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THE EYE

THE EYE. The Eye. Is an optical instrument that we use to see around us. It acts very much like a camera It uses a converging lens to focus the image on a sensor Lets more or less light in when needed Allows us to view the image. Eye and Camera. Eye Anatomy.

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THE EYE

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  1. THE EYE

  2. The Eye • Is an optical instrument that we use to see around us. • It acts very much like a camera • It uses a converging lens to focus the image on a sensor • Lets more or less light in when needed • Allows us to view the image

  3. Eye and Camera

  4. Eye Anatomy • Iris  opens or closes to let more or less light in • Cornea and Lens  act to converge light rays to create an image • Retina  screen where image is located. Creates an electrical signal to be interpreted by the brain. • Optic nerve  transmits the electrical signal created by the retina to the brain so that we “see”

  5. Blind Spot – Try It!

  6. Blind Spot • There are no light sensitive areas where the optic nerve connects to the retina • If an image is formed on the blind spot we cannot see it • The reason we normally do not notice our blind spots is because our other eye compensates and “fills in” the gap

  7. Eye vs. Brain • We don’t actually see with our eyes • We use our eyes to create an image on our retina • The eye uses a converging lens so the image produced on the retina is always smaller, inverted and real

  8. Computer Demonstration – Showing smaller inverted image with converging lens • http://www.phy.ntnu.edu.tw/ntnujava/index.php?PHPSESSID=643ae5051e223f1f696d419c040b986d&topic=48.msg297#msg297

  9. These images are sent via electrical signals to the brain to be interpreted • The brain then takes the inverted image and flips it so what we “see” is an upright image

  10. Camera Lens vs. Eye Lens • Both cameras and eyes cannot move their “screen” • Cameras move their lens to focus an image • Eyes cannot move their lens • Eyes instead change the shape of their lens using ciliary muscles which alters the focal length allowing focusing on the retina • This is called Accommodation Computer Simulation to show moving screen, camera lens and Eye

  11. Accommodation

  12. Focusing • Some people cannot focus incoming light rays as well as they should, creating blurred images • This can happen when objects are far away or near

  13. Myopia (Near-sightedness) • The eye can focus light ray from nearby objects but cannot see objects at a distance • Caused by a too-long eye ball or to much converging of light by the lens and cornea • Light is focused in front of the retina

  14. A diverging lens is needed to spread apart the light rays so that they create an image at the retina • The diverging ray is altered slightly and called a negative meniscus so that it looks better Computer Simulation to show Myopia

  15. Hyperopia (Far-sightedness) • Person can see distant objects (a) but cannot see near objects (b) • The eye cannot refract light well enough to create a focused image on the retina • Image is created behind the retina  blurry • Usually caused by the eye ball being too short Computer Demonstration to show Hyperopia

  16. Converging Lens – Positive Meniscus • Since light isn’t refracted well enough (a), far-sighted people can use a converging lens to help out (b) (a) (b)

  17. Positive Meniscus • The converging lens is altered to create a positive meniscus • A positive meniscus is much more appealing shape • It is still a converging lens because it is thicker in the middle then on the edges

  18. Presbyopia • A form of farsightedness (people find it hard to read small print) • Usually comes with age as eye loses its ability to accommodate • Also corrected with converging lenses Demonstration at front

  19. Video • Nearsightedness and Farsightedness Video

  20. Contact Lenses • Have the same function as glasses • Can be shaped to form a positive or negative meniscus • Placed on the cornea of the eye (invisible) • Can also be used to change the eye colour

  21. Laser Eye Surgery • Laser Eye Surgery Video

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