See also: Pupil (homonymy)

In the eye, the pupil is the hole located in the middle of the iris. It appears black to us since the majority of the Lumière entering inside is absorbed by fabrics of the eye. At the human ones and many animals (but at few fish species), the size of the pupil is controlled by the involuntary Contraction and the Dilatation of the iris, to control the intensity of light entering the eye. This is known under the pupillary term of Réflexe.

The shape of the pupil varies according to the species. The common forms are circular or in the shape of slit, although more complex forms can be found at watery species. The reasons of the variation of the shapes of the pupil are complex. The form approaches the characteristics Optique S, i.e., of the lens, the form, the sensitivity of the Rétine, and thus of the visual conditions of the species.

The orientation of the slit can correspond to the movements of the eye.

When an eye is photographed with a flash, the iris cannot close the pupil rather quickly and the Rétine, rich in Sang, is illuminated, causing an effect of red eyes.

Studies showed that the human ones (and especially women) are considered more attracting if their pupils large are opened, and more dilated than the normal.

Simple: Pupil (eye)