ophthalmic artery which enters its posterior border  The infraorbital artery ,a branch of maxillary artery  Sometimes a branch of transverse facial artery
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  VENOUS & LYMPHATICDRAINAGE  VENOUS DRAINAGE: into Superior ophthalmic vein via the lacrimal vein  LYMPHATIC DRAINAGE: joins that of conjunctiva & into preauricular nodes
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  NERVE SUPPLY  Lacrimal gland receives both autonomic &sensory nerve fibres
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  THE AUTONOMIC INNERVATION The parasympathetic secretomotor nerve supply is derived from superior salivatory nucleus of facial nerve  The pre-ganglionic fibres reach pterygopalatine ganglion through facial nerve & its greater petrosal branch & through nerve of pterygoid canal  The post-ganglionic fibres then join the maxillary nerve, then into its zygomatic branch & zygomaticotemporal nerve.They reach the lacrimal gland within lacrimal nerve
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  CONT…….  The sympatheticpostganglionic fibres arise from superior cervical sympathetic ganglion then travel in plexus of nerves around the internal carotid artery  They join deep petrosal nerve,nerve of pterygoid canal ,maxillary nerve, zygomatic nerve, zygomaticotemporal nerve and finally lacrimal nerve  The sensory fibres reach the lacrimal gland in the lacrimal nerve,a branch of ophthalmic division of trigeminal nerve
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   Ruskell describesa parasympathetic pathway through orbital branches of pterygopalatine ganglion which joins a retro- orbital plexus whose rami lacrimalis carry postganglionic fibres, both sympathetic & parasympathetic .  Postganglionic sympathetic fibres may reach the gland by several routes: along lacrimal artery, through deep petrosal nerve & through lacrimal nerve.  Has identified Sympathetic fibres in the adventitia of lacrimal artery &lacrimal nerve.
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  HIGHER NERVOUS CONTROL REFLEXCONTROL OF LACRIMAL SECRETION  Excessive production of tears in emotional conditions Parasymapthetic lacrimatory nucleus of facial nerve receive afferent fibres from hypothalamus through descending autonomic pathway in reticular formation  Excessive tear production in response to Olfactory stimuli Similar pathway connect olfactory system with lacrimatory nucleus  Reflex Lacrimation secondary to cornea or conjunctival irritation sensory nuclei of ophthalmic & maxillary division of trigeminal nerve are connected to lacrimatory nucleus by internuncial neurons
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  APPLIED ANATOMY Lacrimal gland: Lacrimal ducts originate in orbital part of gland then traverses the palpebral part of gland to open into superior fornix of conjunctival sac. So surgical removal of palpebral part destroy the drainage of whole gland  Surgical damage to palpebral part of lacrimal gland may occur during surgery as it lies within the upper lid
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  APPLIED ANATOMY  Obstructionto secretion: openings of ducts into conjunctival sac may be obstructed by scarring of conjunctiva like erythema multiforme, trachoma,chemical burns, ocular cicatricial pemphigoid (Causes of Dry eye)  Tumors of lacrimal gland: ●Benign(common)--mixed cell tumor (pleomorphic adenoma),benign lymphoid hyperplasia. ●Malignant(less common)—maligant lymphoma, adenocarcinoma
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  APPLIED ANATOMY  Dacryoadenitis:Inflammation of lacrimal gland  Dacryops : cystic swelling in upper fornix due to retention of secretion following blockade of one of the lacrimal ducts  Mikulicz Syndrome: symmetrical enlargement of lacrimal & salivary glands
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  LACRIMAL SECRETION  Thesecretion are produced by acinar cells----passes into the duct----the lining cells of duct modify its composition.  Final lacrimal secretion: Lysozyme IgA B-lysin
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  FUNCTIONS OF LACRIMALSECRETION  Keep corneal epithelium moist so that the surface epithelial cells have a medium to live  First and major refractive surface of eye  Lubricate apposed surface of lids and eyeball so that it moves freely beneath the lids  Lysozyme(antibacterial enzyme) IgA(Immunoglobin) B-lysin(bactericidal protein)  secretes substance which affects ocular surface by regulating epithelial cell turnover
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  LACRIMAL PUNCTA  Entranceto the lacrimal drainage system  0.3 mm in diameter  2 small round or oval orifice situated on the papillae lacrimalis at the medial end of lid margin at the junction of its ciliated and non ciliated part  slightly inverted & lying against the globe  The punctum is in line with openings of tarsal glands  The conjunctiva surrounding the puncta is relatively avascular & thus paler than surrounding area  The upper punctum is slightly medial to lower punctum, they are 6 and 6.5mm medial to medial canthus respectively
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  CONT….  Puncta arevisible only on everting eyelids  upper punctum opens inferoposteriorly & lower punctum opens superoposteriorly  Patency maintainance by surrounding dense tissue continued with adjacent tarsal plate  The fibres of orbicularis oculi press the puncta backward towards the lacus lacrimalis. In old age there will be muscle atropy, so there will be prominence of papilla
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  APPLIED ANATOMY  Pallorof puncta is accentuated on applying lateral tension to lower lid – aids in finding a stenosed puncta  In the elderly the puncta become more prominent due to the atrophy of orbicularis
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  LACRIMAL CANALICULI  Length:10mm  Parts: Vertical--2mm Horizontal—8mm  Diameter : 0.5 mm  vertical part turns medially at a right angle to become horizontal part  Upper canaliculi runs medially & downward,the lower runs medially and upward, upper is shorter  At the junction of vertical &horizontal portions the canaliculi slightly dilate & form ampulla
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  CONT….  The canaliculipierce the periorbita covering the lacrimal sac then they enter the posterolateral surface of sac about 2.5mm below its apex either separately or united to form a common stem  In 90% of patients,upper & lower canaliculi combine to form a single common canaliculus that enters the lateral wall of sac  A small diverticulum of the sac (the sinus of Maier) is situated at the site of entry.
