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

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Anatomy of the Cornea: Structure and Physiology

  • 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.
  • 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
  • 7.
  • 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
  • 26.
  • 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
  • 29.
  • 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
  • 32.
  • 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 .