The cornea is the transparent front part of the eye that refracts light. It is avascular and has five layers - epithelium, Bowman's layer, stroma, Descemet's membrane, and endothelium. The stroma makes up most of the thickness and contains collagen bundles and proteoglycans. The cornea is nourished by the aqueous humor and innervated by nerves from the trigeminal nerve. It serves to transmit and refract light entering the eye, as well as protect the inner structures.

1. CORNEA
Shahana
Nethradhama school of optometry

2. The cornea is a transparent avascular tissue with
a smooth convex outer surface and concave
inner surface,which resembles a small watch
glass.
To meet the diverse functional demands the
cornea must be:
Transparent
Refract light
Contain the intraocular pressure
Provide a protective interface

3. DIMENSIONS
Anterior surface:
• Ellipitical,about 11.7mm horizontal and 10.6
mm vertically
Posterior surface:
• Circular , about 11.7 mm in diameter

4. Thickness:
• Centrally about 0.52mm
• Peripherally about 0.67mm
Surface area:
• About 1.3cm²
Optical zone:
• Cornea is almost a sphere,the central 1/3rd is called
optical zone about 5.4mm
Radius of curvature:
• Anterior surface – about 7.8mm
• Posterior surface – about 6.5mm
Refractive power:+43.1 D
Refractive index:1.376

6. COMPOSITION OF HUMAN CORNEA
Water :78%
Collagen:15%
Other proteins: 5%
GAGs:1%

7. STRUCTURE
Behind the precorneal tear film there are five
layers of cornea:
i. Epithelium
ii. Bowman’s layer
iii. Stroma
iv. Decement membrane
v. Endothelium

8. Epithelium:
The corneal epithelium is :
• Stratified,squamous and non keratinised
• Continuous with conjuctival epithelium at limbus
but having no goblet cells
• 50micron thick
• Consists of 5 or 6 layers of nucleated cells
resting on a basal lamina , namely
a) Basal cells
b) Wing cells
c) Surface cells

9. Bowman’s layer
• Modified region of anterior stroma
• Acellular homogeneous zone
• 8-14 micrometer thick
• Anterior surface is smooth and parallel with
corneal surface

10. Stroma: (substantia propria)
• About 500 micrometer thick
• Consists of regularly arranged lamellae of collagen
bundles,lie in proteoglycan ground substance with-
 200-300 bundles-centrally
 500 bundles-peripherally
 Width about 9 – 260 micrometer
 Height about 1.15-2micrometer
• small population of cells- keratocytes present.
• Keratocytes occupy 2.5 – 5 % of total stromal volume
and is responsible for synthesis and maintaining of
collagen and proteoglycan substance of stroma.

11. Arrangement of lamellae-
• Lamellae are arranged in layers and are
parallel with each other and with corneal
surface
• In deeper the stroma the lamellae form strap
like ribbons which run approximately at right
angles to those in consecutive layers
• At the limbus the bundles appeared to take a
circular course

12. Descemet’s membrane:
• It is the basal lamina of corneal endothelium
• First appears at 2nd month of gestation and
synthesis continue through out adult life
• About 10 micrometer thickness

13. Endothelium:
• It is a single layer of hexagonal,cuboidal cells attached
posterior ascept of decement membrane
• It is nuroectoderm in origin
• The endothelium can be viewed by specular reflection
using a slit-lamp biomicroscope at high magnification (25X -
40X)
• Corneal endothelium cells production is relatively fixed and
it is about 500,000
• At birth cells are 10 micrometer in height with age it
becomes flattened to 3-5 micrometer and 18-20
micrometer width
• Endothelium gets its nutrition and oxygen from aqueous

14. Blood supply of cornea
• The cornea is avascular structure
• Small loop derived from the anterior ciliary
vessels invade its periphery for about 1mm
and this loops are in the subconjunctival tissue
which overlaps the cornea.

15. Nerve supply of cornea
• Cornea is rich in sensory nerve supply derived
from ophthalmic division of trigeminal nerve
via anterior ciliary nerves and nerves to the
surrounding conjunctiva
• The nerve fibres become more visible when
the cornea is oedematous