Erin Norriss, of Ilam Primary School, asks :-

How do we see?

Kenneth Tarr, an ophthalmologist, responded.

When you look at something, say a lemon, what your eyes are receiving is light reflected from the lemon. That's why you can't see in the dark as there is no light to be reflected.

The light reflected off the lemon comes into your eyes through the black pupil, being partly focussed as it passes through the curved surface of your eyeball. Behind the pupil is a lens which completes the focusing of the light onto the retina at the back of your eyeball. The lens's shape can be changed by small muscles, allowing you to focus on things near or far away. The image projected on to the retina by the lens is actually upside-down: the brain turns it the other way up later on.

The retina is covered with light sensitive cells called rods and cones which convert the image into electrical signals which are passed up through the optic nerve to the region at the back of your brain that deals with visual images, changing them into messages that the rest of the brain can use.

The way that we see is very complex, especially the way the brain deals with images. For example, with the lemon different areas of the brain would analyze its shape, colour, size, how far away it is and if it is moving. So as you can see, even an action as simple as looking at a lemon starts a complex chain of events in your eyes and brain that leads to the amazing experience of sight.