The Function of the Pupil

There are muscles in your eyes responsible for changing the diameter of the pupil. The eye has to adjust the size of the hole to help control light exposure and to focus the image. What causes the expansion or contraction of the pupil is actually the set of muscles within the iris. This is what your iris is for. And so here's a wonderful anatomy fact that every one should know: Your pupils change their size to optimize vision for a particular situation.