The Eye: Structure, Function and Focusing — AQA GCSE Biology (Separate)

The eye focuses light from objects at different distances onto the retina. This adjustment is called accommodation.

Accommodation

Accommodation is the process of changing the shape of the lens to focus on near or distant objects. It is controlled by the ciliary muscles and suspensory ligaments.

Focusing on a near object

• The ciliary muscles contract.
• The suspensory ligaments loosen (slacken).
• The lens becomes thicker (more rounded) and refracts light strongly.

Focusing on a distant object

• The ciliary muscles relax.
• The suspensory ligaments tighten (pull tight).
• The lens is pulled thin (flatter) and refracts light less.

The retina and pupil reflex

Light is focused onto the retina, which contains receptors sensitive to light intensity and colour. The iris controls the pupil size: in bright light the pupil constricts (gets smaller) to protect the retina; in dim light it dilates (gets bigger) to let more light in. This is a reflex.

Exam tips

• Define accommodation as changing the lens shape to focus.
• Near object → ciliary muscles contract, ligaments slacken, lens thick/rounded.
• Distant object → ciliary muscles relax, ligaments tight, lens thin/flat.
• The pupil reflex adjusts light entering the eye.