cornea m.b

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  • 1. Anatomy Dimensions Topography Histology Blood Supply Nerve Supply Physiology Functions Transparency Hydration
  • 2. The cornea is a transparent, avascular, watchglass (outer - convex and inner concave) smooth structure which forms the outer 1/6th of eye ball. Covers: iris, pupil and the anterior chamber Greek name : kerato
  • 3. Anterior surface elliptical , 11.7mm / 10.6mm Posterior surface circular , 11.7mm As V>H = astigmatism Optical zone: center Ant. Radius 7.8mm Post. Radius 6.5mm Thickness: center 0.5 to 0.6mm periphery 0.6 to 0..8 mm Refractive power : ant. Surface +48D, post. Surface -5D = +43D Refractive index: 1.37 Border: limbus
  • 4. (A) ant. & post. Diameters The diff in v and H in ant is due to conj. And sclera (B) thickness and the depth in relation to A.C and post. chamber
  • 5. Corneal shape important for contact lens fitting done by keratometry Aveg. ant surface 7.8mm to 8.4mm post surface 5.8mm Flatter in males
  • 6. Ant curvature spherical, 2-4mm decentered up and out towards visual axis but, correctly placed for pupillary aperture = corneal cap/apex Corneal curvature - limbus to apex is flattened nasally and above Corneal gutter limbus - helps in CL fitting
  • 7. Behind the pre-corneal tear film the cornea shows 5 tissue layers namely Epithelium Bowmans layer (ant. Limiting lamina ) Stroma (substantia propria) Decements layer (post. Limiting lamina ) endothelium
  • 8. Stratified, squamous and nonkeratanized nucleated cells of 5-6 layers Basal cells: deepest, palisade on the basal lamina, germinative layer Columnar with flat base, round head and oval nuclei oriented parallel to the long axis Winged/ umbrella cells: Polyhedral cells Convex ant. Cap Converging base Post. Process b/w the basal cell Nuclei parallel to corneal surface Next 2-3 layers are polyhedral cells whose base keeps inc. towards the surface Surface cells largest in area, nonkeratanized and nucleated
  • 9. Epithelial cell show cell organelles of actively metabolizing cell distributed in variable no. in different layers Mitochondria: scares in basal but, abundant in middle and winged tonofibrills : cells of electron dens cytoplasmic meshwork
  • 10. Desmosomes : adhesion Abundant basal Scarce - wing and surface Zonulae occludents + desmosomes impermeable to all but, semipermeable in bathing pre-corneal tear film Hemi-desmosomes basal cell to basal lamina
  • 11. Microvilli: Superficial hexagonal cell folds Stabilizes tear film Dendritic cell : Langerhans cells ID and representation for lymphocytes Absent centrally
  • 12. Repair : germinating layer Mitosis inhibited by injury, adrg, anesth. associated with cAMP Centripetal cell slide - actin fibrils rearranged amoeboid manner halt at inhibition mitosis resume
  • 13. Narrow, homogenous Modified zone of ant. stroma Ant- basement membrane Post- stroma Boundary- junct. b/w cornea and limbus Ultrastructure Collagen fibrils - strength Post- more progressive and blend into stroma Cannot regenerate coarse scar. Non-myelinated nerves
  • 14. Regularly arranged Collagen bundle lamellae Central (200-300) Peripheral (500) Proteoglycan ground and keratocytes Lamellae parallel, limbus to limbus Ant. - oblique, runs into bowman's Deep stromal strap like right angles, at periphery runs into sclera and rectus muscle Limbus circular course
  • 15. In each stromal lamellae collagen bundles run parallel Variation b/w the lamellar thickness C. Fibrils causes corneal transparency Keratocytes : sys. and maintain stromal collagen + proteoglycan Found b/w not in lamellae Maculae occludentas binds No ant. Post Nuclei flat, long Cytoplasm scares Cell organelle complete but few
  • 16. Basal lamina of endothelium Syn. All life, from 2nd gest. Birth 3-4m Childhood - 5m Adult 10-12m Sharply defined strong resistant sheet Thickens age and degen contd. Major protein type IV collagen Glycoproteins +proteoglycans = pink on acid Schiff
  • 17. Ant. 1/3rd - oldest produced in fetal life irregular bands, unlike type I collagen Banding 5th IUL Post. 2/3rd after birth homogenous fibro-granular material zone next to endo new Aging long spacing collagen polymerization
  • 18. Hassal-Henel Wart focal over-production of basal lamina like material aging fissured and cytoplasmic invagination on endo faces resembles descements wart/corneal guttate(fusch dyst.) Peripheral rim: landmark for corneal limbus viz schwalbes line Despite its non-elastic nature rolls up to stroma upon injury resurfaces endothelium covers defect synth. Descements like basal lamina
  • 19. Single layer, cuboidal, hexagonal Not vascular in origin like rest Derived from neural crest Young mitosis Birth 6000 cells/mm Adult fixed (500,000) With age polymerization + polymorphism Injury adjoining zone (area *3, ht ) Nuclei flat, oval, central
  • 20. Lateral border convoluted-complex integration Ant. (basal) descements HD focal areas of inc. density - pinocytotic vesicles Lateral memb. runs ant. and post. Post. (apical) Apicolateral interface marginal fold Tight junctions maculae adherentes and maculae occlundentes Desmosomes rare
  • 21. Post. Cell wall microvilli Cilia rare, to A.C., more in periphery Cell wall pinocytotic vesicles on inner surface Cell organelle: Mitochondrion - around nucleus (like RPE, and ellipsoid of R. photoreceptors) RER, SER, Golgi apparetus peri-nuclear facing A.C. Cytoplasum condens, actin rich Terminal web: close to post. Memb. ass. With location of tight junction
  • 22. Cornea is avascular Ant. Ciliary 1 mm Sub-conjuctival
  • 23. Trigeminal ophthalmic Descements and endothelium show no innervations
  • 24. Functions of cornea are : 1. 2. Transparency 3. Containing of intra-ocular pressure 4. Refraction of light Protection (corneal reflex) The collagen fibrils matrix found in the stromal layer is responsible for the containing IOP
  • 25. Transparency is due to Anatomical Avascularity Epithelial non-keratinization Stromal lamellar packing Non-myelinated nerves Pre-corneal tear film Physiological Corneal dehydration Uniform refractive index water from endothelium maintains optical homogeneity
  • 26. Maurice theory: Explaine