The human iris The iris is the grey-brown area. The other structures visible are the transparent pupil (showing as black), the white outer sclera, of which the central part, the cornea, is transparent.In anatomy, the iris (correct classical plural, irides) is the most visible part of the eye of vertebrates, including humans. The following covers the iris of vertebrates, not the separately evolving iris found in some cephalopods. The word comes from Greek mythology, in which Iris is the personification of the rainbow.
The iris is an annulus (or flattened ring) consisting of pigmented fibrovascular tissue known as a stroma. The stroma connects a sphincter muscle, which contracts the pupil, and a set of dialator muscles which open it. The back surface is covered by a two-cell thick epithelial layer, the iris pigment epithelium, but the front surface has no epithelium. The outer edge of the iris, known as the root, is attached to the sclera and the anterior ciliary body. The iris and ciliary body together are known as the anterior uvea. Just in front of the root of the iris is the region through which the aqueous humour constantly drains out of the eye, with the result that diseases of the iris often have important effects on intra-ocular pressure, and indirectly on vision.