LACRIMAL APPARATUS.pptx LACRIMAL APPARATUS.pptx

LACRIMAL APPARATUS.pptx

1. Lacrimal Apparatus G K K M Optom Asst.Prof MLRU

2. LACRIMAL APPARATUS The lacrimal apparatus comprises the structures concerned with the formation of tears (the main lacrimal gland and accessory lacrimal glands)and its transport. The lacrimal passage includes: Puncta Canaliculi Lacrimal sac Naso-lacrimal duct .

3. LACRIMAL GLANDS Main lacrimal gland The main lacrimal gland is situated in the fossa for lacrimal gland, formed by the orbitalplate of frontal bone, in the antero -lateral partof the roof of orbit. The gland is divided into two parts: Superior orbital Inferior palpebral

4. The orbital part of lacrimal gland : It is large, about the size and shape of a small almond. It has two surfaces (superior and inferior), two borders (anterior and posterior) and two extremities (medial and lateral). Superior surface of the orbital part is convex and lies in contact with the periorbita lining the part of the frontal bone forming the fossa for the lacrimal gland. Inferior surface of the orbital part is concave and lies on the levator palpebrae superioris muscle and the lateral horn of the levator aponeurosis . Anterior border is sharp and seems within and parallel to the orbital margin, up to the zygomatico -frontal suture. It lies in contact with the septum orbitale . Posterior border is round and becomes continuous with the palpebral part of the gland. It lies in contact with the orbital pad of fat. Lateral extremity rests on the lateral rectus muscle. Medial extremity is related to the levator palpebrae superiors muscle

5. Palpebral part of lacrimal gland It is small (about one-third the size of orbitalpart ) and consists of only two or three lobules. It is situated upon the course of the ducts of orbital part from which it is separated by the levator palpebrae superioris muscle, which isrelated to it superiorly. Inferiorly, the gland lies in relation to the superior fornix. The gland is compressed from above to downwards and can be seen through the conjunctiva when the upperlid is everted . Posteriorly , it is continuous with the orbital part.

6. Ducts of lacrimal gland About 10-12 ducts pass downwards from the main lacrimal gland to open in the lateral part of the superior fornix. One or two ducts also open in the lateral part of the inferior fornix. Since all the ducts pass through the palpebral part of the gland, therefore, excision of the palpebral part alone amounts to excision of the entire gland as far as the secretory function of the gland is concerned.

7. Histological structure of the lacrimal gland Lacrimal gland is a branched tubulo -alveolar (serous acinous ) gland, similar in structure like salivary glands. Microscopically, it consists of glandular tissue, stroma and septa .It passes no true capsule but is surrounded by periorbita as the outermost limit. Glandular tissue consists of acini and ducts arranged in lobes and lobules, separated from each other by the fibro-vascular septa.

8. Acini are lined by a single layer of pyramidal cells mounted on a basement membrane. The pyramidal cells are of the serous type with eosinophilic secretory granules and a round nucleus situated towards the base. These cells secrete the tears, expelled by the contraction of myofibrils. Ductules and ducts. The secretion of the acinar units is drained by connecting channels which to begin with are intralobular , then these become extralobular and lastly open in the ducts. The ducts are lined by two layers of epithelial cells the inner lining is formed by thick cylindrical cells and the outer layer is of flattened cells. Stroma of the lacrimal gland It is formed by mesodermal tissue which contains connective tissue, elastic tissue, lymphoid tissue, plasma cells, rich nerve terminals and blood vessels.

9. Blood supply Arterial supply. Main lacrimal gland is supplied by lacrimal artery, a branch of ophthalmic artery. Sometimes a branch of the transverse facial artery may also supply the gland Lacrimal veins draining the gland join the ophthalmic vein. Lymphatic drainage The lymphatic drainage is along the conjunctival drainage into the preauricular lymph nodes.

10. Nerve supply Main lacrimal gland has three modes of innervations Sensory nerve supply comes from the lacrimal nerve, a branch of ophthalmic division of the fifth cranial nerve. Sympathetic nerve supply arises from the superior cervical sympathetic ganglion as postganglionic fibres which from the carotid plexus of the cervical sympathetics . From the sympathetic plexus around the internal carotid artery, some fibres join the deep petrosal nerve, then the nerve of pterygoid gland, and then ultimately reach the lacrimal gland through the lacrimal nerve branch of V 3. Secretomotor fibres are derived from the superior salivary nucleus. The course of the nerve fibres reaching the lacrimal gland in summarized as below: Lacrimatory nucleus ( pons ) Zygomatic nerve(postganglionic fibres ) Zygomatico-facialbranch Lacrimal nerve Lacrimal gland.

