The iris is the colored part of the eye. A circular muscle in the
iris controls the amount of light entering the eye through the pupil, the black
area in the center of the iris.
The lens is located behind the iris and is normally clear. Light
passes through the pupil to the lens. Small muscles attached to the lens can
change its shape. Tightening or relaxing these muscles causes the lens to
change shape, allowing the eyes to focus on near or far objects
(accommodation).
