Corneal anatomy & physiology in brief with help of diagrammatic representation.

1. The Cornea
Dr. Manish Soni
Dr. S. N. Medical College
Jodhpur (Raj.)

2. The eye
A Fused Two Piece Unit

3. R 7.8 mm
R 6.5 mm
0.5mm
0.67mm
+48 D
-5D
Net +43 D
n=1.336
n=1.336
n=1.386
n=1.406

4. Surface ectoderm
NCC

5. Epithelium
Superficial 2 layers of flattened cells
2-3 layers of wing or umbrella cells
Basal layer of columnar cells

6. Flattened cell layer
cell adhesions – Ds, MO, ZO
0.5 mm
height

7. Wing shaped cells
• 2 -3 layer
• Polyhedral shaped cells

8. Basal cell layer
Mitosis
Transparency & barrier function
Pentose pathway >> aerobic oxidation
0.05 um thick
Formed of collegan IV & laminin
Epithelial cell adhesion
Ds
MO
Hemidesmosomes

9. 1. Not a true membrane but rather the acellular condensate of the most anterior
portion of the stroma.
2.Provided resistance to infection & injury.
3.When disrupted, it will not regenerate and can form a scar

10. Others cells r-
Wondering Microphages
Histiocytes
Lymphocytes

11. • Descemet’s Membrane ( Basemant Membrane Of The Endothelium)
• Very resistant to injury or infection
• Can regenerate
• Elastic without elastic fibers
• Made of collegen & glycoproteins
• Thickness varies with age ( at birth – 3mm, adult – 10-12 mm)

12. Descemet’s Membrane
• The anterior “banded” region (A)
is secreted by the endothelial
cells during fetal development
and ismore highly organized
than
• The posterior “amorphous
region” (P), which is secreted
after birth.

14. Endothelium

16. Blood Supply
• Avascular cornea receive nourishment by small loops derived from
Anterior Ciliary Vessels

18. • The LPCN enters the eye along with SPCN around the optic N & runs
forwards in supracoroidal space.
• A short distance from the limbus they leave the sclera and divides
dichotomously & connect with the conjunctival N to from pericorneal
plexus of N.
• From this plexus 80-90 mylinated nerve fibres enter the cornea ,looses
their mylien sheet and from stromal plexus.
• Most of them passes anteriorly & from subepithelial plexus.
• From here they penetrates bowmen’s mem., lose there schwann’s sheath
&from intra epithelial plexus.

19. Transparency Of Cornea

20. CORNEAL
EPITHELIUM
&
TEAR FILM
• ARRANGMENT
OF STROMAL
LAMELLAE
CORNEAL
VASULARIZATION
• CORNEAL
HYDRATION
CELLULAR
FACTORS

21. Corneal Epithelium
• Transparent due to homogenicity of its refractive index & a
normal PRECORNEAL TEAR FLIM .
• Basal cells are firmly joined laterally to other basal cells and
anteriorly to the wing cells by desmosomes and macule
occludentes.
• Thse tight intercellular junction accounts for corneal
transparency.
• As well as it resistance to flow of water, electrolytes and
glucose(BARRIER FUNCTION).

22. ARRANGEMENT OF STROMAL
LAMELLAE
1. Maurice theory.
2. Theory of Goldman et al.

23. Maurice theory
• Cornea is transparent becoz fibrils are regularly arranged in a lattice,
& seperated by less than a wavelength of light (4000-7000A) due to
which scattered light is destroyed by the mutual interference.
 point against it– absence of lattics arrangement on electron
microscopy

24. • cornea is transparent because the fibrils are small in relationship to the
light and do not interfere with light transmission unless they are larger
than one half a wavelength of light (2000 A).
• Point that favours it is the presence of “Lakes”
areas devoid of collagen, found in non transparent corneas (>2K A)
Theory of goldman et al

25. CORNEAL VASCULARIZATION
• Cornea is transparent becoz it is avascular.
• Progressive vascularization, is a harmful process as it interfere
with functional properties of cornea, especially its
transparency.

26. • Cornea maintains it self in state of relative dehydration.
• Highest water content (80%) of any connective tissue in body.
• It is kept constant by balance of factors
• Which draw water in the cornea (SP, IOP)
• Which prevent the flow of water in the cornea ( Mech. Barrier)
• Which draw water out of the cornea (Pumps)
CORNEAL HYDRATION

27. • 1) Stromal swelling Pressure (SP) = 60mm Hg
 pressure exerted by GAG in the corneal stroma which
acts like a sponge. (SP)
 The electrostatic repulsion of the anionic charges on the
GAG Molecules expand the tissue ,sucking in the fluid -
with equal negative pressure= Imbibition Pressure (IP)
 In vitro- IP=SP
 In vivo- IP= IOP-SP i.e 17-60= -43mmHg

28. • 2) Barrier function of epithelium& endothelium
• The epithelium and endothelium acts like a semipermeable
membrane
• The epithelium offers twice the resistance to flow of water & act
as a perfect semipermeacble membrane for Small solutes –urea
and sod.chloride.
• In endothelium these solutes diffuse across the layer while
water is extracted osmotically.
• Barrier function of endothelium is Calcium dependant.

29. • 3) IOP
IOP > SP= corneal edema
4) Evaporation of water from corneal surface
Have little effect
The Evaporation of water from precorneal tear film
would concentrate this fluid and increase its
osmolarity relative to the cornea.
The hypertonicity of the tear film would draw water
from the cornea. This loss of fluid is however replaced
by the aqueous.

30. • 5)active Pump Mechanisms
<A> Na/K Atpase Pump System:
More Active In The Endothelium Than In The Epithelium.
There Is Active Extrusion Of Na From The Tissue.
Oubain, (Atpase Inhibitor) When Applied To The Eye Blocks Endothelial Fluid Transport Resulting In Corneal Overhydration.
<B> Hco3 Dependent Atpase:
This Enzyme Is Present In The Mitochondria
. Depletion Of Hco3 From Incubation/Perfusion Medium Induces Swelling.
Inhibitor- Thiocyanate
<C> Carbonic Anhydrase Enzyme:
Present On The Endothelium.
Moves Fluid From Stroma To Aqueous Humour.
<D> Na/H Pump:
Present In Lateral Plasma Membrane Surface.
<E> Passive Ion Movement:
K+, Cl-, Hco3- --- Diffuse Into Aqueous
Na+, Cl- , Hco3- ------ Diffuse From Aquous To Cornea.

31. CELLULAR FACTORS
Keratocytes (corneal fibroblasts)-
Enzymes required for the matrix assembly are encoded in the
genes of keratocytes
Any defect in the gene causes corneal opacification-
mucopolysaccharidoses.