GCSE Biology (AQA)

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Accommodation

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Homeostasis and Response The Human Nervous System

Accommodation

4:22 The Eye
Spec 4.5.2.3
Previous Adaptation to Dim Light Next Myopia & Hyperopia
  • Accommodation is the process of the lens changing shape to focus on near or distant objects.
  • A diagram illustrates the eye perceiving a nearby object, such as a bird.
  • To focus on near objects, the lens becomes thick; for distant objects, the lens thins.
  • The eye automatically adjusts lens thickness as a reflex to focus on surrounding objects.
  • This adjustment is termed accommodation, aiding in viewing objects at varying distances.
  • Light entering the lens at an angle changes direction, similar to cars moving from pavement to sand.
  • This bending of light is called refraction, which helps focus light on the retina.
  • The cornea consistently refracts light into the pupil, while the lens adjusts its shape to further focus light onto the retina.
  • Objects appear in focus when light waves converge on the retina; otherwise, they appear blurry.
  • Near objects require the lens to be thicker to refract light more due to the wider angle of incoming light, aiding in convergence on the retina.
  • Far objects, with nearly parallel light waves by the time they reach the eye, require less refraction.
  • Lens shape is controlled by ciliary muscles and suspensory ligaments.
  • When viewing distant objects, suspensory ligaments are tight, and ciliary muscles are relaxed, resulting in a thin lens.
  • Conversely, for near objects, suspensory ligaments are loose, and ciliary muscles are contracted, resulting in a thicker lens.
  • A table summarizes the changes: for near objects, ciliary muscles contract, suspensory ligaments loosen, and the lens is thick; for far objects, ciliary muscles relax, suspensory ligaments tighten, and the lens is thin.
  • Proper vocabulary is crucial: ligaments tighten (not contract) and muscles relax (not loosen).

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