This section contains definitions of some of the functions the eye can perform, without attempting to provide too much detail. Superficially the eye resembles a camera in so far that it has a lens, which throws an image onto the light sensitive back surface, which is called the retina. Focussing is not achieved by altering the distance between lens and retina (as with a camera) but by changing the shape of the lens. In the retina there are two types of receptor, rods, which are highly light-sensitive and are principally responsible for detection of shape and movement, and cones, which are less sensitive to light, but can distinguish colours.
