Dilation and constriction of the pupil are controlled by the

Iris controls the dilation and constriction of the pupil

Explanation:

Iris is the part of the eye which is involved in controlling of the working mechanism of the pupil. It is a thin membrane which surrounds pupil. The specialized muscle present in Iris region of the eye are involved in controlling of light entry and its effect on the pupil.

When the light entering the eyes are very bright, it makes the iris to constrict and which in turn causes the pupil to constrict, whereas when the light entering the eyes is very dim, the iris dilates and causes pupil to dilate.