Everything about corneal physiology

1. Physiology of
Cornea
Dr. Tukezban Huseynova
Eye – Dr. Tuti
Apical cells
Small light
cells (young
cells)
Dark cells
(mature cells)

2. Part 1

3. I. EPITHELIUM

4. Epithelium,
5-7 cells layers
Apical Cells,
3-4 cells layer
Wing cells,
1-3 cells layer
Basal cells,
1 cells layer

5. Apical cells
These cells finally degenerate and are
sloughed from the corneal surface
vThis process results
In turnover of the entire
Epithelium every
7 days
Basal cells
Wing cells

6. Apical cells
Small light
cells (young
cells)
Dark cells
(mature cells)

7. Wing cells

8. Basal cells
Major keratin pair
K3 & K12
Minor keratin pair
K14 & K5
! The basal cell are distinguished from
limbal stem cells by the expression
of major Keratin pair

9. Basement Membrane
vLamina Lucida (anteriorly, 23nm)
vLamina densa (apposed to Bawmen’s layer)
vReticular lamina (within to Bawmen’s layer)

10. Cell Adhesion in the Epithelium

11. Cell Adhesion in the Epithelium

12. Cell Adhesion in the Epithelium
Junctional complexes of the cornea
Gap junction Tight junction

13. Limbus
Limbal epithelium
0.5 – 1 mm
Basal layer
Nonkeratinized, stratified
squamous corneal cells
Lies in superficial corneal
epithelial layers
Terminal
differentiated cells
Lies in the suprabasal layers
Postmitotic cells
Transient amplifying cell
Migrate centrally within
cornea to occupy its basal
layer
64-kD keratin
expression
Stem cells
Devision or Defferentiation
Maintenance of the Corneal epithelium

14. Maintenance of the Corneal epithelium
Y Y
X
X + Y = Z
Z
X, Y, Z Hypothesis of corneal epithelial maintenance.
X - proliferation of basal cells
Y - centripetal movement of cells
Z - cell loss from the surface

15. Epithelium wound healing
Injury Latent Phase
Cell migration
Cell proliferation
Cell adhesion
3 steps of corneal healing

16. Epithelium wound healing
Transient Amplifying cells (TA)
Step 1: Cell migration

17. Epithelium wound healing
Step 2: Cell proliferation
Limbal Stem Cells
Migration
Proliferation
and movement
toward surface
Migration

18. Epithelium wound healing
Fonte: João Alfredo Kleiner DVM, MSc
Clinical Case
Patient: 11 y.o., female
Complaints: severe ocular
pain in the right eye
Diagnosis: superficial
traumatic ulcer
Treatment: topical antibiotics,
artificial tears
clockwise vortex (whorl pattern)

19. Epithelium wound healing
Hurrycane keratopathy

20. Epithelium wound healing
Step 3: Cell adhesion
Migratory epithelial cells
Basal Lamina
Adhesion plaqes

21. Clinical Manifestation of Abnormalities in
Epithelium structure
v Epithelial basement
membrane dystrophy
(dot changes)
v Epithelial basement
membrane dystrophy
(fingerprints changes)

22. The main corneal biochemical components
ü Fibronectin–integrin
system
Epithelial movement

23. The main corneal biochemical components
ü Fibronectin–integrin
system
Epithelial movement
ü Hyaluronan

24. The main corneal biochemical components
ü Fibronectin–integrin
system
Epithelial movement
ü Hyaluronan
ü Proteolytic enzymes

25. The main corneal biochemical components
ü Fibronectin–integrin
system
Epithelial movement
ü Hyaluronan
ü Proteolytic enzymes
Cytokines and growth factors
ü Epidermal growth factor

26. The main corneal biochemical components
ü Fibronectin–integrin
system
Epithelial movement
ü Hyaluronan
ü Proteolytic enzymes
Cytokines and growth factors
ü Epidermal growth factor
ü Transforming growth factor-β

27. The main corneal biochemical components
ü Fibronectin–integrin
system
Epithelial movement
ü Hyaluronan
ü Proteolytic enzymes
Cytokines and growth factors
ü Epidermal growth factor
ü Transforming growth factor-β
ü Basic fibroblast growth factor (bFGF)

28. The main corneal biochemical components
ü Fibronectin–integrin
system
Epithelial movement
ü Hyaluronan
ü Proteolytic enzymes
Cytokines and growth factors
ü Epidermal growth factor
ü Transforming growth factor-β
ü Basic fibroblast growth factor (bFGF)
ü Interleukins

