How We See
Of all the senses, we rely most on that of sight, or vision. Our eyes tell us most about the world we live in.
But what is sight ? To see something you need eyes, but you also need a brain. Light from the outside enters your eyes, which then sends a message about the light to your brain. These messages are carried from the eye to the brain by the optic nerves.
As with your other senses, it is really your brain that recognizes the nerve messages that know what you are looking at. Without your brain, your eyes would be like cameras taking photographs without anyone being there to look at them.
How the eye works.
In some ways, the human eye does resemble a small ball shaped camera. It fits into the eye socket of the skull, where six small muscles are used to swivel it. At the front of the eyes is a transparent lens, through which the light passes. The lens bends light rays so that they focus at the back of the eye on a layer called the retina. This layer is rather like photographic film in a camera. When light from an object is focused on it, it forms an image of the object.
However, unlike a photograph, the image on the retina is only a temporary one. You can only test this. If you stare at a bright light, such as from a lamp, then close your eyes, you see at first a bright colored image. This retina image soon fades. Because, the retina quickly returns to normal, it can soon form another image. In this way, you can see one thing after another.
In the retina are special cells, which are sensitive to light. These are the cells which form images and which passes the messages to the optic nerves and the brain. These cells are of two kinds called rods and cones.
Rods are sensitive on to the amounts of light or its intensity. They enable us to see black, grey, and white. Cones are sensitive to colored light and enable us to see colors.. You may notice how colors seem to disappear as light fades in the evening. This is because rods are more sensitive that cones son in dim light you can only see in black and different shades of grey.
The pupil is a hole formed by the iris, not unlike a camera lens. The iris opens in dim light to make the pupil bigger to let in more light: in bright light the iris contracts to make a smaller pupil.