Pupil

Pupilla

Sensory (eye & ear)OrgansHeadLeft and right

View left in 3D View right in 3D

What it is

The round opening in the centre of the iris. It looks black because light entering it is absorbed inside the eye.

Function

Admits light to the lens and retina; its size adjusts to brightness, focusing distance and emotion.

Size

2-4 mm in daylight, up to 8 mm in darkness; shown here at 4 mm.

Clinical note

Unequal or unreactive pupils are an urgent neurological sign (e.g. a third-nerve palsy from raised intracranial pressure).