Light & Sight
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Transcript of Light & Sight
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LIGHT & SIGHT
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What is light?
Light comes in two forms
as WAVES or PARTICLES(photons).
Light must be produced by
a source, but it is thereflection of light thatenables us to see objects.
Where light is blockedfrom reflecting it producesshadows which are theabsence of light, as isdarkness.
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How do we see?
The human eye is a complexsystem that records light andturns it into an electrical
signal which is interpreted bythe brain.
The different parts of thehuman eye function together
to produce an image. If oneof these parts is damaged,then we are unable to see.
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The Human Eye
The eye is divided
into parts whichcontrol the entry of
light or capture it to
send to the brain
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The Pupil and Iris
The iris is a ring ofmuscle around avariable size openingwhich is the pupil.
The iris consists ofconcentric muscleswhich contract andrelease to make thepupil smaller or larger.
The pupil itself looksblack because it is ahole.
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The Lens
The lens is a fluidfilled structure thatfocuses light fromthe cornea on the
retina. The lens is held in
place by ligamentswhich areconnected to the
ciliary muscles.These can alter thelens shape, calledaccommodation.
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Short or Long Sightedness
Sometimes there is aproblem with the lens thisleads to long sightedness(can see far but not near)and short sightedness (can
see close but not far). Glasses account for the
inability of the lens to focuscorrectly and allow theperson to see clearly. A
convex lens will correct longsightedness and a concavelens will correct shortsightedness.
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The Interior of the Eye
The eye is surrounded by a tough membrane
which hold the shape of the eye in
conjunction with the vitreous humour which is
a thick gel-like water based substance which
gives the eye structure by putting pressure on
the external membrane. The eye is lined with
another membrane called the retina.
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The Retina
The retina is the lining of the eye. Itis rich in blood vessels which form apattern unique to each humanbeing.
The retina is covered in specialised
cells called the rods and cones,which are different types ofphotoreceptors.
There are two specific features onthe retina the fovea and macula.
The macula is the central point offocus and allows us to see detail.
The fovea is completely free ofrods.
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Rods and Cones
Rods are necessary
for peripheral vision
and seeing in dim
light.
Cones are necessary
for direct sight and
seeing in bright light.
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The Optic Nerve
The optic nerve takes the invertedimage from the retinal receptorsand converts it into an electricalsignal. This is sent via the nervecells in the optic nerve to the brain
which translates and turns theimage the right way round.
Where the optic nerve comes intothe eye we have a blind spot. Thiscompensated for as our two eyeswork in conjunction with each
other to produce a threedimensional image.
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Stereoscopic Vision
Humans have stereoscopic
vision as we have two eyes
that function together.
Each image from each eye is
seen simultaneously and
processed simultaneously into
a single image. This gives usout depth perception and
awareness of 3D objects.
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Try It!
Place one hand over each eye in turn and
notice where the blind spot is.
Try closing one eye and try to grasp an object
that is close to you. Now try one far from you.
Get someone to approach you from behind
and at an angle. See how much you can see.
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Optical Illusions
Because of our depth perception, our eyes can
be tricked. Try looking at these images and see
what happens.
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