The eye

• Accommodation


  The ability to change the shape of the lens to focus on near or distant objects
• Accommodation


  1. Ciliary muscle contracts

  2. Suspensory ligaments loosen

  3. Lens becomes thicker

  4. Lens refracts light more strongly
• Focusing on distant objects

  1. Ciliary muscle relaxes

  2. Suspensory ligaments are pulled tight

  3. Lens becomes thinner

  4. Lens refracts light less strongly
• Focusing on near objects

  1. Ciliary muscle contracts

  2. Suspensory ligaments loosen

  3. Lens becomes thicker

  4. Lens refracts light more strongly
• Hyperopia (long-sightedness)


  People with long sight have no problem focusing on distant objects but cannot focus on nearby objects
• Causes of hyperopia


  • Eyeball too short so light focused behind retina
  • Lens becomes less elastic so cannot become thick enough
• Treatment for hyperopia


  Glasses with convex lenses to partially focus light before it enters the eye
• Myopia (short-sightedness)


  People with short sight can focus on nearby objects but cannot focus on distant objects
• Causes of myopia


  • Eyeball too long so light focused in front of retina
  • Lens too thick
• Treatment for myopia


  • Glasses with concave lenses to partially unfocus light before it enters the eye
  • Contact lenses
  • Laser surgery to change cornea shape