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AQA GCSE Biology · 8461
AQA 8461 · 4.5.2.3 The Eye Check the specification (PDF) (opens in a new tab)
Relate the structures of the eye (retina, optic nerve, sclera, cornea, iris, ciliary muscles, suspensory ligaments) to their functions.
Explain the process of accommodation for near and distant objects.
Describe myopia and hyperopia and how they are treated with lenses.
Interpret ray diagrams showing eye defects and corrections.
The eye is a sense organ: it receives information about the surroundings. Its receptors detect light intensity and colour. For you to see an object clearly, light from it must be focused onto the retina, the light-sensitive layer at the back of the eye. Retinal receptors produce electrical impulses, which travel along the optic nerve to the brain. The brain processes this information to produce vision.
Follow the route of light from the front of the eye. It first passes through the transparent cornea, which bends, or refracts, the light. Behind the cornea is the coloured iris. The opening in its centre is the pupil, through which light enters. Behind the pupil, the transparent lens changes shape to bring light into focus on the retina.
Around the lens is a ring of ciliary muscles. Suspensory ligaments connect this region to the lens. Together, the muscles and ligaments change the lens’s shape when the eye focuses on objects at different distances. Surrounding most of the eyeball is the tough white sclera, which protects it. At the back, the optic nerve leaves the eye, carrying impulses away from the retina. On a cross-section diagram, look for the cornea and iris at the front, the retina lining the inside at the back, and the optic nerve extending out behind it.
Front structures admit and focus light onto the retina; the optic nerve carries signals from the retina to the brain.
The iris controls how much light reaches the retina by changing pupil size. In dim light, the pupil dilates (widens), allowing more light in so objects are easier to see. In bright light, it constricts (narrows), allowing less light in and helping to protect the retina. This change in pupil size is an automatic reflex. It is different from changing the lens’s shape to focus on near or distant objects.
Cornea and lens refract light so it focuses on the retina. Retinal receptors detect light intensity and colour; the optic nerve carries the resulting electrical impulses to the brain.
At the front: transparent cornea, then iris with the pupil at its centre, then lens. Around the lens: ciliary muscles and suspensory ligaments, which help change lens shape. At the back: retina lining the inside and optic nerve leaving the eye. The tough outer sclera protects the eyeball.
Dim light → pupil dilates → more light enters. Bright light → pupil constricts → less light enters. The iris controls these changes.
On an eye diagram, distinguish the retina at the back of the eye from the sclera around its outside.
Describe the iris as controlling pupil size: the pupil widens in dim light and narrows in bright light.
The optic nerve carries electrical impulses to the brain; it does not carry light.
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Last updated
Retina
The light-sensitive layer at the back of the eye, containing receptors that detect light intensity and colour.
Optic nerve
The nerve that carries electrical impulses from the eye to the brain.
Sclera
The tough white outer layer that protects the eyeball.
Cornea
The transparent front part of the eye that bends incoming light.
Iris
The coloured ring of muscle that changes pupil size to control how much light enters the eye.
Pupil
The opening in the centre of the iris through which light enters the eye.
Ciliary muscles
A ring of muscles around the lens that helps change its shape for focusing.
Suspensory ligaments
Fibres connecting the lens to the surrounding ciliary muscles; changes in their tension help change the lens’s shape.
Put your knowledge into practice — try past paper questions for Biology
Retina
The light-sensitive layer at the back of the eye, containing receptors that detect light intensity and colour.
Optic nerve
The nerve that carries electrical impulses from the eye to the brain.
Sclera
The tough white outer layer that protects the eyeball.
Cornea
The transparent front part of the eye that bends incoming light.
Iris
The coloured ring of muscle that changes pupil size to control how much light enters the eye.
Pupil
The opening in the centre of the iris through which light enters the eye.
Ciliary muscles
A ring of muscles around the lens that helps change its shape for focusing.
Suspensory ligaments
Fibres connecting the lens to the surrounding ciliary muscles; changes in their tension help change the lens’s shape.