ANATOMY & PHYSIOLOGY OF TEAR FILM FOR CONTACT LENS FITTING.pdf
The tear film consists of three layers - mucin, aqueous, and lipid layers. The mucin layer is innermost and secreted by conjunctival goblet cells. The aqueous layer is middle layer containing proteins, immunoglobulins, and other components secreted by the lacrimal gland. The outermost lipid layer prevents evaporation and is secreted by Meibomian glands. The tear film has functions like keeping the cornea moist, providing nutrients to the cornea, washing away debris, and preventing infections. Tear secretion has two stages - secretion from the lacrimal gland either basally or through reflex tearing, and elimination via drainage through the nasal lacrimal duct when eyelids blink or open.
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ANATOMY & PHYSIOLOGY OF TEAR FILM FOR CONTACT LENS FITTING.pdf
- 1. TEAR FILM CONTENTS 1 ANATOMY 2.PHYSIOLOGY
- 2. ANATOMY OF TEARFILM Wolffirstly describedthe structureand called it as “PRE CORNEAL TEARFILM” From posterior to anterior, it consists of three layers ■ Mucin Layer ■ Aqueous Layer ■ Lipid Layer
- 3. Mucin Layer ■ Itis the innermostlayer ■ Thickess-0.2mm ■ Secreted by conjunctival goblet cells and gland of manz
- 4. Aqueous Layer ■ Middlelayer ■ Thickness-7mm ■ Secreted by main and accessorylacrimal gland ■ It contains proteins,immunoglobulin,urea,glucoseetc....
- 5. Lipid Layer ■ Outermostlayer ■Thickness-0.1mm ■ Secreted by Zeis and Moll gland ■ This layer prevents overflow of tears and evaporation
- 7. FUNCTIONS OF TEARFILM ■ Keeps the cornea and conjunctivamoist ■ Maintain corneal surfaceoptically uniform ■ Provide oxygen to the corneal epithelium ■ Washes away the debris and irritants ■ Prevent infection due to the presence of lysozyme ■ Facilitate the movementof lid over the globe
- 8. PHYSIOLOGY OF TEARFILM Tear film dynamics mainly consists of two stages; ■ Secretion of tears ■ Elimination of tears
- 9. Secretion of tears Thereare mainly two types of secretions produced by main and accessorylacrimal gland; ■ Basal secretion(Accessorylacrimal gland) ■ Reflex secretion(Main lacrimal gland) MECHANISM ■ Afferent pathway for secretion of tearfilm is contributedby fifth nerve ■ Efferent pathway for secretion is contributed by parasympathetic nerve fibers
- 11. When the eyelidclose; ■ Contraction of pretarsal orbicularis oculi ■ Compression of ampulla and shorteningof canaliculi ■ Result in movementof tear fluid from here to lacrimal sac ■ Contraction of presentation fibers of orbicularis distend the sac and create a negative pressurewhich draws tear from canaliculi to lacrimal sac
- 12. When eyelids areopen; ■ Relaxation of pretarsal orbicularis allow canaliculi and ampulla reopens and draws tear from lacus lacrimalis and marginal tear strips ■ Relaxation of preseptal fibers (Horner’s muscle)resulting in the collapse of sac and a positive pressureis created which forces the tear down to NLD into the nose ■ Gravity also helps to the draining of tears to nose
- 13. THANK YOU Have anice day