Eye

• Optic nerve


  Originates in an area of the retina called the optic disc, where there are no photoreceptors. This part of the retina is commonly known as the blind spot.
• Light passing through the eye to the retina


  Light is refracted (bent) by the cornea and lens, so that the light is brought to a focus on the retina.
• Brain


  Interprets the inverted image the right way up.
• Photoreceptors


  Rod cells work well in dim light but can only see black and white. Cone cells only work in bright light.
• Types of cone cells


  • Red
  • Green
  • Blue
• Accommodation


  1. Ciliary muscle

  2. Suspensory ligaments

  3. Lens shape
• In bright light


  The circular muscles contract and the radial muscles relax, so the pupil is constricted. This helps to reduce the amount of light entering the eye to avoid damage to the retina.
• In dim light


  The circular muscles relax and the radial muscles contract, so the pupil is dilated. This allows as much light as possible to fall on the retina to maximise vision.