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anatomy and physiology of lacrimal apparatus ppt

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anatomy and physiology of lacrimal apparatus

anatomy and physiology of lacrimal apparatus

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  • Conjunctiva is formed by ectoderm

anatomy and physiology of lacrimal apparatus  ppt anatomy and physiology of lacrimal apparatus ppt Presentation Transcript

  • Presented by Dr Rohit Rao
  •  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.
  •  It is concerned with the tear formation & transport.  Lacrimal passage includes : Lacrimal gland Nasolacrimal duct Conjunctival sac Lacrimal puncta Lacrimal sac Lacrimal canaliculi
  •  The following components of apparatus are discussed :  Embryology  Osteology  Secretory system  Excretory system  Physiology the lacrimal
  •  Ectodermal origin  Solid epithelial buds(first 2  Superolateral conjunctival months) 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.
  •  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 9mm 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.
  •  It includes lacrimal  Lacrimal gland is above & anterolateral to globe.  Secretes tears into  Tears moisten & gland, accessory glands superior fornix. lubricates the : cornea , conjunctiva.  It contributes 43D eye . of 50D of refractive power of
  •  It consists of  Large Orbital Part  Smaller Palpebral Part  Lateral expansion of levator separates the parts
  •  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
  •  1/3rd size of orbital part  Superior fornix  It is , seen on lid eversion. situated upon the course of ducts  Related to levator superiorly, inferiorly to superior fornix  Posteriorly it continues with orbital part.
  •  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  True acini are absent. elongated tubules.
  •  Tubuloacinar with short, branched tubules  Acini are pyramidal secretory cells with apex towards a central lumen .  Myoepithelial cells., contractile & secretion aid the
  •  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)
  •  Artery supply : Lacrimal artery , branch of ophthalmic artery.  Venous drainages : Ophthalmic Vein.  Lymphatic drainage : Joins that of conjunctiva & drain into the preauricular lymph nodes.
  •  Sensory nerve supply : lacrimal nerve , branch of ophthalmic division of Vth nerve  Sympathetic nerve supply : carotid plexus  Secretomotor fibers nucleus : superior salivary
  •  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.
  •  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.
  •  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, 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.
  •  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
  •  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 evaporation. balanced by drainage and  Drainage is regulated by neural reflexes ,causing vasodilation and vasoconstriction of blood sinus.  Evaporation depends blink rate and temperature, humidity, and wind speed.
  •  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 tear film hyperosmolality). the
  •  Consists of four layers  Glycocalyx  Mucous layer  Aqueous layer.  Lipid layers
  • 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
  • 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. 
  •  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.
  •  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.
  •  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,
  •  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.