The cornea is the transparent circular
part of the front of the human eyeball.
It has an important optical function as it refracts light entering the
eye through the pupil
and onto the lens
(which then focuses the light onto the retina).
The degree of curvature of the cornea varies between individuals and
also throughout the life of an individual. It is more prominent in youth
than later in life, when it can become flatter in shape.
The cornea has a complex structure that specialist texts
describe in terms of the following layers (from the outside inwards) :
_1. _ Several
strata of epithelial cells, continuous with those of the conjunctiva ;
_2. _ A thick
central fibrous structure called the substantia propria ;
_3. _ A homogeneous
elastic lamina ;
_4. _ A single
layer of endothelial cells forming part of the lining membrane of the
anterior chamber of the eyeball.
The cornea a non-vascular structure (which means that it does not contain
any blood vessels) as the capillaries
that supply it with nutrients terminate in loops at its circumerfence.
It is supplied by many nerves derived from the ciliary nerves. These enter
the laminated tissue of the cornea. It is therefore extemely sensitive.