Iris - GCSE Biology Definition

The iris is the coloured part of your eye that surrounds the black pupil in the centre. It controls the amount of light that enters your eye by changing the size of the pupil. In bright light, the iris makes the pupil smaller to let in less light; in dim light, it makes the pupil bigger to let in more light. This helps protect the sensitive inner parts of your eye and improves your vision. The iris is important for maintaining the right amount of light entering your eye, helping you to see clearly in different lighting conditions.