A view of the anatomy of Cornea.

1. PRESENTED BY - AL AMiN
B. OPTOMETRY 2nd YEAR.

2.  Word cornea has come from ‘Kerato’.
 Kerato in Greek mean ‘Horn’ or ‘Shield like’.
 Ancient Greek used to believe that cornea is derived from thin
sliced horn of animal.

3. ¤ The cornea is a transparent avascular tissue with a smooth ,
convex outer surface and concave inner surface with uniform
curvature , which resembles a small watch glass.
¤ The cornea is composed of proteins and cells.
¤ It does not contain blood vessels, unlike most of the tissues in
the human body. Blood vessels may cloud the cornea, which
may prevent it from refracting light properly and may
adversely affect vision.
¤ Since there are no nutrient-supplying blood vessels in the
cornea, tears and the aqueous humor (a watery fluid) in the
anterior chamber provide the cornea with nutrients.
¤ Light enters the eye through the major refractive structure of
the eye, focusing light onto the retina.

4. ¤ Anterior Surface :
- Elliptical , about 11.7mm horizontally and 10.6mm
vertically.
¤ Posterior Surface :
- Circular, about 11.7mm in diameter.
¤ Thickness :
- Centrally about 0.52mm.
- Peripherally about 0.67mm.
¤ Optical zone :
- Cornea is almost a sphere , the central 1/3rd is called optical
zone about 5.4mm.
¤ Radius of curvature :
- Anterior surface is about 7.8mm.
- Post. Surface is about 6.5mm.

6. ¤ Resistance provide protective layer.
¤ Resist ocular pressure due to collagenous
components of stroma.
¤ The cornea acts as the eye’s outermost lens. It
functions like a window that controls and focuses the
entry of light into the eye.

7. ¤ There are mainly 5 layers of cornea –
1. A nterior Epithelium.
2. B owman’s membrane.
3. C entral Stroma.
4. D ecemet’s membrane.
5. E ndothelium.
There is one more layer which comes between central
stroma and decement’s membrane –
6. Dua’s layer.

9.  50-90µ thick.
 Stratified squamous type.
 Tight junction in basal cells account for epithelium’s transparency.
 It acts as a barrier to protect the cornea , resisting the free flow of fluids
from the tears, and prevent bacteria from entering the epithelium and
corneal stroma.
 The corneal epithelium consists of several layers of cells.
 The cells of the deepest layer are columnar, known as basal cells which are
attached by multiprotein complexes known as hemidesmosomes to an
underlying basement membrane. Then follow two or three layers of
polyhedral cells, commonly known as wing cells. Lastly, there are three or
four layers of squamous cells, with flattened nuclei. The layers of the
epithelium are constantly undergoing mitosis. Basal and wing cells migrate
to the anterior of the cornea, while squamous cells age and slough off into
the tear film.
 Corneal epithelium sheds at regular interval. It takes normally about 7days
for replacement of entire corneal epithelium.

11.  The Bowman's membrane a smooth, acellular,
nonregenerating layer, located between the superficial
epithelium and the stroma in the cornea of the eye.
 It is composed of strong, uniformly oriented collagen fibrils
in which the smooth anterior surface faces the epithelial
basement membrane and the posterior surface merges with the
collagen lamellae of the corneal stroma proper.
 In adult humans, Bowman's membrane is 8-12 μm thick. With
ageing, this layer becomes thinner.

12.  The corneal stroma is a mesenchymal connective tissue
making up 90% of the corneal thickness, with physical
properties that provide the cornea its essential character.
 The stroma is formed during late embryogenesis by a
population of neural crest cells migrating from the
periocular mesenchyme.
 They are each about 1.5-2.5 μm in thickness.
 At its centre, human corneal stroma is composed of about
200 flattened lamellæ (layers of collagen fibrils),
superimposed one on another.

13.  Dua’s layer is a layer of the cornea that had not been detected
previously.
 The fourth caudal layer, and located between the corneal
stroma and Descemet's membrane.
 Despite its thinness, the layer is very strong and impervious to
air.
 Dua’s layer is well-defined, acellular and strong, consisting of
five to eight lamellae of type-1 collagen bundles totalling
about six to 15 microns thickness.
 The bundles are coarse and arranged in transverse,
longitudinal and oblique directions.
 Bundle spacing is similar to that in stromal tissue, but Dua’s
layer is entirely free of keratocytes in the zone that forms the
posterior wall of the bubble.

14.  Descemet's membrane is the basement membrane that lies
between the corneal proper substance, also called stroma,
and the endothelial layer of the cornea.
 It is composed of different kinds of collagen (Type IV
and VIII) than the stroma.
 The endothelial layer is located at the posterior of the
cornea.
 Descemet's membrane, as the basement membrane for
the endothelial layer, is secreted by the single layer of
squamous epithelial cells that compose the endothelial
layer of the cornea.
 Its thickness ranges from 3 μm at birth to 8–10 μm in
adults.

15.  The corneal endothelium is a single layer of endothelial cells
on the inner surface of the cornea.
 It faces the chamber formed between the cornea and the iris.
 The corneal endothelium are specialized, flattened,
mitochondria-rich cells that line the posterior surface of the
cornea and face the anterior chamber of the eye.
 The corneal endothelium governs fluid and solute transport
across the posterior surface of the cornea and maintains the
cornea in the slightly dehydrated state that is required for
optical transparency.
 The number of endothelial cells in the fully developed cornea
decreases with age up until early adulthood, stabilizing around
50 years of age.
 The corneal endothelium is attached to the rest of the cornea
through Descemet's membrane, which is an acellular layer
composed mostly of collagen IV.

16. ¤ Cornea is an avascular structure.
¤ Small loops derived from the anterior ciliary vessels invade its
periphery for about 1mm and provide nourishment.
¤ These loops are not in cornea but in the subconjunctival tissue
which overlaps the cornea .

17. ¤ The cornea is one of the most sensitive tissues of the body and
has one of the richest sensory nerve supplies in the body.
¤ It is supplied by long and short cilliry nerves from the
ophthalmic division of the trigeminal nerve.

18. At limbus,
¤ Corneal epithelium becomes bulbar conjunctival epithelium.
¤ Bowman’s membrane becomes continuous with the lamina
propria of the conjunctiva and tenon’s capsule.
¤ Stroma becomes sclera.
¤ Decements membrane becomes schwalbe’s line.
¤ Endothelium lines the trabecular meshwork and becomes
continuous with the anterior surface of the epithelium.

19. ¤ Tight junctions of the epithelial cells .
¤ Endothelial pump mechanism.
¤ Absence of blood vessels.
¤ Absence of pigments.
¤ Scarcity of cell nuclei in stroma.
¤ Uniform structure of stroma.

20. ¤ The cornea, with the anterior chamber and lens, refracts
light.The cornea accounting for approximately two-thirds of
the eye's total optical power. In humans, the refractive power
of the cornea is approximately +43 dioptres. ... While the
cornea contributes most of the eye's focusing power, its focus
is fixed.