Iris (anatomy)
Iris (anatomy)
The Iris (pronounced /ˈaɪrɪs/) 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.
Etymology
The term "iris" is derived from the Greek word for rainbow, which is also "iris" (ἶρις), due to the many colors the iris can have.
Structure
The iris consists of two main layers: the front pigmented fibrovascular known as a stroma and, beneath the stroma, pigmented epithelial cells. 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.
Function
The primary 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 in dim light conditions, and the sphincter pupillae to constrict the pupil in bright light.
Related Terms
- Pupil: The black circular opening in the iris that lets light in.
- Retina: The light-sensitive layer of tissue at the back of the inner eye.
- Stroma of iris: The front pigmented fibrovascular tissue.
- Sphincter pupillae: The muscle in the iris that contracts the pupil.
- Dilator pupillae: The muscle in the iris that enlarges the pupil.
External links
- Medical encyclopedia article on Iris (anatomy)
- Wikipedia's article - Iris (anatomy)
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