The stroma of the iris is a fibrovascular layer of tissue located at the front of the iris.

Structure

The stroma is a delicate interlacement of fibres. Some circle the circumference of the iris and the majority radiate toward the pupil.

Blood vessel Blood vessels are the tubular structures of a circulatory system that transport blood throughout many Animal, animals’ bodies. Blood vessels transport blood cells, nutrients, and oxygen to most of the Tissue (biology), tissues of a Body (bi ...

s and

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons). Nerves have historically been considered the basic units of the peripheral nervous system. A nerve provides a common pathway for the Electrochemistry, electrochemical nerv ...

s intersperse this mesh. In dark eyes, the stroma often contains

pigment A pigment is a powder used to add or alter color or change visual appearance. Pigments are completely or nearly solubility, insoluble and reactivity (chemistry), chemically unreactive in water or another medium; in contrast, dyes are colored sub ...

granules. Blue eyes and the eyes of albinos, however, lack pigment. Iris structure

The stroma connects to a

sphincter A sphincter is a circular muscle that normally maintains constriction of a natural body passage or orifice and relaxes as required by normal physiological functioning. Sphincters are found in many animals. There are over 60 types in the human bo ...

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. The back surface is covered by a commonly, heavily pigmented epithelial layer that is two cells thick (the iris pigment epithelium), but the front surface has no epithelium. This anterior surface projects as the muscles dilate.

References

External links

* Human iris {{eye-stub