Iris

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

Beneath the stroma, pigmented epithelial cells, which are two cells thick, are in contact with the long ciliary nerves that are part of the suspensory ligaments of the lens.

Function

The main function of the iris is to control the amount of light getting into the eye. To do this, it uses the dilator pupillae muscles to widen the pupil and the sphincter pupillae muscles to constrict it.

Clinical significance

Diseases such as aniridia, coloboma and iris heterochromia can affect the iris. Iridology is an alternative medicine technique that claims that patterns, colors, and other characteristics of the iris can be examined to determine information about a patient's systemic health.

See also

• Eye color
• Human eye

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