Topic Summaries

Accommodation and adaptation to dim light

GCSE > Biology > AQA > GCSE Biology Topic Summaries > The brain and the eye > Accommodation and adaptation to dim light
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Science skills: Measuring results

  • Accommodation is the automatic process of changing the shape of the lens to focus on near or distant objects.
  • To focus on a near object:
    • The ciliary muscles contract
    • The suspensory ligaments loosen
    • The lens becomes shorter and thicker, refracting light rays strongly
  • To focus on a distant object:
    • The ciliary muscles relax
    • The suspensory ligaments are pulled tight
    • The lens is pulled thinner/longer and only slightly refracts light
  • When light intensity is low (e.g. at night) the pupil becomes larger (dilates) in a reflex response to maximise the amount of light entering the eye. The muscles in the iris increase the size of the pupil (dilated pupils), radial muscles contract, and circular muscles relax. The opposite takes place in bright light, to prevent too much light from entering and damaging the eye.

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