The main function of the pupil is to allow a central light ray to pass through the iris and illuminate the fovea of the retina, where most of the eye's photoreceptors are concentrated. The size of the pupil varies depending on the amount of light in the environment. Disorders of the pupil include:
- Anisocoria - pupils of unequal size
- Abnormal shape of pupils
- Abnormal pupillary reaction to light
The pupillary size is mediated by the sympathetic and parasympathetic nervous systems. The former controls pupillary dilation while the latter mediates pupillary constriction.
The iris has two muscles that modulate the size of the pupil: the dilator muscle which produces mydriasis under sympathetic innervation, and the sphincter muscle which produces miosis under parasympathetic innervation.
