Your SlideShare is downloading. ×
Anatomy of cornea
Upcoming SlideShare
Loading in...5
×

Thanks for flagging this SlideShare!

Oops! An error has occurred.

×
Saving this for later? Get the SlideShare app to save on your phone or tablet. Read anywhere, anytime – even offline.
Text the download link to your phone
Standard text messaging rates apply

Anatomy of cornea

1,781
views

Published on

Published in: Technology, Health & Medicine

0 Comments
4 Likes
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total Views
1,781
On Slideshare
0
From Embeds
0
Number of Embeds
1
Actions
Shares
0
Downloads
102
Comments
0
Likes
4
Embeds 0
No embeds

Report content
Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
No notes for slide

Transcript

  • 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 .

×