3. 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
4. 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
5. (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
6. 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
7. 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
8. Behind the pre-corneal tear film the cornea shows
5 tissue layer’s namely
Epithelium
Bowmans layer (ant. Limiting lamina )
Stroma (substantia propria)
Decements layer (post. Limiting lamina )
endothelium
9. 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 cell’s:
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
10. 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
11. 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
12. Microvilli:
Superficial hexagonal cell folds
Stabilizes tear film
Dendritic cell :
Langerhans cells
ID and representation for lymphocytes
Absent centrally
13. 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
14. 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
15. Regularly arranged Collagen bundle
lamellae
Central (200-300)
Peripheral (500)
Proteoglycan ground and keratocytes
Lamellae – parallel, limbus to limbus
Ant. ⅓ - oblique, runs into bowman's
Deep stromal – strap like
right angles, at periphery runs into
sclera and rectus muscle
Limbus – circular course
16. 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
17. Basal lamina of endothelium
Syn. All life, from 2nd gest.
Birth – 3-4μm
Childhood - 5μm
Adult – 10-12μm
Sharply defined strong resistant sheet
Thickens – age and degen contd.
Major protein – type IV collagen
Glycoproteins +proteoglycans = pink on
acid Schiff
18. 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
19. 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
schwalbe’s line
Despite its non-elastic nature – rolls up to
stroma upon injury – resurfaces – endothelium
covers defect synth. Descement’s like basal
lamina
20. Single layer, cuboidal, hexagonal
Not vascular in origin like rest
Derived from neural crest
Young – mitosis
Birth – 6000 cells/mm²
Adult – fixed (500,000)
With age – polymerization + polymorphism
Injury – adjoining zone (area ↑*3, ht ↓)
Nuclei – flat, oval, central
21. Lateral border – convoluted-complex integration
Ant. (basal) – descement’s – HD
focal areas of inc. density - pinocytotic vesicles
Lateral memb. runs ant. and post.
Post. (apical)
Apicolateral interface marginal fold
Tight junction’s – maculae adherentes and
maculae occlundentes
Desmosomes – rare
22. 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
25.
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
26.
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
27. Maurice theory: Explained on the basis of stromal lattice
arrangement of collagen fibrils
Small diameter – regular spacing – light back scatter
suppressed – destructive interface
Goldman theory: Fibril separation and a diameter ↓ ⅓ of the
wave length of incident light – perfect transparency
Loss of transparency Corneal scaring – new collagen – irregular interweaving
Stromal – corneal oedema - ↑ spaces – fluid lakes – stromal
cloud → irregular surface viz irregular astigmatisum
Epithelial oedema: ill fit CL/ IOP → seperation of basal cells by
oedema → diffraction grating effect
Imp. Symp in sub ac. Angle closure glaucoma
28. Main function→ optics
Forms principle refracting surface ( 70% )
Factors such as Transparency
Smooth anterior surface
Uniform arrangement of epithelial cells
Closely packed stromal lamellae of uniform size
Avascularity
Help in maintaining a clear cornea
Factors that effect cornel hydration viz
transparency
corneal epithelium
corneal stroma
corneal endothelium
29. 5-7 layers, 5µm, 10% of cornea
Non-keratanized sq. epithelium – regenerating
Mech. Barrier – tight junct. ; electric resistance –
impermeable
Transparency – homogeneity
Edema – surface irregular , Vn ↓
Sympt – glare, photophobia, halos due to
scattered light
min. in mesopic condt
30. 90% of cornea, uniformly arranged collagen fibrils
Ground subs – glycosaminoglycans
keratan sulfate
dermatan sulfate
chondroitin
Stroma – water (70%), keratocytes(5%)
Role – strength and shape
Stroma+endo = preserve transparency
Stromal oedema – epi/ endo malfunction
A.P. spatial separation of ground subs
corneal diameter doesn't swell
31. Monolayer, homogeneous, hexagonal cells 5μm
Maintains transparency by
endothelial barrier function
endothelial pump mechanism
Epithelial barrier better
Barrier - cornea and aq. Compartment
Pump mech – active Na-K-ATPase
aq. Leak into stroma freed
Young – 3000-5000 cells/mm²→2/3 in adults
↓500 cells/mm² - corneal oedema
32. Transparency depends on hydration
To remain transparent – thin and dehydrated
Aq. medium – cornea swell – GAG
Dehydration –
stromal swelling pressure (SP)
barrier function, epi and endo
endothelial pump
evaporation from corneal surface
intra-ocular pressure (IOP)
33. Stroma – excised (78%) hydrated
aq. Medium (98%) hydrated
Glycosaminoglycan's – major cause of hydration
Keratan sulfate and chondroitin – electrostatic
repulsion – swelling
Collagen fibrils – cross-link– expand with
repulsion
SP (excised) – 50mmHg,
GAG imbibition of fluid by neg. pressure – IP
Excised – SP=IP ; normally IP↓ than SP due to
IOP
Thus, IP= IOP – SP ( 17 – 50 = aveg. 30-40 )
34. GAG – resist’s flow across
resistance ↓ if hydration↑ - oedema↑
no lateral flow except at limbus
35. Epithelium and endothelium – semipermeable
for flow of water and diffusion of electrolyte’s
Epi. – 200 ↑ for electrolyte’s than endo.
zonula occludes – intre-cellular spaces – sup.
Epi cells
Endo – semipermiable – small ions + water from
aq. – IOP
36. Endothelium – imp. Pump mech (active process)
Na/K-ATPase – qubain ATP inhibitor – block endo.
Fluid transport – over hydration
Bicarbonate – thgh neg electrical potential –
thiocyanate
Carbonic anhydrase – carbonic anhydrase
inhibitors – stroma to aq.
37. Evaporation of water → con. And increase
osmolarity
Hypertonicity of tears draw the water from
cornea
Readily replaced by aqueous
Aveg loss – 4%
38. Doesn't cause epi. Oedema, not associated with corneal
thickness
But, when IP is +ve i.e
IOP ↑ - SP = epithelial oedema
Eg: ↑IOP and SP normal = epi. Thickening – glaucoma
normal IP and ↓ SP = endo. Dystrophy.
