What is the function of the iris and the muscles connected to the lens in the human eye ?

Explanation

When the incident light is very bright, the muscles of the iris stretch to reduce the size of the pupil. When the incident light is dim, the muscles of the iris relax to increases the size of the pupil. Thus, the iris controls the size of the pupil and thereby regulates the amount of light entering the eye.
When a distant object is to be observed , the ciliary muscles relax so that the eye lens becomes flat. This increases the focal lenght of the lens. Therefore , a sharp image of the distant object is formed on the retina.
Thus, we can see a distant object clearly.

When an object closer to the eye is to be observed, the ciliary muscles contract increasing the curvature of the eye lens . The eye lens , therefore, becomes rounded. This decreases the focal length of the lens. Therefore, a sharp image of the nearby object is formed on the retina . Thus, we can see a nearby object clearly