The cornea is a transparent, avascular tissue which forms the anterior surface of the eye.

2. The cornea isa
transparent,
avascular tissue
which forms the
anterior surface of
the eye.

3. Light enters theeye
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. Measures of the cornea:
• The anterior surface of the cornea is elliptical with an
average horizontal diameter of 11.7 mm and vertical diameter
of 11 mm.
• The posterior surface of the cornea is circular with an
average diameter of 11.5mm.
• Thickness of cornea in the center is about 0.52mm while at
the periphery it is 0.7 mm.
• Radius of curvature. The central 5 mm area of the cornea
forms the powerful refracting surface of the eye. The anterior
and posterior radii of curvature of this central part of the
cornea are 7.8 mm and 6.5 mm, respectively.

5. Refractive power of the cornea
is about 45 dioptres, which is
roughly three-fourth of the
The total refractive power of the
eye (60 dioptres).

6. Epithelium
Bowman’s Layer
Stroma
Descemet's
membrane
Endothelium

7. 1. Epithelium. It is of stratified squamous type and becomes continuous with the
epithelium of bulbar conjunctiva at the limbus. It consists of 5-6 layers ofcells. The
deepest (basal) layer is made up of columnar cells, next 2-3 layers of wing or umbrella
cells and the most superficial two layers are of flattened cells.
2. Bowman's membrane. This layer consists of acellular mass of condensed collagen
fibrils. It is about 12μm in thickness and binds the corneal stroma anteriorly with the
basement membrane of the epithelium.It is not a true elastic membrane but simply a
condensed superficial part of the stroma. It shows considerable resistance to infection.
But once destroyed, it does not regenerate.

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

9. 3. Stroma (substantia propria). This layer is about 0.5 mm in
thickness and constitutes most of the cornea (90% of total
thickness). It consists of collagen fibrils (lamellae) embedded in
hydrated matrix of proteoglycans. The lamellae are arranged in
many layers. In each layer they are not only parallel to each
other but also to the corneal plane and become continuous with
scleral lamellae at the limbus. The alternating layers of lamellae
are at right angle to each other. Among the lamellae are present
keratocytes, wandering macrophages, histiocytes and a few
leucocytes.

10. 4. Descemet's membrane (posterior elastic lamina).
The Descemet's membrane is a strong homogenous layer which bounds the stroma
posteriorly. It is very resistant to chemical agents, trauma and pathological processes.
Therefore, 'Descemetocele' can maintain the integrity of eyeball for long. Descemet's
membrane consists of collagen and glycoproteins. Unlike Bowman's membrane it can
regenerate. Normally it remains in a state of tension and when torn it curls inwards on
itself. In the periphery it appears to end at the anterior limit of trabecular meshwork as
Schwalbe's line (ring).
5. Endothelium. It consists of a single layer of flat polygonal (mainly hexagonal) cells
which on slit lamp biomicroscopy appear as a mosaic. The cell density of endothelium is
around 3000 cells/mm2 in young adults, which decreases with the advancing age. There
is a considerable functional reserve for the endothelium. Therefore, corneal
decompensation occurs only after more than 75 percent of the cells are lost. The
endothelial cells contain 'active-pump’ mechanism.

12. Blood supply
Cornea is an avascular structure. Small loops derived from the anterior ciliary vessels
invade its periphery for about 1 mm. Actually these loops are not in the cornea but in
the subconjunctival tissue which overlaps the cornea.
Nerve supply
Cornea is supplied by anterior ciliary nerves which are branches of ophthalmic division
of the 5th cranial nerve. After going about 2 mm in cornea the nerves lose their myelin
sheath and divide dichotomously and form three plexuses — the stromal, subepithelial
and intraepithelial.

13. Thank you