Lacrimal System PDF

Lacrimal System Karen Gil MD, MHSN. Development • Nasolacrimal system – Lacrimal gland, lacrimal sac, canaliculi nasolacrimal duct, caruncle from surface ectoderm 4.5 months Tear Film • 7 to 10 μm thick • Three layers – Lipid layer – Aqueous layer – Mucous layer Tear Film • Functions: – Keep...

Lacrimal System Karen Gil MD, MHSN. Development • Nasolacrimal system – Lacrimal gland, lacrimal sac, canaliculi nasolacrimal duct, caruncle from surface ectoderm 4.5 months Tear Film • 7 to 10 μm thick • Three layers – Lipid layer – Aqueous layer – Mucous layer Tear Film • Functions: – Keep the surface moist and serves as a lubricant between the globe and eyelids – Traps debris and helps remove sloughed epithelial cells and debris – Primary source of atmospheric oxygen for the cornea – Provides a smooth refractive surface necessary for optimum optical function – Contain antibacterial substances (lysozyme, beta-lysyn, lactoferrin, IgA) – Help maintain corneal hydration – Contains growth factors and peptides that can regulate ocular surface wound and repair • Epidermal growth factor (EGF) and transforming growth factor alpha (TGFa) Tear Film • 3 layers: 1. Lipid layer – 1% of the thickness of the tear film (Meibomian and Zeiss glands) • Waxy esters • Cholesterol • Free fatty acids – Function: • retards evaporation and provides lubrication for smooth eyelid movement • Provides stability to the tear film Tear Film Tear Film 2. Aqueous layer – 60-70% total tear film (main and accessory lacrimal glands) • Water • Electrolytes (Na+,K+Mg2+, Ca2+, Cl-, HCO3, PO4) • Inorganic salts • Glucose • Urea • Enzymes • Immunoglobulins (A,G,D,E,M) • Cytokines • Proteins • Peptide growth factors • Glycoproteins • Antibacterial substances (lysozyme, lactoferrin and lipocalin, Beta-lysin, defensins) • Vitamins Tear Film 3. Mucous Layer (conjunctival goblet cells) • 30-40% total tear film – – – Composed of glycocalyx of the ocular surface epithelia and mucin produced and secreted by the conjunctival goblet cells Acts as an interface that facilitate adhesion of the aqueous layer to the ocular surface Mucin also bind and entrap bacteria and viruses blocking binding sites on microbes and prevents them penetrating to the ocular surface Tear Film Stability • The eyelids spread the mucous layer evenly over the corneal epithelium • Corneal epithelium accept this mucous and encompasses the aqueous film because of the glycocalyx secreted form the corneal epithelial cells • This sugar layer overlies the corneal epithelium and absorbs the mucous creating a hydrophilic surface to accept the tears Total Volume of Tears • Total volume of tears on the ocular surface is 7 to 10 μl • Normal tear production is about 1 μl/min • Average in an eye drop contains 50 μl • The eye can only hold 20-30 μl at once Properties of the Tears • Normally the tear film is isotonic in comparison to the cornea • Electrolytes in the aqueous layer – – Na+ and Cl- ions contribute in the osmolality of the tear film – Calcium is essential for hemidesmosome formation in the basement membrane of the corneal epithelium (in excess in contact lenses users decrease acuity) – Potassium found in high concentrations is important in maintaining the health of the corneal epithelium Tear Film and Cornea Properties of the Tears • Normal osmolarity around 315 mOsm/kg • Electrolytes are responsible for the osmolarity • Vary depending in : – – – – Blink rate Humidity Ocular pathology Contact lenses • Dry eye syndrome can cause increase tear osmolarity • TX with hypotonic eye drops (osmolarity 150 mOsm/kg) Properties of the Tear Film • Average pH is 7.45 • Tears had good buffering ability , so allow the eye tolerate ophthalmic solutions with different pH 3.5-10.5 • During sleep the tears become more acidic • Most eye drops are weak bases to allow better absorption Lacrimal Secretory System The lacrimal system has a dual function: • secretory component – contributing to the formation of tears • excretory component – provides a conduit though which tears drain from the eye into the nose Lacrimal Secretory System • Includes: – Main lacrimal gland – Accessory lacrimal glands (Krause and Wolfring) – Meibomian glands – Conjunctival goblet cells Lacrimal Gland Lacrimal gland • Located in the temporal fossa of the orbital plate of the frontal bone • Posterior to the superior orbital margin • Two portions or lobes (divided by the aponeurosis