Pupil (eye)
The 'pupil' is the black opening in the centre of the eye. Light enters through the pupil and goes through the lens, which focuses the image on the retina. The size of the pupil is controlled by muscles. When more light is needed, the pupil is made larger. In brighter light, the pupil is made smaller. The pupil can be compared with the shutter of a camera. It is surrounded by the iris which is the colour part of the eye.