The cornea consists of 5 layers: 1. Epithelium - acts as a barrier and is regenerated every 7 days through cell migration. 2. Bowman's layer - acellular layer that provides strength. 3. Stroma - thick collagenous layer that gives the cornea its strength and transparency. 4. Descemet's membrane - basement membrane secreted by the endothelium that increases in thickness with age. 5. Endothelium - single cell layer that regulates hydration of the stroma and maintains corneal transparency.

2.  The cornea is a
transparent,
nonvascular tissue
which forms the
anterior surface of
the eye.

3.  Light enters the eye
through the major
refractive structure
of the eye,
focusing light onto
the retina
 The cornea
protects the fragile
intraocular
contents by its
tough, yet pliable
collagen structure.

4.  Horizontally 11 – 12 mm
 Vertically 10 – 11 mm
 Radius of curvature 7.8mm
(6.7 - 9.4 )
 Power 43.25 D

5.  It helps to shield the rest of the eye from
germs, dust, and other harmful matter. The
cornea shares this protective task with the
eyelids, the eye socket, tears, and the sclera.
The cornea acts as the eye’s outermost
lens.

6.  Epithelium
 Bowman’s Layer
 Stroma
 Decrement's
membrane
 Endothelium

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

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

9. There’s no cell
devision.
Polygonal cells:
• Small light cells
(young cells)
reached the surface of the
cornea
• Dark cells (mature
cells)
will be sloughed

10. The surface cells are
covered with a dense
coat of microplicae, and
dark cells have fewer
microplicae than do
light cells. The darker
cells have fewer
microvilli and
microplicae near the cell
margins. Adhering to
this microvilli is a
glycocalyx.

11. Apical membrane of the
surface epithelium and
intercellular junctions along
the lateral membranes.
Glycocalyx emerging from
the surface microvilli.A tight
junction and densely
staining desmosomes are
seen along the lateral
membranes. Glycogen is
evident as well as
numerous vesicles point to
microvilli from two adjacent
surface cells.

12. There’s no cell division.
A prominent
characteristic of these
cells is an
abundance of
intracellular keratin
tonofilaments. Wing
cells are distinguished
by a variety of
polygonal shapes and
by their large ovoid
nuclei.

13. The corneal
epithelium is refered to
as a nonkeratinized
epithelium because it
normally does not
express the cornified
cytoskeleton typical of
epidermal cells.
The situation changes
in Vit A deficiency when
the corneal epithelium
express keratins
normally found in the
cornified epithelium, or
epidermis, of the skin.

14. A single layer of cuboidal cells
Originate from the stem cells in the
basal layer of the limbal epithelium,
which is peripheral to the cornea. They
also contain glycogen.
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

15. Basement membrane is secreted extracellularly by the epithelial cells and forms
one of several structural components associated with cell adhesion to Bawman’s
Layer or stroma. Made up primarily of type IV, VII, XII collagen, laminin,
Fibronectin and heparan sulfat proteoglycan.
• Lamina Lucida (anteriorly, 23nm)
• Lamina densa (apposed to Bawmen’s layer)
• Reticular lamina (within to Bawmen’s layer)

16. Basal cells and entire
epithelium adhere to the
basement membrane and
stroma via hemidesmosomes
(integral plazma membrane
protein)
The basal,wing, and
superficial cells are linked to
one another by desmosomes,
which are more numerous
among superficial cells than
between basal cells.

17. Bullos pemfigoid
antigen
&
Integrin
heterodimer
Intracellular domains
linked
Keratin filaments
L.R
In the basement
membrane linked Anchoring fibrils (VII collagen)
Pass through B.L. into
The stroma, penetrates
Anchoring plaques (which composed laminin)
Cell adhesion complex
 L.R.- laminin receptor
 B.L.- Bawman’s layer

18. Junctional complexes of the cornea
Gap junction Tight junction
More numerous in the more basal
Layers than in the superficial cells.
This junction is between basal and
wing cells
Gap junction forms a functional
Syncytium, which may be important
In coordinating functions such as
cell differentiation and migration.
Only between superficial cells!!!!
Tight junction or zonula occludens
(ZO), which form a highly effective
Semipermeable membrane on the
surface of the cornea.
Tight junction is important to the
barrier function.

