In the human eye, the size of the pupil is controlled by the:

1. The iris is the coloured ring around the pupil. 2. Its smooth muscles widen or narrow the pupil opening. 3. In bright light the iris contracts the pupil to admit less light. 4. In dim light the iris dilates the pupil to admit more light. 5. So the iris controls the pupil size. _Source: syllabus Science Ch 11 'Human Eye and the Colourful World'_