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How we see (Brain and senses)

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How we see (Brain and senses) Powered By Docstoc
					Brain            and   senses

How we see
Inside your eye is a lens like the lens
of a camera. Its job is to focus light
on the back of your eye so you can
see things clearly.
                                                    .
                         object and           r eye
                   ff an            enters you
              ts o
        f lec
                 re
            ht
        Lig




                           The eye is filled with a
                           semi-solid jelly.




Optic
nerve

                                   The lens is clear and                                     An object
                                   flexible. It focuses on
The retina                            things by changing             The pupil is a hole
contains cells                                      shape.           that lets light into
that sense                                                           the eye.
light.




How your eye works
Light from an object enters your eye                                 Seeing in colour
through the pupil. It passes through                                 Your eyes contain millions
the lens, and makes an upside down                                   of cells. Cone cells give you
                                                                       colour vision but don’t
image on the retina at the back of                                        work well in dim light.
your eye. Cells in your eye send                                              Rod cells work well
messages down the optic nerve                                                   in dim light but
to your brain. Your brain                                                          see everything
                                                                                      in shades
flips the image back the                                                                 of grey.
    right way round.
40
                           What is an eye specialist who tests eyesight called?
                                                                                      How we see
                                                                                       no
Blurry vision
                                                                               be r? If t, you
Sometimes an eyeball is the wrong shape.                                   m                      m




                                                                   u
The lens cannot focus light on the retina and




                                                                                                   ay
                                                                       n
everything is blurry. Glasses make the light




                                                           n you see a




                                                                                                       be c
focus in the right place to make things clear.




                                                                                                           olour
Short eyeball
If you have a short
eyeball you will have




                                                                                                                 bli
difficulty seeing things




                                                         Ca
close up. This is called




                                                                                                       d             n
long sightedness.                                                                                  .

Long eyeball                                                 Colour blindness
It is difficult to see                                       Some people cannot tell certain
objects that are far away                                    colours apart, especially red
when your eyeball is too
long. This is known as
                                                             and green. This is called colour
short sightedness.                                           blindness. It is more common
                                                             in men than women.
                                                                                                Glasses bend

       g et i n t o i t
                                                                                           the light entering
                                                                                               your eye so it
                                                                                              focuses on the
          Close one eye                                                                                retina.
                                       Contact lenses
    and hold a finger in front
                                       These work like
  of your nose. Open that eye
                                      mini glasses and
    and close the other one.
                                       sit directly in
      The finger appears to
                                        front of the
      move! Each eye sees
                                    eye. They’re a
        things differently.
                                    bit fiddly, but
                             once they’re in you
                           can’t feel them at all.


                      Contact lenses are
                      made of very thin
                      plastic.




                                             An optician.                                                 41

				
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posted:10/10/2012
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