of the levator muscle): – Palpebral – Orbital Lacrimal Gland Orbital portion lacrimal gland • Larger • Almond shaped • Superior surface lies against the periorbita of the lacrimal fossa • Inferior surface lies against the aponeurosis • Medial edge lies against the levator muscle • Lateral edge lies the lateral rectus muscle Lacrimal Gland Palpebral portion of the lacrimal gland • ⅓ to ½ the size of the orbital lobe • Subdivided in 2 o3 section • Lacrimal gland can be seen when you evert the upper eyelid • Ducts from both portions of the lacrimal gland exit thought the palpebral lobe Lacrimal Gland • Lacrimal gland consist of lobules made of numerous acini • Acini – is an irregular arrangement of secretory cells around a central lumen surrounded by an incomplete layer of myopeithelial cells Lacrimal Gland • A network of ducts connects the acini and drains into one of the main excretory ducts • Approximately 12 ducts that empty in the conjunctival sac in the superior fornix Lacrimal Gland • Secretion is composed of: – Water – Electrolytes – Antibacterial agents (lysozyme, lactoferrin and immunoglobulins) • Reflex secretion – Increases the volume in response to a stimulus – Both main and accessory glands play a role Blood Supply • Lacrimal Gland • Blood supplied by the lacrimal artery (branch of the ophthalmic artery) Innervation • Lacrimal gland – Sensory innervation by the lacrimal nerve (branch of ophthalmic branch of Trigeminal nerve) – Receives vasomotor sympathetic innervation and secretomotor parasympathetic innervation Blood Supply and Innervation • Reflex tearing – – Occurs by stimulation of branches of the ophthalmic division in response to external stimuli (intense light) – Afferent pathway is by the trigeminal nerve – Parasympathetic pathway is though the facial nerve Corneal Reflex. The blink reflex circuit is shown in blue, purple, and red. Arrows indicate the direction of flow. The tear production reflex utilizes the same pathways as the blink reflex. However it activates the lacrimal gland via parasympathetic branches (green line) Tear Film Distribution • Lacrimal gland fluid is secreted into the lateral part of the upper fornix • Descends across the anterior surface of the globe • Contraction of the orbicularis forces meibum out of the pores and lid motion can spread the thin lipid layer across the surface • Each blink reforms the tear film, spreading into over the ocular surface (From Zide BM, Jelkes G. Surgical Anatomy of the Orbit. New York: Raven Press, 1985.) Tear Film Distribution • Both upper and lower eyelid margins have a tear meniscus • Upper tear meniscus continuous with the lower meniscus at the lateral canthus and medial canthus • In the medial canthus the tear meniscus lead directly to punctum and drain into them (From Zide BM, Jelkes G. Surgical Anatomy of the Orbit. New York: Raven Press, 1985.) Nasolacrimal Drainage System • 75% of the tear fluid passes through the nasolacrimal drainage system • 25% is evaporated or reabsorbed through the conjunctival tissue Nasolacrimal Drainage System • Consist in: – – – – Lacrimal punctum Canaliculi Lacrimal sac Nasolacrimal duct Nasolacrimal Drainage System Lacrimal Punctum • Located in the lacrimal papilla • At the junction of the lacrimal and ciliary portions of the eyelid margin • Both lower and upper eyelids have punctum • Normally is are turned toward the globe • Each one opens into a lacrimal canaliculus Nasolacrimal Drainage System Canaliculi • Tubes in the upper and lower eyelids • Join the punctum to the lacrimal sac • Walls of the canaliculi contain elastic tissue and surrounded by fibers of the Horner’s muscle (orbicularis muscle fibers) Nasolacrimal Drainage System Canaliculi • First portion is vertical – approximately 2mm • Second portion is horizontal – Runs along the lid margin approximately 8 mm Nasolacrimal Drainage System Canaliculi • Both upper and lower canaliculi join to form a single common canaliculus (ampulla of Maier) • Piers the periorbita covering the lacrimal sac and enters the lateral aspect of the sac • Enters in an angle that produces a physiological valve (Valve of Rosenmuller) that prevents reflux, is the first valve in the system Lacrimal Sac • Lies within the lacrimal fossa • Formed by the fontal process of the maxillary bone and the lacrimal bone • Sac is surrounded by fascia that continues with the periorbita • The two limbs of the medial palpebral ligament straddle