Iris (anatomy)

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 color of the iris gives the eye its color.

Structure

The iris consists of two main layers: the front pigmented fibrovascular known as a stroma and, beneath the stroma, pigmented epithelial cells.

Stroma

The stroma connects to a sphincter muscle (sphincter pupillae), which contracts the pupil in a circular motion, and a set of dilator muscles (dilator pupillae) which pull the iris radially to enlarge the pupil, pulling it in folds.

Pigmented epithelial cells

The pigmented epithelial cells, lying behind the stroma, are a double layer of columnar cells that secrete and absorb aqueous humor.

Function

The main function of the iris is to control the amount of light getting into the eye. This is done by adjusting the size of the pupil, which is the hole in the middle of the iris through which light enters the eye.

Clinical significance

Diseases such as aniridia, coloboma, and iritis can affect the iris.

See also

• Eye color
• Human eye

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