How the Eye Works

You can think of the eye as a miniature camera - it has a camera body (the eyeball), a lens to focus the light (the cornea at the front of the eye together with a small lens inside the eye) and a light sensitive film at the back (the retina). The main function of the eye is to focus the light arriving at the front into a clear image on the retina at the back.

A Camera and Your Eye

a) camera	b) human eye

Most of this focusing is done by the cornea, the clear window through which you can see the colour of the iris (your "eye colour", be it blue, green, brown or black). Two-thirds of the focusing is actually done by the cornea, which needs a healthy tear film over it to make the surface perfectly smooth. The partially focused light now passes through the hole in the middle of your iris (your pupil) and now arrives at the lens sitting right next door. The lens does the final third of the work, but has the important job of changing its shape to provide a variable focus. This means that light from both far and near can be in focus on your retina (in the same way that you have to turn the lens ring on bigger cameras to bring objects into a sharp image). The light continues on its journey through the middle part of the eye, which is filled with a clear jelly, before arriving at its destination - the retina.

The Different Parts of Your Eye

Iris
The iris is the coloured part of your eye, and is like the metal diaphragm in your camera. See the figure below. It canand close, changing the size of the central hole, which is your pupil. The iris contains tiny muscles to constrict and close your pupil, and another set laid out like spokes in a wheel, which contract and the pupil wide when the light around is dim.

a) camera diaphragm	b) human iris

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