Focussing and Accommodation

• When looking at a close object the lens is thick
• when looking at a distant object the lens is thin.
• The lens changes shape using the suspensory ligaments and ciliary muscles.
• When the ciliary muscles relax, the suspensory are pulled tightly and the lens is thin.
• When the ciliary muscles contract, the suspensory muscles are loose and the lens is thick.
• When looking at a close object the light waves diverge.
• When looking at a distant object the light waves are not very diverging.
• Short sightedness

  • Can see close but not far
  • Light is refracted too much
• What are two reasons for short sightedness?


  • Cornea/lens is too thick
  • Eyeball is too long
• Long sightedness 


  • Can see far not close
  • Light not refracted enough
• What are two reasons for long sightedness?


  • Cornea/lens is too thin
  • Eyeball too long
• How do you fix short sightedness? 


  Concave lens
• How do you fix long sightedness?


  Convex lens