Nervous system
Eye
The eye is the organ of sight. It focuses light onto a light-sensitive layer at the back (the retina), which turns it into nerve signals the brain interprets as images.
What it is
The eye is a fluid-filled ball about 2.5 cm across, with a clear front (cornea and lens) that focuses light and a light-sensing lining (retina) at the back.
Where it is
In the bony eye socket of the skull, cushioned by fat and moved by small muscles.
What it does
Detects light and enables vision — focusing images, adjusting to brightness, and sending visual information to the brain.
How it works
Light passes through the cornea and lens, which focus it onto the retina. The retina's cells convert light into electrical signals sent along the optic nerve to the brain, which builds them into the images we see.
When things go wrong
Common conditions affecting the eye
- Short- and long-sightedness (refractive errors)
- Cataracts
- Glaucoma
- Age-related macular degeneration
- Conjunctivitis
Education and reference only. This explains the anatomy in plain terms and is not a diagnosis. Sudden severe symptoms — such as severe chest pain, breathlessness or collapse — are an emergency; call 999.
Looking after it
Keeping your eye healthy
Regular eye tests, protecting eyes from strong sun, not smoking, managing diabetes and blood pressure, and getting sudden vision changes checked urgently all protect sight.
Did you know?
An interesting fact
The eye can distinguish an estimated ten million colours and adjusts to a huge range of light levels automatically.
Answers
Eye: frequently asked questions
How does the eye work?
Light is focused by the cornea and lens onto the retina at the back of the eye, which converts it into nerve signals the brain interprets as images.
When is sudden vision loss an emergency?
Sudden loss of vision, a curtain across your sight, or a painful red eye with blurred vision needs urgent (same-day) eye assessment, as some causes threaten sight.
The nervous system
Related organs
Sources
Where this is drawn from
- NHS — Anatomy and body systems
- Gray's Anatomy for Students
- TeachMeAnatomy / TeachMePhysiology
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