The eye

• Pupil


  Small hole that lets ligt into the eye
• Iris


  Controls the size of the pupil so can control how much light enters the eye
• Cornea and lens 


  Refract light rays as they enter the eye
• Ciliary muscles and suspensory ligaments


  Control the shape of the lens to focus the light
• Retina


  Contains receptors that are sensitive to light intensity and colour
• Optic nerve


  Carried impulses from receptors in the retina to the brain
• Sclera


  Fibrous outer wall that supports and protects the eye
• In bright lights

  Iris contracts to make the pupil smaller

  Less light allowed into the eye
• in dim light

  Iris relaxes to make the pupil bigger

  Allows more light into the eye
• The eyes lens chnages shape to help it focus on both near and far away objects


  known as accommodation
• To focus on a near object

  Ciliary muscles contract

  Suspensory ligaments loosen

  Makes lense thicker

  so light rays refracted more strongly
• To focus on a far away object

  Ciliary muscles relax

  Suspensory ligaments tighten

  Makes lens thinner

  Light rays only slightly refracted
• Hyperopia


  Long sightedness

  Near objects appear blurry
• In hyperopia the lens is too thin and doesn’t refract light rays enough, causes light to focus behind the retina
• Myopia


  Shortsightedness
• Myopia


  Shortsightedness

  far away, objects appear blurry
• In myopia the lens is too thick and refracts, light rays too much, this causes light to focus on front of the retina
• To fix myopia, a concave lens is used to focus the rays into the correct place
• To fix hyperopia, a convex lens is used to correctly focus the rays