Pupil Picture

The pupil is the hole in the middle of the iris. It appears black because most of the
light entering it is absorbed by the tissues inside the eye. In humans and many animals
(but few fish), the size of the pupil is controlled by involuntary contraction and
dilation of the iris, in order to regulate the intensity of light entering the eye. This
is known as the papillary reflex. The pupil is shown 3 layers in on the
front of the eye in the picture.

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