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  STRUCTURE  The canalicularlining - non keratinised stratified squamous epithelium, supported by elastic tissue  Very thin wall & elastic
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  CONT…..  Also surroundedby fibres of pars lacrimalis of orbicularis muscle which invert the punctum inwards the lower lid  The medial third are covered in front by two bands which connect the medial palpebral ligaments to tarsi, while behind is the lacrimal part of orbicularis oculi (horner’s muscle)  common canaliculus bends from posterior to an anterior direction behind the medial canthal tendon at an acute angle before entering sac, thus playing a role in blocking reflux
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  APPLIED ANATOMY  Wallis so thin & elastic that it can be dilated to 3 times normal diameter which is 0.5mm  Lateral traction on the lids easily straightens them to facilitate probing  Should remember the direction & length of canaliculi while passing probe  Coloured fluid injected into a canaliculi can be seen through the transluscent tissue of lid margins
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  LACRIMAL SAC  Position:lacrimal fossa, formed by lacrimal bone & frontal process of maxilla near the anterior border of medial orbital wall Length:12mm,when distended 15 mm long & 5- 6mm wide  sac closed above & open below &continuous with nasolacrimal duct below It is enclosed by periorbita splits at posterior lacrimal crest – encloses the sac – reunites at the anterior lacrimal crest- thus forms lacrimal fascia
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  CONT..  RELATIONS: Anteriorly: Medialpalebral ligament● ● Angular vein Posteriorly: Lacrimal part of● orbicularis oculi ● Orbital septum ● Check ligament of medial rectus Medially: Upper half of sac –Anterior● ethmoidal air sinus ● Lower half of sac—Anterior part of middle meatus Laterally: Skin, Part of Orbicularis● oculi ● Lacrimal fascia ● Few fibres of inferior oblique
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  STRUCTURE OF SAC Wall consists of fibroelastic tissue & is lined by 2 layers of columnar cells, goblet cells are present.  is lined by Pseudostratified columnar epithelium & wall contains elastic & lymphoid tissue
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  APPLIED ANATOMY  Dacryocystitis:An Inflammation of the lacrimal sac  Anterior to medial palpebral ligament & lateral to facial artery, angular vein crosses7- 8mm from the medial canthus. Incision for removal of sac should not be more than 2-3mm medial to medial canthus.  upper part of sac is covered anteriorly by medial palpebral ligament & covered below only by fibres of orbicularis so distension of sac with inflammatory exudate or pus will cause swelling below the lower border of ligament, abscess or fistula will point or open in this region  sudden strain on the ligament may tear the sac
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  CONT.  A sheetof areolar tissue ascends laterally from inferior edge of medial palpaebral ligament to blend with the Lacrimal facsia covering the fundus of sac,thus even relatively slight blows to the eyes may lead to swelling of the lids on blowing the nose.
