Iris (anatomy)

The Iris (Greek Ἶρις, Rainbow '; majority irises or irides ), also called the iris, the colored by pigments iris of the eye. It is as the front portion of the second layer of tissue ( uvea ) of the eye at the junction ( limbus ) of the cornea to the sclera and separates the anterior from the posterior chamber of the eye. The inner edge of the iris, the pupil surrounding that Sehloch, and is as Margo pupillaris on the front surface of the lens. The smooth muscles of the iris regulates the amount of light into the eye ( adaptation).

Muscles of the iris

The iris is with her ​​iris root at the ciliary body and leaves in their midst a free opening, the pupil. Their width is involuntarily controlled by the contraction of muscles: pupillenrandnah leads the annular parasympathetic innervated sphincter pupillae to a narrowing of Sehöffnung. The fan- shaped running at the back of the iris and sympathetic innervated dilator muscle of the pupil dilates the pupil opening. Both cause the pupil game, the involuntary adaptation to different light conditions and adjust the light rays into the eye. The dilatation of the pupil is referred to as mydriasis, the narrowing as miosis.

Both muscles are derived from the outer layer of the optic cup and thus from the neuroectoderm and are composed of smooth muscle.

Feinbau

The iris is composed of two layers. The front part - the stroma - comes with the exception of pigment cells contained from the mesoderm, the posterior part - the pigment layer of the retina and pars iridica - and the pigment cells of the stroma from the ectoderm. The pigment contained in the pigment layer causes scattered light is filtered and the intensity of the incident light is controlled, thereby improving the appearance. The pigment contained in the stroma determines eye color: A high proportion of pigment in the stroma of the iris colored brown, lower it leaves appear green to blue or gray.

Since the structure of the iris stroma in every human being are different, iris recognition is similar to the fingerprint used to identify a person ( biometrics).

Iridology or iris diagnosis claims to be able to make statements about diseases or predispositions of the body by observing the state and variability of the visible iris tissue.

Diseases

In albinism the pigment is completely absent, so that the iris is translucent and appears reddish through the blood vessels of the pigment also poor fundus. The lack of pigment content in this disease is also a reason for the visually impaired of albinos because the iris its aperture function can not meet here: the light penetrates through the iris itself to the built for low brightness sticks and leads to glare and thus disruption of the development of visual function in infancy and early childhood. In many Albinismusformen a malformation of the retina with the fovea absence occurs separately.

The ( congenital or acquired ) the absence of the iris is called aniridia. Defects of the iris is called a coloboma.

The iridocyclitis (inflammation of the iris and ciliary body ) is a symptom of various rheumatic diseases, eg of ankylosing spondylitis, but also occurs as an independent disease.