IGCSE Biology glossary
Lens
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Definition
A transparent, flexible biconvex structure in the eye that fine-focuses light onto the retina by changing shape. For near objects, the ciliary muscles contract, suspensory ligaments slacken and the lens becomes fatter (more convex). For distant objects, ciliary muscles relax, ligaments pull tight and the lens becomes thinner.
What to include in an exam answer
The process of changing lens shape is called accommodation. A very common error: ciliary muscles CONTRACT for near vision (not relax). Remember: contract = fat lens = near objects.
Example in context
Describe how the eye focuses on a near object (3 marks): The ciliary muscles contract, causing the suspensory ligaments to slacken. The lens becomes fatter (more convex) due to its elasticity. This increases the refraction of light so the image is focused on the retina.
Related syllabus topic
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