Basic Parts of the human eye.

2. The human eye is a complex part of the body that is
used for seeing. Eyes enable people to perform daily
tasks and to learn about the world that surrounds
them. Sight, or vision, is a rapidly occurring process
that involves continuous interaction between the eye,
the nervous system, and the brain. When someone
looks at an object, what he really sees is the light
reflected from the object. This reflected light passes
through the lens and falls on the retina of the eye. Here
the light induces nerve impulses that travel through the
optic nerve to the brain and then over other nerves to
muscles and glands.

3.  The eye is similar to a television
camera. Both the eye and the
television camera converts light
energy to electrical energy. The
eye converts light to nerve
impulses that are interpreted by
the brain as the sense perception
called sight. A television camera
converts light to electronic
signals that are broadcast and
transformed into light images in
a television receiver.

4. The eye is well protected. It lies within a bony socket
of the skull. The eyelids guard it in front. They blink
an average of once every six seconds. This washes
the eye with the salty secretion from the tear
glands. Each tear gland is about the size and shape
of an almond. These glands are situated behind the
upper eyelid at the outer corner of the eye. After
passing over the eye, the liquid from the gland is
drained into the nose through the tear duct at the
inner corner of the eye.

5. Structure
• The eye is shaped like a ball,
with a slight bulge at the
front. It is this bulge that a
person sees when looking
at the eyes of someone
else. When the eyelids are
closed, the bulge is
covered. The rest of the eye
is protected by the bones of
the skull. Each part of the
human eye has a special
function.

7. Hearty laughter or weeping causes muscles in
the upper eyelid to squeeze the lachrymal gland.
This produces tears that flow too fast to be
drained away. The eyelashes catch many flying
particles that otherwise would enter the eye. As
a further protection, the eyelids automatically
close when any object suddenly moves close to
the eye.

9. Cornea and sclera.
 The eye is made of three coats, or
tunics. The outermost coat consists
of the cornea and the sclera; the
middle coat contains the main
blood supply to the eye and
consists of the choroid, the ciliary
body, and the iris. The innermost
layer is the retina. The sclera, or the
white of the eye, is composed of
tough fibrous tissue. On the
exposed area of the eye the sclera
surface is covered with a mucous
membrane called the conjunctiva.
This protects the eye from
becoming dry. The cornea, a part of
the sclera, is the transparent
window of the eye through which
light passes. The focusing of light
begins in the cornea.

10. • Behind the cornea is a
watery fluid called the
aqueous humor. This fluid
fills a curved, crescent-shaped
space, thick in the
center and thinner toward
the edges. The cornea and
the aqueous humor
together make an outer
lens that refracts, or
bends, light and directs it
toward the center of the
eye.
Aqueous humor

11. Iris.
Behind the aqueous humor is a colored ring
called the iris. The color of the iris is inherited
and does not affect vision. The iris is like a
muscular curtain that opens and closes. It
controls the amount of light entering the eye
through the pupil, an opening in the iris. The
pupil looks like a black spot. Light from
everything a person sees must go through the
pupil. When more or less light is needed to see
better, the pupil becomes larger or smaller
through the movement of the muscle in the iris.
The aqueous humor flows through the pupil into
a small space between the iris and the lens.

12. The pupil is the hole
in the center of the
iris that light
passes through.
The iris muscles
control its size.

13. • A simple way to see how the pupils respond to
light is to stand in front of a mirror with the
eyes closed, covered by the hands for about
ten seconds. When the hands are removed
and the eyes opened, the pupils begin to get
smaller, or contract, in response to the light.
When light is reduced, pupils expand; when it
is increased, they contract

14. Choroid
• The choroid is a layer of
blood vessels and
connective tissue
squeezed between the
sclera and the retina. It
supplies nutrients to the
eye. The ciliary body is a
muscular structure that
changes the shape of the
lens.

15. • The eye's crystalline lens
works like the adjustable
lens in a camera.
Positioned just behind the
cornea; it is responsible for
keeping images in focus on
the retina. It is adjustable
for distance and close
work.

16. Cataract
• A cataract is the lens
clouding up. This happens
to most people as they age.
A few people are even born
with cataracts. Modern
surgery has all but
eliminated cataracts as a
cause of blindness in the
developed world.

17. Retina.
The retina is a soft,
transparent layer of
nervous tissue made up of
millions of light receptors.
The retina is connected to
the brain by the optic
nerve. All of the structures
needed to focus light onto
the retina and to nourish it
are housed in the eye,
which is primarily a
supporting shell for the
retina.

18. Macula - (yellow spot)
• This part of the retina is the
most sensitive. Its diameter
is only 7 mm or about 1/4
inch. It is responsible for our
central, or reading vision.
This part of the retina gives
us 20/20 vision. Without the
macula, you would be blind
- Legally Blind that is. People
with eye diseases like
Macular Degeneration have
vision from 20/200 to
20/800.

19. Vitreous Humor
• The vitreous humor is a jelly like
liquid that fills most of the eye
(from the lens back). As we age
it changes from a gel to a liquid
and gradually shrinks separating
from the retina. This is when
people start seeing floaters,
dark specs in their vision. This is
a normal sign of aging, but in a
few cases the retina can
become detached as the
vitreous separates

20. Optic Disk
• The optic disk is the spot on the
retina where the optic nerve leaves
the eye. There are no sensory cells
here, creating a blind spot. Each eye
covers for the blind spot of the
other eye and the brain fills in the
missing information.
Optic disk

21. Optic Nerve
• Each optic nerve has
about 1.2 million nerve
fibers. This is the cable
connecting the eye to the
brain.

23. By SHAHANA