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Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
Anatomy of cornea
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Anatomy of cornea

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  • 1. ANATOMY OF CORNEA Dr Nithin Keshav
  • 2. Introduction CORNEA – Medieval Latin “ co rne a te la “ HORNY WEB (latin ,cornu = horn)  Transparent avascular tissue with a convex anterior surface & concave posterior surface.  Main function is OPTICAL  Accounts for 70% of the total refractive power of the eye (+ 43D)  Other functions are: -STRUCTURAL INTEGRITTY -PROTECTION FOR
  • 3. DIMENSIONS  Anterior Surface : Vertical – 11.7 mm Horizontal – 10.6 mm  Posterior Surface : Both 11.7 mm  Thickness : Central 0.52 mm Peripheral 0.67 mm  Surface Area: 1.3 cm2
  • 4.  Radius of Curvature Anterior – 7.8 mm Central 1/3 Posterior – 6.5 mm - Peripheral cornea is more flattened  Topography Anterior curvature is spherical in 2-4 mm zone decentered upwards & outwards relative to visual axis but centered to the pupillary aperture( lies 0.4 mm temporally) -- CORNEAL CAPorAPEX  Curvature varies from apex to limbus , greater
  • 5. STRUCTURES 5 LAYERS A nterior Epithelium Bowman’s layer C entral stroma Descemets membrane E ndothelium
  • 6. EPITHELIUM  Stratified , Squamous & Non Keratinized  Continuous with conjunctiva , but no goblet cells  50-90 u  5-6 layers Posterior to anterior 1. BASAL CELLS  Arranged in pallisade manner  Germinative layer  Columnar with an oval nucleus
  • 7. 2. WING or UMBRELLA cells  Polyhedral  Convex anteriorly 3. SURFACE CELLS  2-3 layers  Polyhedral
  • 8. Ultrastructural features  Abundant mitochondria in wing & middle cell layers  High glycogen content (Wing & Superficial layers)  Tonofibrils ( Intermediate filaments)  Desmosomes- lateral adhesion b/w cells, mainly at the basal level.  Zona Occludens- Tight jn seen at surface cells
  • 9.  Tight jn are impermeable to Na ions & confer semipermeable membrane properties to the epithelium  Surface cells contain MICROVILLI & MICROPLICAE– Helps in stabilizing precorneal tearfilm  Dendritic cells ( langerhans cells )- present in fetal epithelium but disappears in mature cornea.
  • 10. BASAL LAMINA  2 LAYERS  Superficial LAMINA LUCIDA  Deep LAMINA DENSA  Thicker peripherally  Thickened in Diabetes , Corneal pathology, Old age  Integrated with the underlying Bowmans layer through ANCHORING FILAMENTS & ANCHORING PLAQUES  Cohesion between Basal Lamina & Bowman’s loosened by  Lipid solvents 
  • 11. Physiology of Epithelium  Rich in glycogen , serves as energy store in aerobic conditions Glycogen levels  Hypoxia Corneal sensitivity
  • 12. Turn Over  Limbal stem cells migrate towards centre  XYZ Hypothesis : Lim bal& Co rne albasale pithe lialce lls are so urce fo r CO RNEAL EPITHELIAL CELLS  TRANSIENT AMPLIFYING CELLS : Daughter cells of limbal stem cells  TRANSITIONAL CELLS: Basal cells lying between limbus & peripheral cornea commonly seen at Superior Cornea
  • 13. Markers  Epithelial cells – CK3  Cells of regenerative regions (limbal, transient amplifying cells & transitional cells)- CK19 , VIMENTIN  Hemidesmosome – a6b4 integrin
  • 14. Repair  Mitosis inhibited by 1. Injury 2. Adrenergic agents 3. Surface anesthetics
  • 15.  Repair occurs by CENTRIPETAL SLIDE Rearrangement of Actin fibrils Amoeboid migration Halted by CONTACT INHIBITION Anchor MITOSIS resumes until epithelial thickness is re-established
  • 16. TOTAL EPITHELIAL LOSS Adjacent Conjunctival epithelium resurfaces Cornea Vascularised conjunctival type of epithelium containing GOBLET CELLS
  • 17. BOWMAN’S  Aka Anterior Limiting Lamina  8-14 u  Modified region of anterior stroma  Acellular homogenous zone  Normally attached to Basal Lamina  In pathological conditions  Corneal edema , Dystrophy  After death -Epithelium readily seperates from this layer
  • 18. Ultrastructural features  Fine collagen fibrils of uniform size in ground substance  Relatively resistant to trauma (mechanical & infective)  Convex ridges can be seen when relaxed – POLYGONAL /CHICKEN WIRE PATTERN  Responsible for Anterior Corneal Mosaic  In Pro lo ng e d Hypo to ny & Atro phic Bulbi degenerative changes in the ridges contributes to Secondary Anterior Crocodile Shagreen
