How do our eyes work?

by Zoë Gamble


CC-BY science made simple


Many of us take our vision for granted, but have you ever wondered how this fascinating organ actually works? How do our eyes allow us to see objects as small as a human hair, or as far away as the Andromeda Galaxy (2.6 million light years)?

Light enters our eyesHow our pupils react to light

Light from the sun, or an artificial light, travels in a straight line, bounces off objects and into our eyes through the pupil. Depending on the amount of light, the iris changes the size of the pupil to let more or less light in. This is to prevent damage to the eyes, by stopping too much light entering the eye when it is bright, and maximising the amount of light entering the eye when it’s dark.

Diagram of the human eye: CC-BY Holly Fischer


The light is focussed

The light then passes though the lens. The lens focuses the light onto the back surface of the eye, the retina. Depending on how far away the object is, our lens needs to change shape to keep the light focussed on the retina.

How the lens focusses light: Public domain Scott Foresman

A fatter lens bends light more than a flatter lens. The human eye changes the shape of the lens as we look at far or near objects to keep them in focus. This is called accommodation. When we look at a far object, the light does not need to bend a lot to converge on the retina, so the suspensory ligaments pull on the lens to make it flat. When we look at a near object, the light has to bend more to converge on the retina, so the suspensory ligaments pull less, allowing the lens to spring back into a fatter shape,

 When things go wrong

For many people, light from an image is not perfectly focussed on their retina. Depending on the severity of the deviance, this can lead to a person needing to wear glasses. A short-sighted person can see things close-up, but has trouble seeing things further away. A long-sighted person struggles to see near objects, but can see distant objects.



Correcting vision – Stuart Fox CC-BY-SA

Image A shows how the light is focussed in a hyperopic eye, or a long-sighted eye. The lens does not cause the light to bend enough, leading to the focal point being beyond the retina. To rectify this, a long-sighted person can wear glasses with a convex lens (image B) This causes the light to bend more, and converge on the retina. The opposite is true for a short-sighted person. Image C shows how the lens in a myopic eye focuses the light too much, causing the focal point to be in front of the retina. This can be corrected with a concave lens, which causes the light to spread, and so converge on the retina. Do you wear glasses?

The light is turned into an electrical impulse

After receiving focussed light, the retina transforms this into an electrical impulse, which travels to the brain via the optic nerve. The image we receive on the retina is actually upside-down – our brains turn the image around so we don’t get confused!

Things to do:

Find out whether you are right- or left- eyed

10 things to do with your eyes closed

Try out this interactive guide to the human eye, which was made by Vision Direct who were inspired by this blog!

Zoom into the eye and find out more about the different parts with this fun tool from Lenstore

Curriculum links


KS2 – Light
  • recognise that light appears to travel in straight lines
  • use the idea that light travels in straight lines to explain that objects are seen because they give out or reflect light into the eye
  • explain that we see things because light travels from light sources to our eyes or from light sources to objects and then to our eyes
KS3 – Light Waves
  • use of ray model to explain imaging in mirrors, the pinhole camera, the refraction of light and action of convex lens in focusing (qualitative); the human eye


  • how light travels and how this can be used


SCN 3-11a
  • By exploring the refraction of light when passed through different materials, lenses and prisms, I can explain how light can be used in a variety of applications.

Northern Ireland

KS3  – Forces and energy
  • Sound and light


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Posted in Biology, Physics
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