Corneal physiology & its roles.

1. CORNEAL
PHYSIOLOGY
-Riddhi Solanki
B.Optom
Aditya Jyot Institute Of
Optometry

3. Layers of cornea

4. Primarily concerned
with:
The sources of energy which
fuel the cornea’s metabolic
activity.
Corneal transparency &its
maintenance.

5. Corneal Permeability
Water
Endothelium> Epithelium
Oxygen
Derived from atmosphere
Carbon dioxide
Permeability is 7times more than
oxygen

6. Corneal permeability
& other substances
Sodium- endothelium >
epithelium 100 times
Glucose & amino
acids:metabolically active
Associated molecules
fluorescein

7. Low sodium permeability
Relatively impermeable to
water,lactic acid,amino acid,
glucose,& large molecules
Relatively impermeable to
associated and fat soluble entities

8. Role of cell junctions
Communication
Electrical coupling
Barrier to - electrolytes
- fluid
- macromolecules

9. General classification
of junctions
Occluding or tight
Adhering
Each is further divided into shape &
size of cell contact
- zonulae(belts)
- fasciae (bands)
- maculae(focal)

10. Fibronectin
Cell surface glycoprotein
Involved in cell adhesion to surfaces
Released beneath generating epithelium
Synthesized by cornea
Found in basal & apical surface of
cultured endothelium cells.

11. Oxygen supply to
cornea
It is the most important metabolite
Drives the supply from several surfaces
- atmosphere via tear film
- capillaries of the limbal region
- aqueous humor via corneal endothelium
- capillaries of palpebral conjunctiva

12. Carbon dioxide efflux
Open eye
from cornea & aqueous
humor into tear film
Closed eye
into the aqueous humor

14. Metabolism
corneal energy by
carbohydrate metabolism
Glucose enters cornea from aqueous
humor
Energy:ATP
anaerobic:breakdown of glucose into
lactic acid
aerobic: breakdown of glucose by TCA
cycle into carbon dioxide & water

15. Sources of glucose to
corneal epithelium
Aqueous humor (90%)
Limbal blood vessels & tears(less
than 10%)

16. Glucose consumption
30-90mg /hr
40-60% of total
consumption is by the
epithelium

17. Glucose metabolic pathway
EMBEDEN-MAYERHAOFF
PATHWAY
produces lactate (anaerobic)+2ATP
TRICARBOXYLIC ACID CYCLE
aerobic
HEXOSE MONOPHOSPHATE
SHUNT
aerobic produces NADPH,CO2,H2O&
6ATP

18. Lactic acid
Not metabolized by cornea
Removed by diffusion into aqueous
humor
Accumulation results in epithelial &
stromal oedema
Hypoxia doubles lactic acid
concentration resulting in an osmotic
gradient

19. CORNEAL TRANSPARENCY
Factors Affecting Corneal Transparency:
Corneal Epithelium and Tear Film
Arrangement of Stromal Lamellae
Corneal Vascularisation
Corneal Hydration

20. Corneal transparency:
stroma
Transmits 90% of incident
light
Potentially a non-
transparent layer
Fibrils: n=1.47
Ground substance: n=1.37
Regular fibril spacing :60
µm

21. Diffraction theory of Maurice
Depends on ordered arrangement of
collagen fibrils
Transparency is maintained if the
disruption is less than few wavelength
Scattering effect increases as swelling
increases(fibrils become larger
optically)

22. Corneal swelling
Lactate & metabolite accumulation-
osmotic gradient causes water
imbibition
Hydrophilicity of GAGs causes a natural
water imbibition
Swelling sleep is due to :
hypoxia (50%)
lower water osmolarity
increased temperature & humidity

23. It effects:
Change in refractive index of intra &
extracellular spaces
Sattler’s viel
haloes

24. Histochemical examination has shown
presence of the endothelium of enzymes
needed for glycolysis & krebs cycle

25. The endothelial pump

26. Drug Permiability Across
Cornea
Lipid And Water Solubility Of The Drug
Molecular Size
Weight And Concentration Of The Drugs
Ionic Form Of The Drugs