Iris muscle

Iris (anatomy)

The iris is a thin, circular structure in the eye, responsible for controlling the diameter and size of the pupil and thus the amount of light reaching the retina.

The iris is a thin, circular structure in the eye, responsible for controlling the diameter and size of the pupil and thus the amount of light reaching the retina. The color of the iris gives the eye its color. The iris contains two groups of smooth muscles; a radial group known as dilator pupillae, and a circular group called the sphincter pupillae.

Structure

The iris consists of the following layers from back to front:

• Pigment epithelial cells: This is the most posterior layer of the iris.
• Stroma: This is the middle layer of the iris, lying between the most posterior and most anterior layers. It contains the sphincter pupillae and dilator pupillae muscles.
• Anterior border layer: This is the most anterior layer of the iris.

Function

The primary function of the iris is to control the amount of light that enters the eye. It does this by adjusting the size of the pupil, the hole at the centre of the iris through which light enters the eye.

Clinical significance

Diseases of the iris include Iritis, Aniridia, Coloboma, and Iris melanoma.

See also

• Eye
• Pupil
• Retina
• Ciliary body