DETAILED ANATOMY OF LACRIMAL APPARATUS (2).pptx

ANATOMY OF LACRIMAL APPARATUS

1. The anatomy and physiology of lacrimal system

2. Introduction 2 The lacrimal apparatus comprises Lacrimal glands, and Lacrimal passages, which include: puncta, canaliculi, lacrimal sac and nasolacrimal duct.

3. The lacrimal system 3

4. Lacrimal passages 4 1. Lacrimal puncta These are two small, rounded or oval openings on upper and lower lids, about 6 and 6.5 mm, respectively, temporal to the inner canthus. Each punctum is situated upon a slight elevation called lacrimal papilla which becomes prominent in old age. Normally, the puncta dip into the lacus lacrimalis (collection of tear fluid in the inner canthus).

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6. 2. Lacrimal canaliculi 6 Superior and inferior canaliculi join the puncta to the lacrimal sac. Each canaliculus has two parts: vertical (1–2 mm) and horizontal (6–8 mm) which lie at right angle to each other. The horizontal part converges towards inner canthus to open in the sac. The two canaliculi may open separately or may join to form common canaliculus which opens immediately into the outer wall of lacrimal sac. A fold of mucosa at this point forms the valve of Rosenmuller which prevents reflux of tears.

7. 3.The lacrimal sac 10–12 mm long and lies in the lacrimal fossa between the anterior and posterior lacrimal crests. It is a cystic structure lined with columnar epithelium. It is situated in the lacrimal fossa formed by the lacrimal bone and the frontal process of the maxilla. The lacrimal bone and the frontal process of the maxilla separate the lacrimal sac from the middle meatus of the nasal cavity. In a dacryocystorhinostomy (DCR) an anastomosis is created between the sac and the nasal mucosa to bypass an obstruction in the nasolacrimal duct. Size: When distended, lacrimal sac is about 12–15 mm in length and 5–6 mm in breadth with a volume of about 2 cc Parts: It has got three parts: fundus (portion above the opening of canaliculi), body (middle part) and the neck (lower small part which is narrow and continuous with the nasolacrimal duct). 7

8. 4. Nasolacrimal duct (NLD) 8 Dimensions and location. It extends from neck of the lacrimal sac to inferior meatus of the nose. It is about 15–18 mm long and lies in a bony canal formed by the maxilla and the inferior turbinate. Direction of the NLD is downwards , backwards and laterally. Externally, its location is represented by a line joining inner canthus to the ala of nose. The upper end of the NLD is the narrowest part. Numerous membranous valves are present in the NLD, the most important is the valve of Hasner, which is present at the lower end of the duct and prevents reflux from the nose.

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10. Lacrimal Glands 10 These are serous glands situated at the upper and outer angle of the orbit, in a depression known as the fossa for the lacrimal gland. Each gland is approximately the size and shape of an almond. It is composed of secretory epithelial cells. Anteriorly the gland is divided into two parts—the upper orbital part and the lower palpebral part. The ducts of the lacrimal gland which are about 12 in number open in the fornix of the upper lid. The glands secrete tears composed of water, salt and lysozyme, a bactericidal enzyme.

11. Accessory Lacrimal Glands 11 These are very small glands of exactly the same structure as the lacrimal glands. Glands of Krause—These are microscopic glands lying beneath the palpebral conjunctiva between fornix and the edge of tarsus. These are about 42 in the upper fornix and 6–8 in the lower fornix. Glands of Wolfring—These are few in number, present near the upper border, of the superior tarsal plate and along the lower border of inferior tarsus.

12. Structure, blood supply and nerve supply 12 All lacrimal glands are serous acini, similar in structure to the salivary glands. Microscopically these consist of glandular tissue (acini and ducts), connective tissue and puncta. Blood supply. Main lacrimal gland is supplied by lacrimal artery which is a branch of ophthalmic artery. Nerve supply includes: Sensory supply comes from lacrimal nerve, a branch of the ophthalmic division of the fifth nerve. Sympathetic supply comes from the carotid plexus of the cervical sympathetic chain. Secretomotor fibres are derived from the superior salivary nucleus (pons) → greater petrosal nerve → synapse at pterygopalatine ganglion → zygomatic nerve → lacrimal nerve → lacrimal gland.

13. Fluid covering the cornea and called it precorneal film. consist of three layers, which from posterior to anterior are mucus layer, aqueous layer and lipid or oily layer. 13

14. 1. Mucus layer. 14 It is the innermost and about 0.2 mm thick stratum of the tear film. It consists of mucin secreted by conjunctival goblet cells and glands of Manz. It converts the hydrophobic corneal surface into hydrophilic one.

15. 2. Aqueous layer. 15 The bulk of tear film (7.0 mm) is formed by this intermediate layer which consists of tears secreted by the main and accessory lacrimal glands. The tears mainly comprise of water and small quantities of solutes such as sodium chloride, sugar, urea and proteins. Therefore, it is alkaline and salty in taste. It also contains antibacterial substances like lysozyme, betalysin and lactoferrin.

16. 3. Lipid or oily layer. 16 This is the outermost and thinnest (0.1 mm) layer of tear film formed at air-tear interface from the secretions of meibomian, zeis, and moll glands. This layer prevents the overflow of tears, retards their evaporation and lubricates the eyelids as they slide over the surface of the globe

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19. Functions of tear film 19 Keeps moist the cornea and conjunctiva. Provides oxygen to the corneal epithelium. Washes away debris and noxious irritants. Prevents infection due to presence of anti-bacterial substances. Facilitates movements of the lids over the globe.

20. Secretion of tears Tears are continuously secreted throughout the day by accessory (basal secretion) and main (reflex secretion) lacrimal glands. Reflex secretion is in response to sensations from the cornea and conjunctiva, probably produced by evaporation and breakup of tear film. Hyperlacrimation occurs due to irritative sensations from the cornea and conjunctiva. Afferent pathway of this secretion is formed by fifth nerve and efferent by parasympathetic(secretomotor) supply of lacrimal gland. 20

21. Elimination of tears From the lacrimal gland 21 The tears flow downwards and laterally across the ocular surface. A variable amount of tears is lost by evaporation from the ocular surface. The remainder of tears flow along the superior and inferior marginal strips and collects as lacus lacrimalis in the inner canthus from where it is drained by the lacrimal passage into the nasal cavity About 70% tears is drained via inferior canaliculus and 30% via the superior canaliculus by an active lacrimal pump mechanism constituted by the fibres of orbicularis.

22. Cont… 22 With each blink, the pretarsal orbicularis oculi muscle compresses the ampullae, shortens and compresses the horizontal canaliculi, and closes and moves the puncta medially, resisting reflux. Simultaneously, contraction of the lacrimal part of the orbicularis oculi creates a positive pressure that forces tears down the nasolacrimal duct and into the nose, mediated by helically arranged connective tissue fibres around the lacrimal sac. When the eyes open, the canaliculi and sac expand, creating negative pressure that draws tears from the canaliculi into the sac.

23. Elimination of tears by lacrimal pump mechanism 23