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  NASOLACRIMAL DUCT  Continuationof lacrimal sac neck to the inferior meatus in the nose  Length:15-18mm, 3mm in diameter  Direction: downward, backward & laterally at 15-25◦◦  Surface anatomy: a line from medial canthus to first upper molar tooth  Position: lies in the canal formed by maxilla,lacrimal bone & lacrimal process of inferior concha
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   The wallof NLD is attached to periosteum lining the canal. Within the wall is a venous plexus which continues above with that of lacrimal sac & below with veins of nasal mucosa  opening of inferior orifice varies  Structure: 2 layers of epithelium, superficial layer composed of columnar cells & deeper cells being flatter
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  CONTD.  It connectsthe lower end of sac with inferior meatus of nose  opening of inferior orifice varies greatly i.e. rounded or slit like
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  THE VALVES  Definition:folds of mucous membrane with no valvular function.  Types valve of Rosenmuller valve of Huschke valve of Bochdalek valve of Foltz valve of medial palpebral ligament valve of Beraud or of Krause valve of taillefer valve of Hansner
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  CONT….  The ductopens below into ant part outer wall of inferior meatus of nose,the opening is guarded by a flap of mucus membrane called the valve of Hasner  The most constant is valve of Hasner(plica lacrimalis) at the lower end,a relic of fetal septum.  Well developed plica prevent a sudden blast of air entering the lacrimal sac while blowing the nose.  A fold of mucosa at the junction between common canaliculi & lacrimal sac is Valve of Rosenmuller, which prevent reflux of tear from sac back into the canaliculi,acts as one way valve
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  ARTERIAL SUPPLY TOLACRIMAL SAC AND NLD  Medial palpebral branches of ophthalmic artery  Angular artery from facial  Infraorbital artery from maxillary  Sphenopalatine artery of maxillary
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  VENOUS , LYMPHATICDRAINAGE & NERVE SUPPLY OF SAC AND NLD Venous drainage Above: drains into angular &infraorbital vessels Below: into nasal veins Lymphatics: pass to submandibular & deep cervical nodes Nerve supply: infratrochlear branch of ophthalmic division of trigeminal nerve Anterior superior alveolar nerve,a branch of maxillary div of trigeminal nerve
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  APPLIED ANATOMY  Nasolacrimalduct: direction of NLD is downward,backward and laterally. while passing probe ,it is inserted into punctum of upper lid directed vertically and medially into lacrimal sac then downward at right angle in NLD to inferior meatus. End of the probe should be visible within the nose  The distal portion of the duct bends medially in an irregular J-shape in many neonates but it tends to straighten out with growth  NLD is easily separable from bone in upper part but below it is closely adherent forming mucoperiosteum which facilitates spread of infection
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  PHYSIOLOGY OF TEARPUMP  Physiology of tear pump: Rosengren-Doane mechanism  70% of tear enter the lower canaliculus by capillarity and 30% enter the upper and some evaporate.  In young 10% & in elderly 20% or more ,tear eliminates by evaporation  Capacity of conjunctival sac :25-30 μl. When this volume exceeds then tearing occurs
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  ROSENGREN-DOANE MECHANISM
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  CONT..  Tear isproduced by main & accessory lacrimal gland---  During the act of blinking, closure of eyelids occurs from lateral to medial  Brings fluid in the conjunctival sac medially  tear then enter the canaliculi by capillarity  blinking causes contraction of lacrimal part of orbicularis muscles which dilate the sac partly by pulling medial palpebral ligament which is attached anteriorly & partly by contracting orbicularis which is attached posteriorly  this creates negative pressure so that fluid is passed into sac from canaliculi
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  CONTD….  on openingthe eye the muscle relax and the sac collapse & a positive pressure created which forces the tear passes from sac into NLD then into nose as a result of gravity  evaporation of tear in nose occur during inspiration and expiration of air.
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  TEAR FILM  Layers: 1)Thinsuperficial oily layer or lipid layer: 0.9-0.2 μm Produced by tarsal (meibomian)gland, sebaceous gland(Zeis) & sweat gland(Moll) 2)Intermediate thick aqueous layer: 6.5-7.5 μm Secreted by Main lacrimal gland & accessory gland(Gland of Krause and Wolfring) 3)Inner thin mucin layer: 0.5 μm Secreted by conjunctival goblet cells, glands of Manz & Henle
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  FUNCTIONS  Lipid layer:reduces the evaporation of underlying aqueous layer  aqueous layer: contains lysozyme, immunoglobulin, B- lysin , is defence against invading organism  Mucin layer: allows equal distribution of tear film over the ocular surface
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  APPLIED ANATOMY  Dryeye: Either due to Decreased tear production or Increased tear evaporation  Lacrimation: Excessive lacrimation occurs reflexly as in photophobia, inflammations of conjunctiva, cornea, ciliary body  Epiphora: overflow of tears from the eye due to obstruction ,stenosis, punctal malposition or functional disorder of lacrimal passages
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  © dev Juphal, Dolpa
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  Thawang, Rolpa