värikalvon

Värikalvon, also known as the iris, is the colored part of the eye. It is a thin, annular structure that controls the amount of light reaching the retina by adjusting the size of the pupil. The iris is composed of two muscles: the sphincter pupillae, which constricts the pupil, and the dilator pupillae, which dilates it. The color of the iris is determined by the amount and type of melanin pigment present in the stroma, the outermost layer of the iris. More melanin results in darker eyes, while less melanin results in lighter eyes. Albinism, a genetic condition, can cause a complete lack of melanin, resulting in very pale blue or pink irises. The iris also contains blood vessels and nerves. The pattern of the iris is unique to each individual, making it a potential biometric identifier. Conditions affecting the iris include iritis (inflammation), heterochromia (difference in iris color between eyes or within the same eye), and coloboma (a developmental fissure).