the sac to attach to the posterior and anterior crests • Orbital septum and the check ligament of the medial rectus muscle lie behind the lacrimal sac Lacrimal Sac • Lacrimal Sac – Fundus: 3-5 mm – Body: 10 mm • Lacrimal sac empties into the nasolacrimal duct Nasolacrimal duct • Lacrimal sac enters the nasolacrimal canal in the maxillary bone • Nasolacrimal duct – Interosseous part: 12 mm – Meatal part: 5mm • Drains to the inferior meatus of the nose • Valve of Hasner- mucosal fold that prevents retrograde movement of fluid up from the nasal cavity Valves • The mucous membrane within the sac and nasolacrimal duct is arranged into membranous folds that act as valves • Folds or Valves: – Valve of Rosenmuller • where the common canaliculus enters into the sac – Valve of Krause • constrictions at the junction of the sac in the nasolacrimal duct – Valve of Hyrtl and valve of Taillefer • within the nasolacrimal duct – Valve of Hasner (plica lacrimalis) • at the end of the nasolacrimal duct under the inferior turbinate 1. valve of Rosenmüller 2. valve of Krause 3. spiral valve of Hyrtl 4. valve of Taillefer 5. valve of Hasner or plica lacrimalis Tear Drainage 1. Eyelid closure start at the temporal canthus and moves toward the medial canthus 2. Tears pool in the lacrimal lade 3. Tear menisci are pushed toward the lacrimal punctum which they drain Tear Drainage 4. Contraction of the orbicularis muscle pulls on the fascial sheath attached to the lacrimal sac, causes: – – – – 5. Lateral displacement of the lateral wall Expanding the sac Creating negative pressure within it Pulling tears in from the canaliculus Orbicularis relaxation – – – Lacrimal sac collapse Tears are driven into the nasolacrimal duct Canaliculi open and act as siphons to pull tears in through the punctum Tear Drainage 6. Tears drain into the nasolacrimal duct mainly by gravity 7. Some tear is absorbed in the lining mucosa and the remaining tears enter to the inferior meatus Aging Changes • Aging process – – – – – eyelids tissue atrophies The skin loses elasticity Wrinkles appear Distance between the center of the pupil and the lower margin increases due to sagging of the lower lid (more in males) Aging Changes • Tearing causes: – Eversion of the lower punctum due to eyelid position – stenosis of the passages in the lacrimal drainage system – Basal rate of tear secretion diminishes after age 40 – Tear reflex decreases – Goblet cells decrease – Tear is more viscous don’t flow easily Tear Break Up Time • Measure the stability of the tear film • Normal TBUT is between 15 and 45 seconds • TBUT less than 10 seconds is indicative of an unstable tear film • If consistently breaks up in the same location, probably indicates a defect in the corneal epithelium Clinical Correlation • Congenital Dacryostenosis – Approximately 50% of infants are born without complete canalization of duct – approximately 4% are symptomatic – Symptoms: • Lacrimation • Discharge – High incidence of recurrence Clinical Correlation • Congenital Nasolacrimal Duct Obstruction – By far the most common congenital lacrimal abnormality – Usually due to an imperforate valve of Hasner – Could be transient – Epiphora – Irritation of the skin – If not relief 4-8 weeks after birth is considered probing Clinical Correlation Punctual Anomalies • Atresia – results if epithelization or canalization fails to reach the puncta – Surgical exploration often reveals an intact canalicular system more proximally • Supernumerary puncta are a form of fistula Clinical Correlation • Canaliculitis – Infection of the canaliculi – Pain, swelling, erythema and discharge – Frequently related to an acute actinomyces Israelli infection – Irrigation and probing usually no effective – Topical antibiotic or oral if needed Clinical Correlation • Canaliculitis Drainage – Acute canaliculitis with a pouting puncta – A posterior cut down of the canaliculus and curettage of the granules from the system is done Clinical Correlation • Dacryoadenitis – Is an inflammatory enlargement of the lacrimal gland – acute or chronic syndromes – Usually, infectious etiology – Pain, edema, erythema Clinical Correlation • Dacryocystitis – Infection of the lacrimal sac – Usually for obstruction of the nasolacrimal duct – Acute or chronic – Pain – Edema – Erythema – Purulent discharge Clinical Correlation • Dacryocystorhinostomy (DCR) Tear Break Up Time • http://www.youtube.com/watch?v=eSe8iz5Y2 YI