Iris (anatomy)

In anatomy, the iris (plural irises or 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.

Related Topics:
Anatomy - Eye - Vertebrate - Human - Cephalopod - Greek mythology - Iris

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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 intraocular pressure, and indirectly on vision.

Related Topics:
Stroma - Sphincter - Pupil - Epithelia - Aqueous humour - Intraocular pressure

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