pg. 506 - 511. the eyeball the eyeball iris: coloured part of the eye that opens and closes to let...
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12.3– The Human Eyepg. 506 - 511
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The Eyeball
The Eye by Bill Nye
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Iris: coloured part of the eye that opens and closes to let in more or less light. In the centre you find the pupil
Pupil: opening where light enters the eye Cornea: Transparent bulge on top of the
pupil
Eye Anatomy
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Lens: Clear part behind the iris◦ NOTE: Both the cornea & lens focus light &
cause it to converge on the back of the eye. Retina: Inner lining of eye that is made of
light-sensitive cells, called rods and cones. These cells receive light rays, process them & send electric signals to the optic nerve
Eye Anatomy
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Optic Nerve: The nerve at the back of the eye that is attached to the retina. It transmits the electrical impulses from the retina to the brain◦ Since there are no light sensitive cells here, it
creates a blind spot but each eye compensates for the other
Eye Anatomy
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Light entering our eyes is refracted The lens acts like a converging lens that
produces a smaller, real, inverted image on the retina.
Electrical impulses travel through the optic nerve to the brain
Brain flips the inverted image so what we see is upright
Human Vision
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Accommodation is the changing of shape of the lens by ciliary muscles to allow a sharp focused image to form on the retina
By changing the eye’s shape, the focal length changes, allowing us to focus on distant and nearby objects
Accommodation
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Accommodation does not always work well. This results in an inability to focus on objects and thus producing blurred vision
Focusing Problems
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Inability to focus light from nearby objects (can see distant objects)
Light is focused behind the retina Caused by a thin cornea; or an eyeball that
is too short
Hyperopia (far-sightedness)
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Corrected using converging contact lenses or eye glasses to help refract the light
A modified form of the converging lens, called a positive meniscus is used because it is thinner & more visually appealing than a basic converging lens
Hyperopia (far-sightedness)
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Form of far-sightedness caused by a loss of accommodation as a person ages
Eye loses its elasticity as we grow older Corrected using glasses with converging
lenses
Presbyopia
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Inability of the eye to focus light from distant objects (can see nearby objects)
Light is focused in front of the retina A modified form of the diverging lens, called
a negative meniscus, is used
Myopia (near-sightedness)
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blurred or distorted vision
caused by an incorrectly shaped cornea
corrective lenses or laser eye surgery can be used to correct astigmatism
Astigmatism
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Read pg. 506 - 511 Do #5, 7, 8 on pg. 511 Study for your Physics Unit Test (Chapters 10, 11, 12)
Homework