Pupil

The pupil is a hole located in the center of the iris of the eye that allows light to strike the retina. It appears black because light rays entering the pupil are either absorbed by the tissues inside the eye directly, or absorbed after diffuse reflections within the eye that mostly miss exiting the pupil.

Function

The main function of the pupil is to regulate the amount of light that gets into the eye. When the environment is bright, the iris contracts, reducing the size of the pupil (miosis) to limit the amount of light that enters. In dim conditions, the iris relaxes and the pupil dilates (mydriasis) to allow more light to reach the retina.

Anatomy

The pupil is an opening that is located in the center of the iris. The size of the pupil is controlled by two muscles: the sphincter pupillae and the dilator pupillae. The sphincter pupillae is a circular muscle that constricts the pupil in bright light, while the dilator pupillae is a radial muscle that dilates the pupil in low light.

Clinical significance

Changes in the size, shape, or reactivity of the pupils can be indicative of various medical conditions. For example, anisocoria is a condition characterized by unequal pupil sizes. It can be a normal variant, or it can be a sign of a medical emergency, such as a brain aneurysm. Other conditions that can affect the pupils include Horner's syndrome, Adie's pupil, and Argyll Robertson pupil.

See also

• Iris (eye)
• Retina
• Anisocoria
• Horner's syndrome
• Adie's pupil
• Argyll Robertson pupil

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