A patient is diagnosed with a cataract in one eye. Explain how a cataract affects vision and describe how this condition can be treated.

WJEC A-Level Biology (Wales) — 4.6 The nervous system · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

A cataract is a condition that develops slowly and becomes more common as people age.

Model answer (5 marks)

A cataract causes the lens to become cloudy due to a build‑up of protein. The cloudy lens restricts the amount of light that reaches the retina, producing blurred or reduced vision. Treatment is surgical removal of the cloudy lens, replacement with an artificial intra‑ocular lens or, less commonly, laser eye surgery to clear the cataract.

Examiner tips

Use the exact terms ‘cloudy lens’, ‘protein build‑up’, ‘restricted light’, ‘blurred vision’, and ‘surgical removal/replacement’
Show the cause–effect chain: protein → cloudiness → less light → blurred vision
Mention the main treatment option (surgery) and note the alternative (laser)

Common mistakes

Confusing cataract with other eye conditions such as glaucoma
Failing to explain the protein build‑up or the light restriction
Omitting the surgical treatment or using vague terms like ‘treatment’ without detail

Mark scheme (5 marks)

A cataract causes the lens to become cloudy
This is due to a build-up of protein in the lens
The cloudy lens restricts / reduces the amount of light passing through to the retina
This results in reduced / blurred / restricted vision
Treatment involves surgical removal of the cloudy lens / replacement of the lens / laser eye surgery to remove the cataract

Key terms in this question

cataract