11. Accessory lacrimal glands Glands of Krause • Glands of Wolfring • Intraorbital glands • Glands in the caruncle and plica semilunaris Glands of Krause. These are microscopic glands lying in the sub- conjunctival tissue of the foraices . These are about 40-42 in the upper fornix and about 6-8 in the lower fornix. Their ducts unite to form a long duct which opens in the fornix. Glands of Wolfring These are microscopic glands present along the upper border of superior tarsus (2-5 in number), and lower border of inferior tarsus (2-3 in number) Rudimentary accessory lacrimal glands : These are present in the caruncle , plica semilunaris and infraorbital region.

12. LACRIMAL PASSAGES Lacrimal Puncta Lacrimal Canaliculi Lacrimal sac Naso Lacrimal Duct (NLD)

13. Lacrimal puncta These are two small rounded or oval openings one each on the upper and lower eyelids, at the junction of ciliary and lacrimal portion of the lid margin . Each punctum is situated upon a slight elevation called lacrimal papilla, which becomes prominent in old age. The upper and the lower puncta lie about 6 mm and 6.5mm lateral to the inner canthus , respectively. Thus when the eyelids are closed, the puncta do not overlap each other, but the upper punctum lies medial to the lower punctum . The upper punctum is directed downwards and backwards, while the lower punctum is directed upwards and backward. Normally, the puncta are not visible unless the lids are everted . The puncta are surrounded by a ring of dense fibrous tissue which keeps them patent .

14. 2. Lacrimal canaliculi The superior and inferior canaliculi join the puncta to the lacrimal sac. Each canaliculus is 0.5 mm in diameter and has two parts, vertical(2 mm) and horizontal (8 mm), which lie at right angles to each other. At the junction of the two portions, there is slight dilatation called the ampulla . The horizontal part of each canaliculus converges towards the medial canthus . Each canaliculus pierces the larcimal fascia ( periorbita covering the lacrimal sac)separately and then unite to form a common canaliculus which opens in a small diverticulum of sac called the lacrimal sinus of Maier. The point of opening into the sac lies at the middle of the lateral surface of the sac about 2.5 mm from its apex.

15. 3. Lacrimal sac Location. It lies in the lacrimal fossa located in the anterior part of medial orbital wall. Dimension. The lacrimal sac when distended is about 15 mm in length and 5-6 mm in breadth. It has three parts: Fundus -portion above the opening of canaliculi (3-5 mm); Body-middle part (10-12 mm); Neck (lower small part which is narrow and continues with the naso lacrimal duct)

16. 3. Nasolacrimal duct (NLD) It continues downward from the neck of the lacrimal sac to its opening in the inferior meatus of the nose. It is about 18 mm (may vary from 12-24 mm) in length and about 3 mm in diameter. The upper end of the NLD is its narrowest part. Direction of the NLD is downwards, backwards and laterally. Externally, its location is represented by a line joining inner canthus with the ala of nose. It consists of two parts: an intra osseous part (12.5 mm)and an intra- meatal part (5.5 mm). The intraosseous part lies in the bony nasolacrimal canal which is formed antero -laterally by the maxilla and posteromedially by the lacrimal and inferior nasal concha . The nasolacrimal canal lies lateral to middle meatus and produces a ridge in the maxillary antrum ; therefore, lesions of the maxillary sinus often cause epiphora . Intra- meatal part of the NLD lies within the mucous membrane of the lateral wall of the nose.

17. The opening of the NLD in the inferior meatus is situated at a depth of about 30-40 mm from the anterior nares . The lumen of the NLD is marked by numerous folds of mucous membrane, the so-called valves. Of these, the most consistent and important one is valve of Hasner situated at its lower end.

18. VESSELS AND NERVES Blood supply of the lacrimal passages Arterial supply - superior and inferior palpebral arteries (branches of ophthalmic artery), angular artery, infraorbital artery and nasal branches of spheno -palatine artery. Venous drainage occurs into the angular vein and infra-orbital vein from above and into the nasal vein from below. Nerve supply Sensory nerve supply to the lacrimal sac and ND comes from the infra- trochlear nerve and the anterior superior alveolar nerves .