Anatomy of the Cornea Part and functions

1. GROUP II
BEVERLINE KHAVERE
LORNA JEPTUM
JOY MIRACLE
MARION KEMBOI
WYCLIFFE JUMA
GEORGE OKELLO

2. THE
CORNEA

3. THE STRUCTURE
 A transparent ,dome-shaped structure at the front of the
eye
 More convex than the sclera but curvature diminishes with
age
 It is avascular and highly innervated
 It accounts for approx. two thirds of the eyes total optical
power i.e. 43 diopters
 It covers the iris and the pupil
 The cornea has unmyelinated nerve endings sensitive to
touch, temperature and chemicals
 Oxygen dissolves in tears then diffuses throughout the
cornea to keep it healthy

4. CONT.
 Nutrients are transported via diffusion from the tear fluid
through the outside surface and the aqueous humor
through the inside surface and also from neurotrophins
supplied by nerve fibres
 It has a diameter of about 11.5mm and a thickness of 0.5-
0.6mm in the centre and 0’.6-0.8mm at the periphery
 Transparency,avascularity,the presence of immature
resident immune cells and immunologic privilege makes it
a very special tissue
 Human cornea borders with the sclera via the corneal
limbus

5. LAYERS OF THE CORNEA
 Corneal epithelium
 Bowman’s layer
 Corneal stroma
 Descemet’s membrane
 Corneal endothelium

7. CORNEAL EPITHELIUM
 Exceedingly thin multicellular epithelial tissue
layer(non-keratinized stratified squamous epithelium)
of fast growing and easily regenerated cells, kept moist
with tears
 Continuous with the conjunctival epithelium and is
composed of about 6 layers of cells which are shed
constantly on the exposed layer and are regenerated by
multiplication in the basal layer

8. BOWMAN’S LAYER
 A tough layer composed of collagen(mainly type I
collagen fibrils),laminin,nidogen,perlecan that
protects the corneal stroma

9. CORNEAL STROMA
 Also called subtantia proper
 A thick ,transparent middle layer consisting of
regularly arranged collagen fibres along with
keratocytes-cells for general repair and maintenance
 They are parallel and superimposed like book pages
 The corneal stroma consists of approx. 200 layers of
main type I collagen fibrils
 Each layer is 1.5-2.5µm
 Up to 90% of the corneal thickness is composed of
stroma

10. Theories of the corneal
transparency
1. The lattice arrangements of the collagen fibril in the
stroma .The light scatter by individual fibrils is
cancelled by destructive interference from the
scattered light from the other individual fibrils
2. The spacing of the neighboring collagen fibrils in the
stroma must be less than 200 nm for there to be
transparency

11. DESCEMET’S MEMBRANE
 A thin acellular layer that serves as the modified
basement membrane of the corneal endothelium
 Composed mainly of collagen type IV fibrils less than
collagen type I fibrils
 Around 5-20 µm thick depending on age
 Anterior to Descemet’s membrane, is a very thin and
strong layer,Dua’s layer,15 microns thick and is able to
withstand 1.5-2 bars of pressure

12. CORNEAL ENDOTHELIUM
 A simple squamous or low cuboidal monolayer
approx.5µm thick, mitochondria-rich cells which
regulate fluid and solid transport to the aqueous and
corneal stroma compartments
 Corneal epithelium do not regenerate- The stretch to
compensate for dead cells reduces the overall cell
density which affects fluid regulation
 This leads to stromal swelling due to excess fluids and
subsequent loss of transparency which in turn causes
corneal edema and interference of the cornea and thus
impairing the image formed.

13. NERVE SUPPLY
 It is one of the most sensitive tissues in the body
 It is densely innervated with sensory nerve fibres via
the ophthalmic division of trigeminal nerve by way of
70-80 long cilliary nerves
 Ciliary nerves run under the endothelium and exit the
eye through the sclera apart from the optic nerve
 The nerves enter the cornea via 3 levels;
Scleral
Episcleral
Conjunctival

14. CONT.
 Most of the bundles give rise by subdivision to a network in
the stroma from which fibres supply the different regions
 The 3 networks are;
I. Midstromal
II. Sub epithelial/sub-basal
III. Epithelial
 Corneal nerves of the sub epithelial layer terminate near
the superficial epithelial layer of the cornea in a
logarithmic spiral pattern
 The density of epithelial nerves decrease with age
especially after the seventh decades

15. FUNCTIONS OF THE CORNEA
 It helps focus and direct light onto the retina
 It acts as a thick elastic physical barrier protecting the
internal ocular structure from outside insults which
may be physical ,chemical and microbial
 It withstands changes in intraocular pressure and
curvature changes of the eye