29. Part 2

30. II. BOWMAN’S LAYER

31. Modified region of anterior stroma
Characteristics
Thickness is 8 – 14 μm
Acellular homogeneous zone
It lacks fibroblast therefore after injury it is unable to regenerate-
replaced by course scar tissue
Anterior surface of this layer is smooth
The collagen fibres in Bowman's layer are
synthesized and secreted by stromal
keratocytes

32. Prevents keratocytes metaplasia to fibroblast and scar formation
Anchoring site for epithelial cells to ensure stability
Function
Prevents stromal keratocytes from exposure to epithelial growth
factors
Tough acellular layer provide mechanical supports
E – Epithelium
S – Stromal Stromal collagen fibers
B – Bowman's layer
Bar = 2 μm

33. III. STROMA

34. Stromal Structure
Made up of 200 – 250 lamellas of collagen fibers
The lamellas formed of bundles of collagen fibers
They stretch from limbus to limbus
At the limbus they turn and run circumferentially forming an
annulus 1.5 to 2.0 mm wide around the cornea (which maintains
the curvature of the cornea)
This has profound implication for possible alterations of stromal structure
during refractive or cataract surgery that may lead to possible refractive errors

35. Stromal Structure

36. Proteoglycans
The extrafibrillar material sometimes called the Ground Substance of the
stroma, is largely made up of
CD/DS
Decorin (type IV)
is the only CD/DS proteoglycan in the cornea.
More abundant in the anterior cornea than
in the posterior.
KS
More abundant in the posterior stroma.
ü Lumican
ü Keratocan
ü Mimecan
v CD/DS - chondroitin sulfat/dermatan sulfat
v KS - keratan sulfat

37. Proteoglycans
Function
Confer hydrophilic properties of stroma
Maintains corneal transparency
Helps in regular spacing of collagen fibers to ensure transparency

38. Keratocytes
Cellular component of the corneal stroma
Turn over every 2 to 3 days
Synthesize collagen
The cells are activated when the stroma is damaged
Differentiate into fibroblast during wound healing
There is a gap junction between cells

39. Corneal Transparency and Stromal Function
Interwoven fibrous collagen
The regular arrangement of collagen
mechanical strength
transparency of this tissue
Fibers of regular diameter
Interfibrillar distance less than a Wavelength of light
Avascularity
Relative dehydration

40. Interactions between Proteogycans and Collagen in the Stroma
Granular Dystrophy

41. Interactions between Proteogycans and Collagen in the Stroma
Granular Dystrophy
Lattice Dystrophy

42. Interactions between Proteogycans and Collagen in the Stroma
Granular Dystrophy
Lattice Dystrophy
Macular type 1 Dystrophy

43. Stromal Wound healing

44. Part 3

45. IV. DESCEMET’S LAYER

46. A The anterior part 3mm
P The posterior part which is secreted
after birth
Thickness
Note! There is a distinct structural difference
between fetal & postnatal components
at birth: 3 – 4 µm
at childhood: about 5 µm
at adult: 10 – 12 µm

47. Hassal-Henle warts
Descemet’s membrane abnormalities

48. Hassal-Henle warts
Corneal Guttata
Descemet’s membrane abnormalities

49. Hassal-Henle warts
Corneal Guttata
Descemet’s membrane abnormalities
Posterior
Embryotoxon

50. Spreading endothelial cells
Descemet’s wound healing
Injury
Synthesis of fresh
basal lamina

51. V. ENDOTHELIUM

53. Endothelial Cell Dencity, ECD
At birth:
about 6000 cells/mm²
At adults:
about 2500 cells/mm²

54. Endothelial Cell Dencity, ECD
The "+" indicates a larger cell, the "-" indicates
a smaller cell, and the numbers indicate the
number of sides forming the cell

55. Ultrastructural features
3-D view of deep cornea
showing
part of endothelium, DM,
Stroma

56. Nutrition of Endothelium
Endothelium gets its nutrition & O₂ from aqueous
Essential nutrients (such as glucose & amino acids) pass across its
surface to supply the cellular needs of all the corneal layers

57. Fluid regulation of Endothelium
Providing a barrier function to the ingress of salt and metabolites
to the stroma
Actively reducing the osmotic pressure of stroma by metabolically
pumping the bicarbonate ions out of the stroma to aqueous
The state of relative clearence of stroma is maintained by this delicate
monolayer of cells by two ways

58. Endothelial Repair
Physical & chemical damage to endothelium results in loss of cells
Neighbor cells move over to fill the gap by sliding process and
enlargement of cells occur
Thus, after injury, the endothelial cell density falls, the cell area
increases and the cell height decreases

59. Thank you
Eye_dr_tuti
Eye_dr_tuti