Date the perfect transparency of the cornea, the iris is the most visible part of the eye, that which defines eye color in relation to the quantity and characteristics of melanin distributed on its surface (dimensions of the granules and their characteristics), determining ultimately, the color. The iris is what is the diaphragm in the camera and through the variation of pupillary diameter (pupil)is able to adjust the amount of light that reaches the macula.
Anatomically, the iris is the diaphragm muscle that regulates the amount of light which must enter the eye in various lighting conditions and is composed of fibrovascular tissue pigmented (stroma irideo) and muscle. We distinguish 3 areas in the iris: the portion ciliary or body, the collarette and the pupillary area (close to the pupil) and two muscles with opposite functions: it sphincter of the pupil responsible for pupillary constriction, and muscle pupillary dilator the fact that dilates. L'iride ed il ciliary body are l'uvea anteriore (the rear is instead given by choroid). In its posterior portion of the iris is compared with the epithelium of the ciliary processes where product is the aqueous humor. Inflammation of the iris direct (this iriti, iridocyclitis) can give increased eye pressure thus affecting its motility and vision.