anatomy and physiology of lacrimal apparatus ppt

anatomy and physiology of lacrimal apparatus

1. Anatomy & PHYSIOLOGY OF Lacrimal SECReTION & OUTFLOW Presented by Dr Rohit Rao

2. 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 .

3. Lacrimal apparatus It is concerned with the tear formation & transport. Lacrimal passage includes :

4. The following components of the lacrimal apparatus are discussed : Embryology Osteology Secretory system Excretory system Physiology

5. embryology Ectodermal origin Solid epithelial buds(first 2 months) Superolateral conjunctival fornix.

6. 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.

7. 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.

8. 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.

9. 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.

10. 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 .

11. Lacrimal gland It consists of Large Orbital Part Smaller Palpebral Part Lateral expansion of levator separates the parts

12. 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

13. Anterior border Septum orbitale Posterior border Contact with orbital fat , level with posterior pole. Lateral extremity Rest on lateral rectus Medial extremity On levator

14. The palpebral part 1/3 rd 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.

15. 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.

16. 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.

17. Histology Tubuloacinar with short, branched tubules Acini are pyramidal secretory cells with apex towards a central lumen . Myoepithelial cells., contractile & aid the secretion

18. 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 .

19. 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)

20. 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.

21. Nerve supply Sensory nerve supply : lacrimal nerve , branch of ophthalmic division of Vth nerve Sympathetic nerve supply : carotid plexus Secretomotor fibers : superior salivary nucleus

22. 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.

23. 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.

24. 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 .

25. 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

26. 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.

27. 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.

28. 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.

29. 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

30. 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.

31. 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 ± 2.0 µ L to 7 µL Tear film

32. 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.

33. 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).

34. Consists of four layers Glycocalyx Mucous layer Aqueous layer. Lipid layers

35. 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

36. 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.

37. 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.

38. 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.

39. Aqueous layer function Aqueous deficiency dry eye. Protection from bacterial infection Reflex secretion washes away noxious substances. Protects against changes in pH.

40. 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

41. 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.

42. 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,

43. 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.

44. 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.

45. Thank you