Just in front of the root of the iris is the region referred to as the trabecular meshwork, through which the aqueous humour constantly drains out of the eye, with the result that diseases of the iris often have important effects on intraocular pressure and indirectly on vision. The iris and ciliary body together are known as the anterior uvea. The outer edge of the iris, known as the root, is attached to the sclera and the anterior ciliary body. The high pigment content blocks light from passing through the iris to the retina, restricting it to the pupil. This anterior surface projects as the dilator muscles. The back surface is covered by a heavily pigmented epithelial layer that is two cells thick (the iris pigment epithelium), but the front surface has no epithelium. The constricting muscle is located on the inner border. The outer border of the iris does not change size. The pupil's diameter, and thus the inner border of the iris, changes size when constricting or dilating. The sphincter pupillae is the opposing muscle of the dilator pupillae. The stroma is connected 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. The iris consists of two layers: the front pigmented fibrovascular layer known as a stroma and, beneath the stroma, pigmented epithelial cells. In optical terms, the pupil is the eye's aperture, while the iris is the diaphragm. In humans and most mammals and birds, the iris (plural: irides or irises) is a thin, annular structure in the eye, responsible for controlling the diameter and size of the pupil, and thus the amount of light reaching the retina.

Blue iris color