The iris controls the amount of light entering the eyes.The iris
automatically adjusts the size of the pupil according to the intensity
of light received by the eye.If the amount of light received by the eye
is large,then the iris contracts the pupil (makes the pupil small) and
reduces the amount of light entering the eye.On the other hand,if the
amount of light received by the eye is small(as in a dark room or during
night),the iris expands the pupil(makes the pupil large) so that more
light may enter the eyes.Thus,the iris regulates the amount of light
entering the eye by changing the size of the pupil. |