The eye is an important organ of
sight of the body having a very complicated
structure. This organ functions best,
when all the parts of its structure
are working well.
The eye is shaped like a ball which
is moved by muscles attached to it.
It has a tough, outer, white coating,
called the sclera, which covers the
whole eye, except the cornea. Inside
the sclera are contained the essential
parts. These essential parts are the
Cornea: It is the transparent, dome-shaped,
front part of the eye. It is a powerful
refracting surface, providing most
of the eye’s optical power.
The cornea is unique among the eye
parts, as it has no blood vessels
and therefore can be transplanted.
The cornea has numerous nerve endings,
making it the most sensitive part
of the eye. The tear glands keep the
cornea moist and clean.
Pupil: In the centre of the cornea
is a black hole known as the pupil,
through which light enters. The pupil
controls the amount of light that
should be entering the eye. More or
less than the necessary amount of
light, may not produce the correct
Iris: It is the pigmented part, which
decides the color of your eyes. It
does not allow light to pass through.
It is the iris muscles, which changes
the size of the pupil
Lens: A little way inside the cornea
is the lens, which focuses the light.
Eye chambers: The lens divides the
eye into two unequal chambers called
the front or the anterior chamber
and the rear or the posterior chamber.
The smaller front chamber contains
a watery fluid, known as the aqueous
humor and the larger rear chamber
contains a jelly like substance called
the vitreous humor.
Choroid: The sclera is lined inside
by a pigmented membrane, the choroids.
Retina: The choroid in turn is lined
at the rear half of the eyeball by
the almost transparent parent retina.
The retina is to the eye what a film
is to a camera. The retina contains
millions of very sensitive photoreceptor
cells, called rods and cones that
are connected to the brain by optic
nerves. Rods and cones play a major
part in enabling you to see.
Additionally the eye is provided
with parts which protect it. Among
these are the eyelids and the eyelashes,
which function as barriers to the
entry of any foreign objects. The
eyelids have another important function
of spreading tears on the eye surface.
Tears are a salty fluid, produced
by lacrimal glands located under the
Secretions by some small glands and
parts and tears produce the tear film
which keeps the eye surface moist.
The tear film is important to keep
the cornea transparent and uninfected.
The eyes are kept clean by a continuous
supply of tears. Tears contain antibodies
which help prevent infection.
The entire eye is situated in a bony
structure, which protrudes beyond
the eye surface. This structure is
called the orbit. The orbit protects
the eye and at the same time allows
it to move freely.
Process of seeing
Light falling on the eye is allowed,
in the requisite mount, by the pupil
to enter it. The lens brings these
light rays to a focus on the retina
by using small eye muscles, known
as the ciliary body. These ciliary
muscles allow the lens to change its
shape so that the light is always
focused on the retina. The sensitive
rods and cones on the retina absorb
these light signals and convert them
into electrical impulses. The optic
nerves carry these electrical impulses
to the brain to produce the vision
that you see. The eye is always, adjusting
the amount of light to be let in,
focusing and instantly transmitting
signals to the brain.
The image on the retina is always
upside down, but it is the processing
done by the brain which makes us see
things right side up.
Because humans have two eyes, each
eye catches a different view of the
object being viewed. This is called
stereoscopic vision. The brain processes
signals received from both eyes to
produce a three dimensional vision
which has depth. This 3-D vision allows
us to judge distances and depth better.
Sight is our most important sense.
It is estimated that almost 80% of
our learning takes place through the
eyes. Eyes are therefore precious.
An understanding of how the eye works
and its importance will help you in
maintaining good eye health.