topic 2-The eye

• 1. the cornea bends light into the eye
  2. the iris controls how much light enters the pupil
  3. the lens also refracts light, focusing it onto the retina
  4. the retina is the light-sensitive part and its covered in rod and cone cells which detect light
  5. rods are more sensitive to dim light but cant sense colour
  6. cones are sensitive to different colours but are not good in dim light
• When looking at distant objects:

  1. The cilliary muscles relax, which allow the suspensory ligaments to contract
  2. this pulls the lens into a less rounded shape so light is refracted less
• when looking at close object:

  1. The cilliary muscles contract, and suspensory ligaments relax
  2. the lens becomes a more rounded shape so light is refracted more
• Long-sighted people are unable to focus on near objects:

  1. this occurs when the lens is the wrong shape and doesn't bend the light enough or the eyeball is too short
  2. light from near objects is brought into focus behind the retina
  3. convex lenses are used
• Short-sighted people are unable to focus on distant objects

  1. this occurs when the lens is the wrong shape and bends the light too much
  2. Light from distant objects is brought into focus in front of the retina
  3. concave lenses are used
• people with cataracts are likely to have blurred vision
• a cataract can be treated by replacing the faulty lens with an artificial one
• there is no cure for color blindness because cone cells cannot be replaced
• in bright light the pupil is constricted
• pupil constriction:

  • circular muscles contract
  • radial muscles relax
• in low light the pupil is dilated
• pupil dilation

  • circular muscles relax
  • radial muscles contract
• looking at close objects

  • ciliary muscles contract
  • suspensory ligaments relax
  • lens gets fatter and more rounded
• looking at objects that are far away

  • ciliary muscles relax
  • suspensory ligaments contract
• long sighted

  • light bends behind the retina
  • convex lenses used
• short sighted

  • refracts light too much
  • concave lenses used
• Long sighted: Hyperopia
• short sighted: myopia