Cornea - 1

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  • Cornea - 1

    1. 1. CORNEA
    2. 2. CORNEA <ul><li>Transparent, </li></ul><ul><li>Avascular, </li></ul><ul><li>Principle optical surface of the eye </li></ul><ul><li>Forms anterior one-sixth of the outer fibrous coat of the eyeball. </li></ul>
    3. 3. Dimensions <ul><li>Anterior surface </li></ul><ul><li>Elliptical shape </li></ul><ul><li>Horizontal diameter:11.75 mm </li></ul><ul><li>Vertical diameter :10.6 mm </li></ul><ul><li>Posterior surface </li></ul><ul><li>circular shape </li></ul><ul><li>average diameter : 11.75 mm </li></ul>
    4. 4. <ul><li>Thickness </li></ul><ul><li>at centre : 0.52 mm </li></ul><ul><li>at periphery : 1.2 mm </li></ul><ul><li>Radius of Curvature </li></ul><ul><li>central 5 mm of the cornea forms powerful refracting surface of the eye. </li></ul><ul><li>Anterior : 7.8 mm </li></ul><ul><li>Posterior : 6.5 mm </li></ul><ul><li>Refractive power </li></ul><ul><li>45 diopters </li></ul><ul><li>3/4 th of the total refractive power (60 D) </li></ul><ul><li>Refractive Index </li></ul><ul><li>1.376 </li></ul>
    5. 5. Histology
    6. 6. Histology
    7. 7. Epithelium
    8. 8. Bowman's membrane <ul><li>Acellular mass of condensed collagen fibrils </li></ul><ul><li>Thickness : 8 – 14 microns </li></ul><ul><li>Shows considerable resistance to infection and injury </li></ul><ul><li>But once destroyed, does not regenerate </li></ul>
    9. 9. Stroma <ul><li>Thickness : 0.5 mm </li></ul><ul><li>90 % of total corneal thickness </li></ul><ul><li>Consists of collagen fibrils (lamellae) and cells embedded in hydrated matrix of proteoglycans (ground substance). </li></ul><ul><li>Lamellae arranged parallelly (200 – 250 layers) </li></ul><ul><li>Cells : keratocytes </li></ul>
    10. 10. Descemet`s membrane <ul><li>Represents the basement membrane of the endothelium </li></ul><ul><li>Made up of collagen and glycoprotein </li></ul><ul><li>Thickness :10-12 µm </li></ul><ul><li>Very resistant to chemical agents, trauma, infection and pathological processes. </li></ul><ul><li>Maintains integrity of the eyeball </li></ul><ul><li>It can regenerate, when destroyed. </li></ul>
    11. 11. Endothelium <ul><li>Single layer of flat hexagonal cells. </li></ul><ul><li>Mosaic pattern </li></ul><ul><li>Cell density : 2400 3000 cells/mm2 </li></ul><ul><li>Contains active pump mechanism </li></ul><ul><li>Best evaluated by specular microscopy </li></ul>
    12. 12. Limbus <ul><li>Anatomically the limbus refers to circumcorneal transitional zone of the conjunctivo-corneal and corneo-lscleral junction. </li></ul>
    13. 13. Blood & Nerve supply <ul><li>Blood supply </li></ul><ul><li>Avascular structure </li></ul><ul><li>Small loops derived from the superficial and deep plexus, invade its periphery for about 1mm and provide nourishment </li></ul><ul><li>Nerve supply </li></ul><ul><li>Has rich sensory supply </li></ul><ul><li>Long ciliary nerves branches of nasociliary nerve (a branch of ophthalmic division of trigeminal nerve) </li></ul><ul><li>Non myelinated </li></ul>
    14. 14. Development of the cornea <ul><li>Epithelium : surface ectoderm </li></ul><ul><li>Bowman`s layer, stroma , Endothelium & descemet`s membrane : mesenchymal cells derived from neural crest. </li></ul>
    15. 15. Corneal physiology <ul><li>Two primary physiologic functions </li></ul><ul><li>Act as a powerful refracting medium, transmits light in an orderly fashion for proper image formation. </li></ul><ul><li>Protects intraocular contents. </li></ul>
    16. 16. Corneal physiology
    17. 17. Corneal transparency <ul><li>Anatomic / physical factors </li></ul><ul><li>Uniform and regular arrangement of corneal epithelium </li></ul><ul><li>Regular arrangement of stroma </li></ul><ul><li>Corneal avascularity, non myelinated nerve fibres </li></ul><ul><li>Normal tear film </li></ul><ul><li>Physiological factors </li></ul><ul><li>Relative state of corneal dehydration </li></ul><ul><li>Stromal swelling pressure </li></ul><ul><li>Normal intraocular pressure </li></ul><ul><li>Endothelial pump mechanism </li></ul>
    18. 18. Tear film <ul><li>Three layers </li></ul><ul><li>Mucus layer : innermost & thinnest </li></ul><ul><li>0.02 -0.05 microns </li></ul><ul><li>secreted by conjunctival goblet cells </li></ul><ul><li>Aqueous layer : thickest </li></ul><ul><li>6.5 – 7.5 microns </li></ul><ul><li>secreted by main & accessory lacrimal glands </li></ul><ul><li>Alkaline & antibacterial </li></ul><ul><li>Lipid or oily layer : outermost </li></ul><ul><li>0.1 microns </li></ul><ul><li>secreted by meibomian, zeis & moll glands. </li></ul>
    19. 19. Functions of the tear film <ul><li>Keeps the cornea & conjunctiva moist </li></ul><ul><li>Provides oxygen to the cornea </li></ul><ul><li>Washes away debris & noxious irritants </li></ul><ul><li>Prevents infection due to presence of antibacterial substances </li></ul><ul><li>Facilitates smooth movements of the lids over the globe </li></ul>
    20. 20. CONGENITAL ANOMALIES <ul><li>Microcornea : horizontal diameter </li></ul><ul><li>< 10 mm since birth. </li></ul><ul><li>Megalocornea : horizontal diameter of the cornea is of adult size or 13 mm . </li></ul>
    21. 21. CONGENITAL ANOMALIES <ul><li>Cornea plana : cornea is comparatively flat </li></ul><ul><li>since birth. </li></ul><ul><li>Congenital cloudy cornea </li></ul>
    22. 22. Keratitis <ul><li>Any type of corneal inflammation –Keratitis </li></ul><ul><li>Types – </li></ul><ul><li>superficial –ant to Bowman’s membrane </li></ul><ul><li>Deep –stromal or interstitial or endothelitis </li></ul>
    23. 23. Few terminologies <ul><li>Abrasion-defect in the epithelium </li></ul><ul><li>Corneal ulcer-defect in the epithelium+inflammation+surrounding tissue necrosis. </li></ul><ul><li>Corneal scar or opacity-healing of any corneal injury beyond the level of bowman’s membrane </li></ul><ul><li>Types-nebula, macula and leucoma </li></ul>
    24. 25. <ul><li>Corneal edema </li></ul><ul><li>Keratic precipitates-deposition of leucocytes on the back of cornea </li></ul><ul><li>Hypopyon </li></ul>

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