What happens to the pupil not exposed light?

When one pupil is not exposed to light, the pupil will dilate (become larger) in order to allow more light to enter the eye. This is a natural response of the eye to low light conditions. The pupil is controlled by the iris, which is a muscle that surrounds the pupil. When the iris contracts, the pupil becomes smaller; when the iris relaxes, the pupil becomes larger.

The dilation of the pupil when one eye is not exposed to light is a reflex that is controlled by the brain. This reflex is called the pupillary light reflex. The pupillary light reflex helps to ensure that both eyes receive the same amount of light, which is important for maintaining clear vision.