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Human Eye

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Human Eye

  1. 1. THE HUMAN EYE
  2. 2. Anatomy of the Human Eye
  3. 3. Layers of the Eye <ul><li>Sclera: outer white layer; maintains shape of eye; muscles attached control eye movement </li></ul><ul><li>Choroid: contains blood vessels </li></ul>
  4. 4. Sclera
  5. 5. Chambers & Fluids of Eye <ul><li>Liquids (humour): </li></ul><ul><ul><li>gives shape to eye </li></ul></ul><ul><ul><li>Help refract light rays </li></ul></ul>
  6. 6. Regulating Amount of Light <ul><li>Iris </li></ul><ul><li>Pupil </li></ul>
  7. 7. contracted pupil dilated pupil
  8. 8. Regulating amount of light aperture in camera hole of iris where light enters eye black centre Pupil diaphragm in microscope open and closes to control the amount of light entering eye coloured ring Iris Analogy Function Description Parts
  9. 9. Focusing Light Rays <ul><li>Cornea </li></ul><ul><li>Lens </li></ul><ul><li>Ciliary muscle </li></ul>
  10. 10. Focusing Light Rays <ul><li>Light rays from distant objects enter the eye parallel to one another </li></ul><ul><li>Light rays from close objects diverge . </li></ul>
  11. 11. Nearby Objects Distant Objects
  12. 12. Accommodations Changing the shape of the eye lens to keep objects in focus
  13. 13. Image Production <ul><li>Retina </li></ul><ul><li>Optic nerve </li></ul><ul><li>Optic disc </li></ul><ul><li>Macula lutea </li></ul><ul><li>Fovea centralis </li></ul>
  14. 14. Retina <ul><li>At the back of the eye </li></ul><ul><li>Consist of 2 types of light-sensitive cells: rods and cones </li></ul><ul><li>Converts light signal into an electrical signal that is transmitted to the brain through the optic nerve </li></ul>
  15. 15. Rods and Cones <ul><li>rod cells: light sensors </li></ul><ul><ul><li>120 million </li></ul></ul><ul><ul><li>Functions in less intense light </li></ul></ul><ul><ul><li>Used in peripheral vision </li></ul></ul><ul><ul><li>Responsible for night vision </li></ul></ul><ul><ul><li>Detects black, white and shades of grey </li></ul></ul><ul><li>cone cells: detects colour </li></ul><ul><ul><li>7 million </li></ul></ul><ul><ul><li>Highest concentration at fovea centralis </li></ul></ul><ul><ul><li>Functions best in bright light </li></ul></ul><ul><ul><li>Perceives fine details </li></ul></ul><ul><ul><li>3 types of cone cells, each sensitive to one of the three primary additive colours: red, green, and blue </li></ul></ul>
  16. 16. Macula Lutea <ul><li>Small yellowish area of the retina near the optic disc (“yellow spot”) </li></ul><ul><li>Area that provides the most acute vision (clear vision) </li></ul><ul><li>When the gaze is fixed on any object, the centre of the macula, the centre of the lens, and the object are in a straight line </li></ul>http://www.britannica.com/EBchecked/topic/355512/macula-lutea
  17. 17. Fovea Centralis (Central Fovea) <ul><li>A pit in the centre of the macula lutea </li></ul><ul><li>Contains no rod cells </li></ul><ul><li>Has high concentration of cone cells </li></ul><ul><li>Recall: cones are associated with colour vision and perception of fine detail </li></ul><ul><li>No blood vessels to interfere with vision </li></ul><ul><li>Provides sharp detailed vision (e.g. needed during reading, driving etc.) </li></ul>http://www.britannica.com/EBchecked/topic/355512/macula-lutea
  18. 18. Optic Nerve <ul><li>Nerve cells that transmit message from light-sensitive cells in retina to the brain </li></ul>
  19. 19. Activity: The reappearing dot <ul><li>Draw an X on a piece of paper. Then draw a dot 6 cm to the right of the X. </li></ul><ul><li>Cover your left eye with your left hand. </li></ul><ul><li>Hold the paper with your right hand at arms length away. </li></ul><ul><li>Focus your right eye on the X but keep the dot in your peripheral vision. </li></ul><ul><li>Slowly move the paper towards your face and notice when the dot “disappears” and “reappears”. </li></ul>
