The Eye

• Eye


  A sense organ
• Eye


  • There's a lot to get your head around
  • Get focused
• Parts of the eye

  • Sclera
  • Cornea
  • Iris
  • Pupil
  • Lens
  • Retina
  • Ciliary muscles
  • Suspensory ligaments
  • Optic nerve
• Sclera


  The tough, supporting wall of the eye
• Cornea


  • The transparent outer layer found at the front of the eye
  • It refracts (bends) light into the eye
• Iris


  Contains muscles that allow it to control the diameter of the pupil (the hole in the middle) and therefore how much light enters the eye
• Lens


  Focuses the light onto the retina (which contains receptor cells sensitive to light intensity and colour)
• Ciliary muscles and suspensory ligaments

  Control the shape of the lens
• Optic nerve


  Carries impulses from the receptors on the retina to the brain
• Iris reflex - adjusting for bright light

  1. Light receptors in the eye detect very bright light

  2. Reflex is triggered to make the pupil smaller

  3. Circular muscles in the iris contract and radial muscles relax

  4. This reduces the amount of light that can enter the eye

  5. Opposite process happens in dim light
• Focusing on near and distant objects

  1. To look at near objects: Ciliary muscles tighten, suspensory ligaments relax, lens becomes fatter (more curved)

  2. To look at distant objects: Ciliary muscles relax, suspensory ligaments tighten, lens becomes thinner (less curved)
• Long-sightedness (hyperopia)


  • Lens is the wrong shape and doesn't refract light enough, or eyeball is too short
  • Images of near objects are brought into focus behind the retina
  • Can be corrected with convex glasses lens
• Short-sightedness (myopia)


  • Lens is the wrong shape and refracts light too much, or eyeball is too long
  • Images of distant objects are brought into focus in front of the retina
  • Can be corrected with concave glasses lens
• Treatments for vision defects

  • Wearing glasses
  • Contact lenses
  • Laser eye surgery
  • Replacement lens surgery
• Contact lenses


  • Thin lenses that sit on the surface of the eye and are shaped to compensate for the fault in focusing
  • Lightweight and almost invisible
  • More convenient than glasses for activities like sports
  • Two main types: hard lenses and soft lenses
• Laser eye surgery


  • Laser can be used to vaporise tissue, changing the shape of the cornea to improve short or long sight
  • Surgeon can precisely control how much tissue the laser takes off to completely correct the vision
  • Risk of complications such as infection or the eye reacting in a way that makes vision worse
• Replacement lens surgery


  • Natural lens of the eye is removed and an artificial lens, made of clear plastic, is inserted in its place
  • Involves work inside the eye, so carries higher risks than laser eye surgery, including possible damage to the retina