More Related Content
What's hot
What's hot (20)
Similar to Anatomy of cornea
Similar to Anatomy of cornea (20)
Recently uploaded
Recently uploaded (20)
Anatomy of cornea
- 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
- 4. 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
- 5. 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
- 6. STRUCTURES 5 LAYERS A nterior Epithelium Bowman’s layer C entral stroma Descemets membrane E ndothelium
- 8. 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
- 9. 2. WING or UMBRELLA cells Polyhedral Convex anteriorly 3. SURFACE CELLS 2-3 layers Polyhedral
- 10. 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
- 11. 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.
- 12. 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
- 13. Physiology of Epithelium Rich in glycogen , serves as energy store in aerobic conditions Glycogen levels Hypoxia Corneal sensitivity
- 14. 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
- 15. Markers Epithelial cells – CK3 Cells of regenerative regions (limbal, transient amplifying cells & transitional cells)- CK19 , VIMENTIN Hemidesmosome – a6b4 integrin
- 16. Repair Mitosis inhibited by 1. Injury 2. Adrenergic agents 3. Surface anesthetics
- 17. Repair occurs by CENTRIPETAL SLIDE Rearrangement of Actin fibrils Amoeboid migration Halted by CONTACT INHIBITION Anchor MITOSIS resumes until epithelial thickness is re-established
- 18. TOTAL EPITHELIAL LOSS Adjacent Conjunctival epithelium resurfaces Cornea Vascularised conjunctival type of epithelium containing GOBLET CELLS
- 19. 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
- 20. 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
- 21. STROMA 500u Regularly arranged lamellae of collagen bundles Contains keratocytes between lamellae Keratocytes – production of COLLAGEN & PROTEOGLYCANS during development
- 22. Stromal repair Keratocyte Activation Migration Transformation into Fibroblasts Requires presence of overlying epithelium
- 23. 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
- 24. 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
- 25. 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
- 27. 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
- 28. 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
- 30. 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
- 31. 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
- 33. 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.
- 34. 3. INJURY & REPAIR: Physical & chemical (ouabain) SLIDING PHENOMENA
- 35. STRUCTURAL PROTEINS OF CORNEA COLLAGEN Basal lamina - type 4 Bowman’s - 5 Stroma - 1 (90%) Descemets - 4
- 36. PROTEOGLYCANS Keratan sulphate – 50% Chondoritin sulphate Chondroitin Peripheral cornea Dermatan sulphate & Keratan sulphate
- 37. Stromal edema Altered biosynthesis of ground substance Dermatan sulphate present centrally Scarring Keratan sulphate & Heparan sulphate and Hyaluronate
- 38. 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
- 39. Other factors Absence of blood vessels & pigments Absence of myelinated nerve fibres Uniform refractive index of all layers & uniform spacing of collagen fibrils
- 40. 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
- 41. 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
- 42. Divides into 2 branches Anterior & Posterior Anterior passes subjacent to the BOWMANS forming SUBEPITHELIAL PLEXUS Posterior innervates posterior stroma , does not involve Descemets .