The Lacrimal Apparatus
The lacrimal apparatus consists of two divisions. The first is the secretory part, which is responsible for the production of tears, and the second is the drainage part. The secretory part contains the main lacrimal gland, which is lodged in a fossa in th
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The Lacrimal Apparatus
Keywords
Lacrimal apparatus Secretory parts Drainage parts Main lacrimal gland Accessory lacrimal glands of Krause and Wolfring Tear film Lysozyme Superior and inferior puncta Vertical and horizontal canaliculi Medial canthus Lacrimal sac Nasolacrimal duct Inferior meatus of nose Delayed canalization of nasolacrimal duct Epiphora Lacrimation
The lacrimal apparatus consists of two divisions. The first is the secretory part, which is responsible for the production of tears, and the second is the drainage part. The secretory part contains the main lacrimal gland, which is lodged in a fossa in the lateral part of the roof of the orbit, and two accessory lacrimal glands of Krause and Wolfring. The latter are present near the fornix. They are often called basal secretors because normally their secretions are sufficient to serve the purpose for which tears are meant without any need of drainage to the nose. The main lacrimal gland is brought into action when there is severe emotional stress or physical irritation caused by inflammation in the anterior segment of eye, causing an increase in the amount of secretion and a possible need for drainage to the nose. The afferent path for that reflex is via the ophthalmic division of the trigeminal nerve and the efferent path via the facial nerve. The main lacrimal gland is divided into a larger orbital and a smaller palpebral part by the lateral horn of the
aponeurosis of the levator palpebrae superioris. The secretory ducts reach the lateral part of the superior fornix. One or two ducts may open directly into the inferior fornix. The tear film has three layers. The outermost is the lipid layer from the meibomian glands which regulates the evaporation from the surface of the cornea and conjunctiva and prevents the spilling of tears on the face. The middle layer is aqueous, having soluble minerals and proteins that originate in the main and accessory lacrimal glands. The third innermost layer is mucoid and comes from the goblet cells of the conjunctiva. It contains glycoprotein mucin. The tears have many functions. (1) They make the corneal surface smooth by covering the microscopic irregularities of the corneal epithelium, which is essential for adequate refraction at the cornea. (2) They keep the corneal and conjunctival surfaces moist for normal function. (3) They provide nutrition to the corneal and conjunctival epithelia. (4) They catch flying dust
© Springer International Publishing Switzerland 2016 M.W. Ansari and A. Nadeem, Atlas of Ocular Anatomy, DOI 10.1007/978-3-319-42781-2_7
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particles and send them along the tear streak at the posterior sharp border of the lid margin. (5) They inhibit the growth of microorganisms by the antimicrobial action of lysozyme. (6) The constant evaporation of the tear film from the surface of cornea and conjunctiva takes heat from the conjunctival sac, allowing its temperature to be lower than that of other parts of body. This low temperature does not allow multipli
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