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12.3– The Human Eye

12.3– The Human Eye. pg. 506 - 511. The Eye by Bill Nye. The Eyeball. Eye Anatomy. 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.

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12.3– The Human Eye

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  1. 12.3– The Human Eye pg. 506 - 511

  2. The Eye by Bill Nye • The Eyeball

  3. Eye Anatomy • 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

  4. Eye Anatomy • 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

  5. Eye Anatomy • 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

  6. Human Vision • 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

  7. Accommodation • 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

  8. Focusing Problems • Accommodation does not always work well. This results in an inability to focus on objects and thus producing blurred vision

  9. Hyperopia (far-sightedness) • 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

  10. Hyperopia (far-sightedness) • 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

  11. Presbyopia • 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

  12. Myopia (near-sightedness) • 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

  13. Astigmatism • blurred or distorted vision • caused by an incorrectly shaped cornea • corrective lenses or laser eye surgery can be used to correct astigmatism

  14. Homework • Read pg. 506 - 511 • Do #5, 7, 8 on pg. 511 • Study for your Physics Unit Test (Chapters 10, 11, 12)

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