THE

THEHUMAN
HUMANEYE
EYEAND
ANDTHE
THE
COLOURFUL
COLOURFULWORLD
WORLD
Name: Dhananjay
Class- Xth
Roll No- 22
School- Kendriya Vidyalaya
Bhavnagar

The Human

INTRODUCTION
The human eye is the organ which
gives us the sense of sight,
allowing us to observe and learn
more about the surrounding world
than we do with any of the other
four senses. We use our eyes in
almost every activity we perform,
whether reading, working,
watching television, writing a

Most people probably would

agree that sight is the sense
they value more than all the
rest.
The eye allows us to see and
interpret the shapes, colors,
and dimensions of objects in
the world by processing the
light they reflect or emit. The
eye is able to detect bright

PARTS OF THE HUMAN EYE

CORNEA
The cornea is a clear, dome-shaped
surface that covers the front of the
eye. Tears that flow over it and
aqueous humor in the chamber behind
it keep it nourished. It allows the light
to enter the eyeball. The eyeball is
approximately spherical in shape with
a diameter of about 2.3 cm. When you
hear of eye banks and eye transplants,
it is the cornea that is being replaced.
The cornea can be damaged from:

IRIS
This is the colored part of the eye:
brown, green, blue, etc. It is a ring
of muscle fibers located behind
the cornea and in front of the lens.
It contracts and expands, opening
and closing the pupil, in response
to the brightness of surrounding
light. Just as the aperture in a
camera protects the film from over

PUPIL
The pupil is the hole in the
center of the iris that light
passes through. The iris
muscles control its size. It
contracts in excess light and
expands in dimlight.

Ciliary Muscle
The eye can bring the fine print in a
phone book into focus, or focus in on
the moon over million miles away.
The ciliary muscle changes the shape
of the lens - (this is called
accommodation). It relaxes to flatten
the lens for distance vision; for close
work it contracts rounding out the lens.
Everyone will develop an eye condition
called presbyopia. As we age, the
ciliary muscle and crystalline lens lose

EYELENS
It is a convex lens made of a
transparent and flexible
material like a jelly made of
proteins.
It forms of a real image of
the objects on the retina of
the eye

Power Of Accommodation
Ability of eye lens to adjust
its focal length.
For Young Adult P= 4D

Near Point (Least Distance Of

Distinct Vision)
Its is the minimum distance at
which eye can see objects very
clearly without any strain. Its
value is 25 cm.
Far Point
It is the farthest point up to which
eye can see objects very clearly.
Its value is

RETINA
The retina is the film of the
eye. It converts light rays into
electrical signals and sends
them to the brain through the
optic nerve. The sides of the
retina are responsible for our
peripheral vision. The center
area, called the macula, is

The retina is where most the

problems leading to vision loss
Occur.
Three of the leading causes of
blindness, from retina damage,
are Retinitis Pigmentosa,
Macular Degeneration and
Diabetic Retinopathy.

Retinitis
Pigmentosa

Macular
Degeneration

Diabetic Retinopathy.

OPTIC NERVE
Each optic nerve has about
1.2 million nerve fibers. This
is the cable connecting the
eye to the brain.

SCLERA
The sclera is the white, tough
wall of the eye. It along with
internal fluid pressure keeps
the eyes shape and protects its
delicate internal parts.

CHOROID
The choroid is a layer of
blood vessels between the
retina and sclera; it supplies
blood to the retina. It keeps
the interior eye dark.

BLIND SPOT
The region on the retina
where there is no cones and
rods at the part where the
optic nerve leaves the
eyeball.

YELLOW SPOT OR MACULA

It is situated at the Centre
of the retina. Its function is
to form an extremely clear
image.

VITREOUS HUMOUR
Thevitreous humourorvitreous humoris the
cleargelthat fills the space between
thelensand theretinaof theeyeballof
humans and othervertebrates. The vitreous is
the transparent, colourless, gelatinous mass
that fills the space between the lens of the eye
and the retina lining the back of the eye. It is
produced by certain retinal cells. It contains
very few, no blood vessels, and 98-99% of its
volume is water with salts, sugars, vitrosin,
and a wide array of proteins in micro amounts.

AQUEOUS HUMOUR
Theaqueous humouris a clear,
gelatinous fluid similar to plasma,
but containing low-protein
concentrations. It is secreted from
the ciliary epithelium, a structure
supporting the lens.It is located in,
the space between thelensand
thecornea.

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MYOPIA
Myopia is a condition of the eye where
the light that comes in does not
directly focus on the retina but in front
of it. This causes the image that one
sees when looking at a distant object
to be out of focus but in focus when
looking at a close object.
Myopia presents with blurry distance
vision, but generally gives good near
vision. In high myopia, even near

CAUSES
Mostnearsightedness is caused by
a natural change in the shape of
the eyeball.
Other than the natural change in
the shape of the eyeball, there are
a few rare causes of
nearsightedness. These are:

 Pathological myopia, in which the

back of the eyeball continues to grow
longer after reaching normal adult
size.
Secondary myopia, which may
develop as a result of many
conditions, including premature
birthand a number ofeyediseases.
In some cases, nearsightedness may
be caused by eye problems such as
cataracts,etc.

