The eye: structures and their functionsSpec 4.5.2.3
In short
The eye is a sense organ containing receptors sensitive to light intensity and colour, found in the retina. The cornea refracts light, the iris controls the size of the pupil, and the optic nerve carries impulses to the brain. In dim light the pupil gets wider so more light enters; in bright light it gets narrower, which protects the retina.
The eye is a sense organ containing receptors sensitive to light intensity and colour.
| Structure | How its structure relates to its function |
|---|---|
| Retina | Contains the light receptors. It is where the image is focused and it detects light intensity and colour |
| Optic nerve | Carries impulses from the receptors in the retina to the brain |
| Sclera | The tough white outer layer. It protects the eye and keeps its shape |
| Cornea | Transparent front surface. It lets light in and refracts (bends) the light rays |
| Iris | Muscles that control the size of the pupil and so how much light enters the eye |
| Ciliary muscles | A ring of muscle around the lens that contracts or relaxes to change the lens shape |
| Suspensory ligaments | Hold the lens in place and connect it to the ciliary muscles. Their tension changes the lens shape |
(opens full size in a new tab)Adaptation to dim light
The iris controls how much light reaches the retina. In dim light the pupil gets wider so more light enters. In bright light the pupil gets narrower so less light enters, which protects the retina.
Link each structure to its job with a reason, for example ‘the cornea refracts light’, not just ‘the cornea is at the front’.
Written and checked against the AQA GCSE Biology (8461) specification · Updated October 2026