the eye

• what is the purpose of the optic nerve?

  carries electric impulses from the receptors to the brain
• what is the purpose of the lens?

  refracts light, focusing it on the retina
• what is the purpose of the cornea?

  refracts light into the eye
• what causes long/short sightedness?

  long: lens doesn’t bend light enough/eyeball is too short

  short: lens bends light too much/eyeball is too long
• what can correct long/short sightedness?

  glasses/contact lenses with a concave lens
• what is the purpose of the light receptor?

  (in the eye) detect very bright light and send a message along a sensory neurone to the brain
• when is the pupil made smaller?

  when a message travels along a relay neurone to a motor neurone which tells circular muscles in the iris to contract, making the pupil smaller
• what is the purpose of the iris?

  controls how much light enters the pupil
• what is the purpose of the retina?

  light sensitive and covered in receptor cells called rods and codes which detect light
• what are the purposes of the rods and cones?

  rods: sensitive in dim light, can’t sense colour

  cones: sensitive to different colours, can’t sense dim light
• what type of lens can fix long-sightedness?

  convex lens
• what type of lens can fix short-sightedness?

  concave lens
• what causes red-green colour blindness?

  when red or green cones in the retina aren’t working properly. There’s no cure for colour blindness as cone cells can’t be replaced
• what is a cataract?

  a cloudy patch on the lens which stops light from being able to enter the eye normally, usually causing blurry vision, it can be treated by using an artificial lens
• how can brain tumours be treated?

  chemotherapy, radiotherapy or brain surgery.
• what is the cornea?

  the transparent frontal portion of the eye responsible for refracting light.
• what is the pupil?

  a hole in the centre of the iris, through which light passes through to get to the retina.
• what are suspensory ligaments?

  a ring of fibres that connect ciliary muscles to the lens.
• what are ciliary muscles?

  a ring of smooth muscle that can change the shape of the lens, which the eye uses to focus light.
• what is the iris?

  controls pupil diameter, and the quantity of light reaching the retina.
• what happens to the eye when focusing on a close object?

  the ciliary muscles contract and the suspensory ligaments loosen. The lens becomes thicker and rounder, resulting in significant refraction of light rays.
• what happens to the eye when focusing on a distant object?

  the ciliary muscles relax and the suspensory ligaments tighten. The lens becomes flatter and thinner, resulting in minor refraction of light rays.
• rays focus in front of the retina

  short-sightedness
• rays focus behind the retina

  long-sightedness