How does the eye see?

Your eye is a 24 mm camera that focuses by changing the shape of a living lens, turns light into signals with 120 million rods and 6 million cones, and even has a blind spot you never notice. The eye has about 60 dioptres of focusing power.

Read how it works: How does the eye see? · The history of understanding the eye · More boxes on Glassbox

Chapters in this interactive model

1. Inside the human eye: A ball of clear jelly with a lens at the front and a light sensor at the back.
2. How the eye focuses: A fixed cornea, a lens that changes shape, and an upside-down picture.
3. Short sight, long sight and glasses: An eyeball a millimetre too long, and the lens that fixes it.
4. The retina: rods and cones: Millions of light catchers, wired up back to front, with a hole in the middle.
5. How we see colour: Three kinds of cone, one brain doing the sums.
6. Keeping eyes healthy, and what goes wrong: Cloudy lenses, pressure on the nerve, sugar in the vessels, and too much screen.