The eye

• what stimuli are the receptors of the eye sensitive to?

  light intensity and colour
• 2 main functions of structures found within the eye

  • focusing on near or distant objections - accommodation
  • adaptation to dim light
• Describe the structure and function of the retina

  light-sensitive layer found at the back of eye

  light stimulates the retinal cells, resulting in impulses being sent to the brain
• Describe the structure and function of the optic nerve

  connects the eye and the brain

  carries impulses to the brain so that an image can be visualised
• Describe the structure and function of the sclera

  tough outer layer of the eye which protects its internal structures
• describe the structure and function of the cornea


  curved transparent layer at the front of the eye

  lets light into the eye and allows light to be focused onto the retina
• describe the structure and function of the iris

  muscle which controls the size of the pupil by contracting or relaxing

  allows the eye to adjust to bright or dim lighting
• describe the structure and function of the ciliary muscles and suspensory ligaments

  hold the lens in place and control its shape
• describe how the iris alters the size of the pupil in bright and dim light

  • in bright light: circular muscles contract and radial muscles relax - makes pupil smaller to avoid retinal damage
  • in dim light: circular muscles relax and radial muscles contract - makes pupil larger so more light can enter the eye
• What is accommodation?

  alteration of the lens shape in order to focus on near or distant objects
• How does the eye focus on a nearby object?

  • ciliary muscles contract
  • suspensory ligaments loosen
  • lens becomes thicker and more curved - light rays are refracted strongly
• how does the eye focus on a far away object

  • ciliary muscles relax
  • suspensory ligaments tighten
  • lens becomes thinner - light rays are refracted weakly
• What is myopia

  • short-sightedness - usually occurs when the lens of the eye is too curved
  • light is focused in front of the retina so images appear blurry
• how can myopia be treated?

  glasses with a concave lense which spreads out light rays so they can be focused on the retina
• What is hyperopia?

  • long-sightedness - occurs when the lens of the eye is too flat
  • light is focused behind the retina so images appear out of focus
• how can hyperopia be treated?

  glasses with a convex lense which brings the light rays together so they can be focused on the retina
• Two types of contact lenses

  • hard - rigid material, last a long time, must be kept sterile
  • soft - flexible material, last for a shorter time, more comfortable
• What is laser eye surgery?

  • use of lasers to fix visual defects in adults
  • myopia - lasers reduce the thickness of the cornea so light is refracted less strongly
  • hyperopia - lasers alter the curvature of the cornea so that light is refracted correctly
• how can replacement lenses be used to treat visual defects?

  can be implanted into the eye (along with natural lens) or it may replace the natural lens altogether
• risks of lens replacement

  retinal damage, cataracts and infections