Human eye with blue iris

Photomacrograph of a close-up view of the pupil and iris in a human eye. The human eye is a complex organ and works in a similar way to a camera. Light enters the eye through the pupil (black). The size of the pupil is controlled by the iris (blue) in order to adjust how much light enters the eye at any given time. Here, the iris is coloured blue, but other colours such as brown, hazel, green and grey can be present instead. Light enters the eye and is focused onto the retina at the back of the eye, which then converts these images into electrical signals and sends them on to the brain to interpret and make sense of. Width of image is 2 cm.