  • 19. STROMA  500u  Regularly arranged lamellae of collagen bundles  Contains keratocytes between lamellae  Keratocytes – production of COLLAGEN & PROTEOGLYCANS during development
  • 20. Stromal repair Keratocyte Activation Migration Transformation into Fibroblasts  Requires presence of overlying epithelium
  • 21. DESCEMET’S  Aka Posterior Limiting Lamina  2.2- 4.5 u  It is Basal Lamina of Endothelium  Appears at 2nd month of gestation  Strong resistant sheet  Sharply defined & the plane of seperation is used in LAMELLAR KERATOPLASTY  Thickens with age , endothelial degenerations  Type 4 collagen
  • 22.  Anterior 1/3 :  Oldest  Irregular banded pattern in cross section  Banding develops at 5th month IUL  POSTERIOR 2/3:  Formed after birth  Homogenous fibrillogranular material
  • 23.  In Endothelial diseases where morphology & thickness of Descemets is altered , presence of no rm alante rio r bande d laye r can be used to signify o nse t o f diso rde r afte r birth.  In AGEING CORNEA:  Bands of long spacing collagen found  Focal overproduction of basal lamina like material produces peripheralexceresences HASSAL HENLE WARTS
  • 24.  Physiological  Resemble Descemet’s warts of central cornea – CORNEA GUTTATA in Fuch’s  Peripheral rim of Descemets forms internal landmark of corneal limbus & marks anterior limit of angle – SCHWALBE’S LINE  Prominent in 15-20% of individuals
  • 25.  Hypertrophied in congenital anomalies – POSTERIOREMBRYOTOXON  On stripping Descemet’s it ROLLS INTO STROMA  Lens capsule curls outwards  On injury endothelial cells resurfaces & deposits Basal Lamina identical to Descemets
  • 26. ENDOTHELIUM  Single layer of hexagonal / cuboidal cells  Counts  At birth : 6000/mm2  1 yr : falls by 26%  11yr : another 26%  Gradual decrease in density & increase in shape variation – POLYMEGATHISM
  • 27. Ultrastructural features  Lateral borders convoluted forming marked interdigitation  Cell junction  Ant 2/3 : Maculae adherentes  Post 1/3 : maculae occludentes  Posterior surface shows Microvilli - Absorptive surface area  Abundant mitochondria  Condensation of cytoplasm rich in actin lies close to posterior membrane – TERMINAL WEB
  • 28. PHYSIOLOGY 1. NUTRITION :  Glucose & aa 2. FLUID REGULATION:  Maintains relative deturgescence by 1. Provides barrier to prevent ingress of salt & metabolites into stroma 2. Decreases osmotic pressure of stroma by active pumping out of bicarbonate.
  • 29. 3. INJURY & REPAIR:  Physical & chemical (ouabain)  SLIDING PHENOMENA
  • 30. STRUCTURAL PROTEINS OF CORNEA COLLAGEN Basal lamina - type 4 Bowman’s - 5 Stroma - 1 (90%) Descemets - 4
  • 31. PROTEOGLYCANS Keratan sulphate – 50% Chondoritin sulphate Chondroitin  Peripheral cornea Dermatan sulphate & Keratan sulphate
  • 32. Stromal edema  Altered biosynthesis of ground substance  Dermatan sulphate present centrally Scarring  Keratan sulphate & Heparan sulphate and Hyaluronate
  • 33. CORNEAL TRANSPARENCY  MAURICE THEORY: LATTICE ARRANGEMENT of collagen fibres is responsible for transparency.  Due to small diameter & regular seperation of collagen, back scattered light would be suppressed by DESTRUCTIVE INTERFERENCE  GOLDMAN THEORY : If fibril seperation & diameter is less than 1/3 of wavelength of incident light –TRANSPARENCY ensues
  • 34. Other factors  Absence of blood vessels & pigments  Absence of myelinated nerve fibres  Uniform refractive index of all layers & uniform spacing of collagen fibrils
  • 35.  In ill fitting contact lenses & IOP, basal cells which are regularly arranged are seperated by edema fluid of differing refractive index to cells DIFFRACTION GRATING EFFECT HALOS AROUND LIGHT
  • 36. NERVE SUPPLY  Ophthalmic division of Trigeminal via Anterior Ciliary Nerve  Supply also from Cervical Sympathetic  Anterior ciliary nerve enters sclera from perichoroidal space just behind the limbus & joins with the conjunctival nerve to form PERICORNEAL PLEXUS
  • 37.  Divides into 2 branches Anterior & Posterior  Anterior passes subjacent to the BOWMANS forming SUBEPITHELIAL PLEXUS  Posterior innervates posterior stroma , does not involve Descemets .

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