The cornea is the clear dome-shaped surface at the front of the eye that acts as the first lens. Light passes through the pupil, which is controlled by the iris, and hits the retina where it is converted to electrical signals sent to the brain. The lens, located behind the iris, changes shape to focus light onto the retina. Common eye disorders include cataracts, which cloud the lens; glaucoma caused by increased fluid pressure damaging the optic nerve; and retinal disorders affecting the light-sensitive tissue at the back of the eye.

3. Understanding Vision
Lens
Focal
Point
Cornea

4. The cornea is a clear, dome-shaped
surface that covers the front of
the eye. It is the first and most
powerful lens in the eye's optical
system. To keep it transparent the
cornea contains no blood vessels.
Tears that flow over it and aqueous
humor in the chamber behind it keep

5. Pupil

The pupil is the hole in the center of the iris that
light passes through. The iris muscles control its size.
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 used for
our fine central vision and color vision.

6. 
 This
Iris
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 exposure,
the iris of the eye helps protect the sensitive
retina.

7. 
Sc l e r a
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.

8. 
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Lens
Transparent body enclosed in an elastic capsule
Made up of proteins and water
Consists of layers, like an onion, with firm nucleus, soft
cortex
Gradient refractive index (1.38 - 1.40)
Young person can change shape of the lens via ciliary
muscles
Contraction of muscle causes lens to bulge
At roughly age 50, the lens can no longer change shape
Becomes more yellow with age: Cataracts
The graph on the right shows the optical density (-log
transmittance) of the lens as a function of wavelength. The
curves show the change in density with age. More short
wavelength light is blocked at increases ages.

9.  ciliary
body (muscles)
 *circular
muscle that surrounds the
edge of the lend
* connected to the lens by suspensory
ligaments
*changes the shape of the lens

10.  The
blind spots in each eye are aligned symmetrically
so that most of the time, one eye’s field of vision will
compensate for the loss of vision in the other. The
diagram above shows where the blind spots are
located.

11. 


To find the eye’s blind spot, you can do the
following tests.
In order to find the blind spot of the right
eye, it is necessary to close the left eye,
focus the right eye on a single point, and see
if anything vanishes from vision some 20
degrees right of this point. The following
diagram has a set of characters on the left
hand side, and black circle on the
right.Keeping your head motionless, with the
right eye about
3 or 4 times
as far from the page as the length of the
red
line, look at
each
character in turn, until
the
black
circle vanishes.
optic nerve

13.  Some
eye problems are minor and
fleeting. But some lead to a
permanent loss of vision. Common
eye problems include,Cataracts clouded lenses
 Glaucoma - damage to the optic
nerve from too much pressure in
the eye.Retinal disorders problems with the nerve layer at
the back of the eye.Conjunctivitis an infection also known as pinkeye.
 Your best defense is to have

14. 
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Cataract
A cataract is a clouding of the lens in your eye. It affects your
vision. Cataracts are very common in older people. By age 80,
more than half of all people in the United States either have a
cataract or have had cataract surgery.
Common symptoms are
Blurry vision
Colors that seem faded
Glare
Not being able to see well at night
Double vision
Frequent prescription changes in your eye wear
Cataracts usually develop slowly. New glasses, brighter lighting,
anti-glare sunglasses or magnifying lenses can help at first.
Surgery is also an option. It involves removing the cloudy lens
and replacing it with an artificial lens. Wearing sunglasses and a
hat with a brim to block ultraviolet sunlight may help to delay
cataracts.

15. 
Disorders
 The
Retinal
retina is a layer of tissue in the
back of your eye that senses light
and sends images to your brain. In
the center of this nerve tissue is the
macula. It provides the sharp, central
vision needed for reading, driving and
seeing fine detail.
 Retinal disorders affect this vital
tissue. They can affect your
vision, and some can be serious
enough to cause blindness. Examples
are

16. 
Glaucoma
Glaucoma damages the eye's optic
nerve. It usually happens when the fluid
pressure inside the eyes slowly
rises, damaging the optic nerve. Often
there are no symptoms at first, but a
comprehensive eye exam can detect it.
 People at risk should get eye exams at
least every two years.
 Early treatment can help protect your
eyes against vision loss. Treatments usually
include prescription eyedrops and/or
surgery.