TREATMENT
There is no universally
accepted method of preventing
myopia.Commonly attempted
preventive methods include
wearing reading glasses, eye
drops and participating in more
outdoor activities

HYPERMETROPIA
Hypermetropia, is
adefectofvisioncaused by an
imperfection in theeye causing
difficultyfocusingon near
objects. Farsightedness occurs
when light entering theeye
through the lens is focusedbehind
the retinainstead of directly on it.

CAUSES
Hyperopia can be caused by
infections, injuries, migraines,
aging or genetics. This is caused
by an eye that is too short, whose
cornea is not curved enough, or
whose lens sits farther back in the
eye than normal.Farsightedness is
also inherited.

TREATMENT
Minor amounts of hyperopia are
sometimes left uncorrected.
However, larger amounts may be
corrected withconvex
lensesineyeglassesorcontact
lenses. Convex lenses have a
positivedioptric value, which
causes the light to focus closer
than its normal range.

PRESBYOPIA
Presbyopiais a condition where
theeyeexhibits a progressively diminished
ability to focus on near objects with age.
Presbyopias exact mechanisms are not
known with certainty; the research evidence
most strongly supports a loss of elasticity of
thecrystalline lens, although changes in the
lenss curvature from continual growth and
loss of power of theciliary muscles(the
muscles that bend and straighten the lens)
have also been considered as its cause.

SYMPTOMS OF PRESBYOPIA
The first symptoms most people notice
are difficulty reading fine print,
particularly in low light
conditions,eyestrainwhen reading for
long periods, blur at near or
momentarily blurred vision when
transitioning between viewing
distances.These symptoms are usually
first noticed between the ages of 40
and 50.

TREATMENT
Corrective lenses provide a range of
vision correction, some as high as +4.0
diopter.Contact lensescan also been
used to correct the focusing loss that
comes along with presbyopia.
Controversially, eye exercises have
been touted as a way to delay the
onset of presbyopia, but their
effectiveness has not been
demonstrated in medical research.

CATARACT
The lens of the eye is normally clear. It acts
like the lens on a camera, focusing light as it
passes to the back of the eye.
Until a person is around age 45, the shape of
the lens is able to change. This allows the
lens to focus on an object, whether it is close
or far away.
As we age, proteins in the lens begin to break
down and the lens becomes cloudy. What the
eye sees may appear blurry. This condition is
known as a cataract.

Factors that may speed up cataract formation

are:
Diabetes
Eye inflammation
Eye injury
Family history of cataracts
Radiation exposure
Smoking
Surgery for another eye problem
Too much exposure to ultraviolet light
(sunlight)
In many cases, the cause of cataract is
unknown.

SYMPTOMS
Adult cataracts develop slowly and
painlessly. Vision in the affected eye or
eyes slowly gets worse.
By age 75, most people have cataracts
that affect their vision.
Visual problems may include the
following changes:
Being sensitive to glare
Cloudy, fuzzy, foggy, or filmy vision

 Difficulty seeing at night or in

dim light
Double vision
Loss of color intensity
Problems seeing shapes
against a background or the
difference between shades of
colors
Seeing halos around lights

TREATMENT
The following may help
people who have an early
cataract:
Better eyeglasses
Better lighting
Magnifying lenses
Sunglasses

 As vision gets worse, you may

need to make changes around the
home to avoid falls and injuries.
The only treatment for a cataract
is surgery to remove it. Surgery is
done if you cannot perform
normal activities, such as driving,
reading, or looking at computer or
video screens, even with glasses.

ASTIGMATISM
Astigmatism is a type of
refractive error of the eye.
Refractive errors cause
blurred vision and are the
most common reason why a
person goes to see an eye
professional.

Causes, incidence, and risk factors

People are able to see because the
front part of the eye is able to bend
(refract) light and point it to the back
surface of the eye, called the retina.
Changes in the length of the eye, or
the shape of either the lens or the
cornea make it more difficult for the
eyes to focus light. If the light rays are
not clearly focused on the retina, the
images you see may be blurry.

With astigmatism, the cornea (the

clear tissue covering the front of
the eye) is abnormally curved,
causing vision to be out of focus.
The cause of astigmatism is
unknown. It is usually present
from birth, and often occurs
together with nearsightedness or
farsightedness.
Astigmatism is very common. It
sometimes occurs after certain

SYMPTOMS
Astigmatism makes it difficult
to see fine details, either close
up or from a distance.

TREATMENT
Mild astigmatism may not need to
be corrected.
Glasses or contact lenses will
correct astigmatism.
Laser surgery can help change the
shape of the cornea surface to
correct astigmatism, along with
nearsightedness or farsightedness.