As you walk into a brightly lit room, the black structure in the center of your eye seems to shrink to a tiny black dot. This response is caused by the action of the eye structure called the:

iris

Explanation:

Iris: Iris is a structure that is being found in birds, human beings, and mammals and is described as a circular as well as thin structure which is being found in the eye and therefore it is responsible for controlling the pupil's size, diameter, and amount of light which is entering the retina of an eye. An organism's eye color is generally being determined by the iris of the eye.

Iris is made up of pigments, connective tissues, and smooth muscle fibers.

In the question above, the given statement signifies the "iris".

answer; to save lives and protect property;