  20. 20. Blind Spot <ul><li>Optic disc : where the optic nerves converge and exit the eye </li></ul><ul><li>No light-sensitive cells to detect light rays </li></ul><ul><li>Results in a break in the visual field, known as a blind spot </li></ul>
  21. 22. Right Eye http://neil.fraser.name/news/2008/11/22/ Fovea Centralis Blind spot
  22. 23. Producing an Image <ul><li>The converging lens produces an inverted image which the brain interprets as being upright </li></ul>
  23. 24. Producing an Image <ul><li>Cells on retina trigger a nerve impulse </li></ul><ul><li>Nerve cells sends an electrical signal to the brain via the optic nerve </li></ul>
  24. 25. Video: How the Human Eye Works http://www. youtube .com/watch?v= JadaWSDxBYk
  25. 26. Vision Problems <ul><li>Myopia (near sightedness) </li></ul><ul><li>Hyperopia (far sightedness) </li></ul><ul><li>Presbyopia </li></ul><ul><li>Astigmatism </li></ul>
  26. 28. Myopia (near-sightedness) <ul><li>inability of the eye to focus light from distant objects </li></ul><ul><li>see close objects clearly </li></ul><ul><li>image focuses in front of the retina </li></ul>
  27. 29. Myopia (near-sightedness) <ul><li>Develops in childhood and progressively worsens </li></ul><ul><li>Tends to stabilize in adulthood </li></ul><ul><li>Has a genetic component </li></ul><ul><li>Affects a major part of the population </li></ul>
  28. 31. Myopia (near-sightedness) <ul><li>Cause: </li></ul><ul><li>Distance between lens and retina is too long (long eyeball) </li></ul><ul><li>Cornea & lens converge light too strongly (strong refractive power) </li></ul>
  29. 32. Myopia (near-sightedness) <ul><li>Corrected with a diverging lens </li></ul><ul><li>Negative meniscus: lens shape where edge of lens is thicker than the middle but modified from a basic diverging lens to make it more cosmetically appealing </li></ul>
  30. 33. Myopia (near-sightedness) negative meniscus (-): a diverging lens Image focuses BEFORE reaching the retina
  31. 34. Types of Lenses Different types of lenses can correct different types of vision. Converging lens Diverging lens
  32. 36. Hyperopia (far sightedness) <ul><li>inability of the eye to focus light from near objects </li></ul><ul><li>no difficulty seeing distant objects </li></ul><ul><li>Babies are born slightly hyperopic. As eye grows, condition fixes itself. </li></ul><ul><li>image focused behind retina </li></ul>
  33. 38. Hyperopia (far sightedness) <ul><li>Cause: </li></ul><ul><li>Distance between lens and retina is too small (short eyeball) </li></ul><ul><li>Cornea & lens is too weak (doesn’t diverge rays enough) </li></ul>
  34. 39. Hyperopia (far sightedness) <ul><li>Corrected with converging lens </li></ul><ul><li>Positive meniscus: lens shape where middle part of lens is thicker than the edge but modified from a basic converging lens to make it more cosmetically appealing </li></ul>
  35. 40. Hyperopia (far-sightedness) positive meniscus (+): converging lens Images focused BEHIND the retina.
  36. 41. Types of Lenses Different types of lenses can correct different types of vision. Converging lens Diverging lens
  37. 43. Presbyopia <ul><li>A form of hyperopia (far sightedness) that occurs with age </li></ul><ul><li>Cause: eye lens losing elasticity </li></ul><ul><li>Not a result of eyeball being too short </li></ul><ul><li>Correct with converging lens </li></ul>
  38. 45. Astigmatism <ul><li>Irregular shaped cornea “football” </li></ul><ul><li>Two focus points </li></ul>
  39. 46. Astigmatism Astigmatism is a vision problem that results from a cornea that has an irregular shape
  40. 47. Video: Laser Eye Surgery http://www.youtube.com/watch?v=0V4I2xzwGd4
  41. 48. Lab: Cow Eye Dissection <ul><li>Bring your goggles! Gloves will be provided. </li></ul><ul><li>Video: Exploratorium Cow Eye Dissection </li></ul><ul><li>http://www.exploratorium.edu/learning_studio/cow_eye/video_big_all.html </li></ul><ul><li>http://www.teachersdomain.org/resource/lsps07.sci.life.stru.coweye/ </li></ul><ul><li>Video: Bill Nye </li></ul><ul><li>http://www.youtube.com/watch?v=cFVbLnXWn6A&feature=related </li></ul>

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