The Eye

• Parts of the eye

  A) Sclera

  B) Retina

  C) Fovea

  D) Optic nerve

  E) Lens

  F) Cilirary muscle

  G) Pupil

  H) Iris

  I) Cornea

  J) Suspensory Ligament

  
• Ciliary muscle pulls the suspensory ligaments to change the shape of the lens to help focusing
• Cornea refracts light into the eye and is transparent, to begin focusing
• Lens focuses light onto the retina
• Optic nerve carries impulses to the brain
• Pupil lets light through to the lens
• Retina is a light sensitive layer, which sends signals to the optic nerve
• Suspensory ligaments hold the lens in place
• The eye focuses light on the retina by changing the shape of the lens, this is known as accomodation
• Near objects

  • The ciliary muscles contract, which slackens the suspensory ligaments
  • The lens becomes more curved
  • This increases the ammount by which it refracts ligjt
• Distant objects

  • The ciliary muscles contract which allows the suspensory ligaments to pull tight
  • This makes the lens thin and less curved
  • It refracts light by a smaller ammount
• Too much light can damage the light sensitive cells
• Not enough light means there is not enough stimulus cells
• Long-sighted (Hyperopia)

  • People are unable to focus on near objects
  • This occurs when the lens is the wrong shape and doesn't refract the light enough or the eyeball is too short
  • The images of near objects are brought into focus behind the retina
  • This can be solved with glasses that have a convex lense
• Short-sighted (myopia)

  • Unable to focus on distant objects
  • The lens is in the wrong shape, refracts light too much or the eyeball is too long
  • Images are brought into focus infront of the retina
  • Glasses with a concave lens can be used to correct it
• Light Conditions

  • Circular muscle is contracted
  • Radial is relaxed
• Dark conditions

  • Circular muscle is relaxed
  • Radial muscle is contracted
• In dark conditions, the pupil is large (radial) to maximise the light being let in
• In light conditions the pupil is smaller to reduce the light being let in to prevent damage to the retina
• Objects with a near position

  • Ciliary muscles contract
  • Suspensory ligaments are slacked and loose
  • Low muscle tension
  • Lens is fat
  • Light is strongly refracted
• Objects with a distant position

  • Ciliary muscles relax
  • Suspensory ligaments are tightened
  • High muscle tension
  • Lens is thin
  • Light is weakly refracted