19. Y YX
X + Y = Z
Z
X - proliferation of
basal cells
Y - centripetal movement of
cells
Z - cell loss from the surface.
X, Y, Z Hypothesis of corneal
epithelial maintenance.

20. II. Bowman’s layer
Bowman' s layer appears as a
feltlike, composite of randomly
oriented, striated collagen fibrils
dispersed throughout an amorphous
matrix . In the adult this layer is
approximately 8 to 12μm thick,
being slightly thicker in the corneal
periphery. Bowman's layer is
acellular, except for nerve axons
coursing toward the epithelium. The
lack of keratocyte (fibroblast) cells
within Bowman's layer may indicate
its inability to regenerate after injury,
or it may imply that keratocytes
cannot migrate into Bowman's layer.

21. III. Stroma
Stroma, a fibrous tissue layer
approximately 450μm thick in the
central cornea. There are type I
collagen with types III, V, and VI.
The stroma is a predominantly an
ECM comprised of a lamellar
arrrangement of collagen fibrils
running parallel to the corneal
surface, with the individual
collagen fibrils separated by a
matrix of proteoglycans. The
collagen fibrils and ECM are
maintained by cells called
keratocytes . That lie between the
collagen lamellas.

22. Central cornea
Central
cornea
Peripheral cornea
Annulus of collagen fibers
1.5-2.0 mm wide around
the cornea
 The collagen fibers
refractive index is 1.4

23. The extrafibrillar material sometimes called the Ground
Substance of the stroma, is largely made up of
proteoglycans
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.
 lumican
 keratocan
 mimecan
All in
keratotocytes
synthesize
collagen.
 CD/DS - chondroitin sulfat/dermatan sulfat
 KS - keratan sulfat

24.  Lumican,keratocan, and mimecan are also found
in other tissues. Only in the cornea they are
present in a highly sulfated form.
This sulfation of the cornea chains increases the
wateretentive properties of the proteoglycans,
which affects hydration of the stroma and hence
corneal transparency

25. IV. Descemet’s layer
The cornel endothelium rests on a
basement membrane, known as a
descemet’s membrane, which in the
adult eye 10-15 micron thick. This
membrane is secreted by endothelial
cells and increases in thickness
throughout life.

26. The basement membrane components :
 Type IV collagen
 Laminin
 Fibronectin (functions in adhesion
endothelial cells to the
membrane)
Descemet’s membrane may remain intact in
cases of severe corneal ulceration, forming
a descemetocele after destruction of the
epithelium and stroma.
this shows that the membrane is highly
resistant to proteolytic enzymes.

27. V. Endothelium
Single layer of cells covers the
posterior surface of the cornea .
Polygonal cells most of which are
hexagonal (d- 20µm, thick – 4-6µm)
Newborns – 5500 cells/mm2
Adults -- 2500-3000 cells/mm2
Min level -- 400-700 cells/mm2

28. Endothelial cells are
interconnected by tight and
gap junction . The endothelium
forming a “leaky” barrier
between the aqueous humor &
the stroma (by tight junction).
The gap junction do not
contribute to the endothelial
barrier, but the funtion in
intercellular communication

29. Polymegathizm – the abnormal size of the
endothelial cells.
 Polymorphizm – a decrease in hexagons with a
concomitant increase in number of
cells
Polymegatizm and pleomorphizm
are increasing with aging.

30. Cornea’s innervation.
nerves In the middle third
of the stroma
cornea
anteriorly
forward
radially
Toward the central
area
Giving branch and
innervate
Anterior stroma
Plexus subepithelial
Bowman’s layer
Subbasal
epithelial
nerve plexus
Basal epithelial cell layer
And terminating
Superficial epithelial layers.

32. Nutrition of the cornea
 Aqueous Humour
 Perilimbal vessels

33. And in the end the funny cornea’s pictures
for you!!!

34. I hope it was interesting,
Thank you
for your attention.