Eye defects

• What is accommodation 


  Process of changing shape of lens to focus on near or distant objects
• What happens when you focus on near objects

  Lens becomes thicker -> light rays refract more strongly
• What happens when you focus on distant objects

  Lens pulled thin -> light rays refract slightly
• What are the 3 eye defects

  • Cataracts
  • Short sightedness
  • Long-sightedness
• What is a cataract

  • Cloudiness in lens -> build up of protein inside lens
  • So cloudy vision
  • Experience colours being less vivid
  • Difficulty seeing bright lights
• How do you treat cataracts

  Removing lens + replacing with plastic lens
• What are 2 common defects of the eye

  Myopia + hyperopia
• What is myopia


  • Short-sightedness -> can't see distant objects
  • In both cases -> rays of light don't focus on retina so no clear image formed
• What is myopia caused by

  • Eyeball being too elongated so distance between retina + lens too big
  • Lens being too thick + curved -> light focuses IN FRONT of the retina
• How do you short-sightedness

  Placing a concave lens in front of the eye
• What is hyperopia 


  • Longsightedness -> cant focus on near objects
• What is hyperopia caused by

  • Eyeball being too short -> distance between lens + retina too small
  • Loss of elasticity in lens -> not thick enough to focus -> age related + light focuses BEYOND retina
• How do you fix hyperopia

  Putting a convex ens in front of the eye
• Describe the convex + concave lens 


  Here

  
• What are alternatives to wearing spectacle lenses

  • Hard + soft contact lenses
  • Laser surgery -> changes shape of cornea
  • Replacement lens in eye
• How do contact lenses work

  • Float on surface of cornea
  • Works like spectacle lenses by focusing + refracting light
• How does laser surgery work

  • Reshapes cornea surgically
  • Common for myopia but can be used for hyperopia
• How does replacement lens

  • Implanting artificial lenses in front of original lens
  • Through a small cut in cornea to correct eye defects