The iris is usually strongly pigmented, with colors ranging from brown to green, blue, gray and hazel. Occasionally its color is due to lack of pigmentation, as in the white rose of oculocutaneous albinism or darken their pigment by blood vessels, like the red an abnormally vascularised iris (have although human albinos generally very light blue eyes, is as unpigmented color of the human iris a pale blue).
Despite the wide range of colors, there is only one pigment that contributes substantially to normal human iris color, the so-called black pigment melanin. Structurally, this huge molecule is found slightly from the equivalent value in skin and hair.
Physical and genetic factors that determine the color of the iris
Iris color is a very complex phenomenon that the combined effects of texture, pigmentation, fibrous tissue and blood vessels in the iris stroma, which together comprises the epigenetic constitution of an individual. "Eyes" of a person is actually the color of the iris, the cornea is transparent and the white sclera entirely outside the area of interest. This is a common misconception that the iris color is entirely due to its melanin, but it only changes from brown to black.
Melanin is yellowish-brown to dark brown in the stromal pigment cells and black in the pigment epithelium of the iris, which is a thin but very opaque in the back of the iris. Most human irises also show a condensation of the stroma brown melanin in the thin edge, which has an obvious influence on his position all the paint.
The degree of dispersion of melanin, which is in subcellular bundles called melanosomes, has some influence on the observed color, but melanosomes in the iris of humans and other vertebrates are not mobile, and the degree of pigment dispersion can not be undone.
Abnormal clumping of melanosomes does not occur in the disease and lead to changes in iris color (see heterochromia, below) irreversible. Other colors than black or brown are through reflection and selective absorption from other components of the stroma. Sometimes lipofuscin, a yellow "wear and tear" pigment also enters the eye color visible, especially in elderly patients or green eyes (but not in healthy green human eyes).
Blue is one of the possible eye colors in humans. The "blue" allele, which is in the Bey2 and Gey genes of chromosome 15, is recessive. This means that both genes, two blue alleles that have "blue-blue" in a person with blue eyes. If one of the alleles are not "blue" ("green" for Gey or "brown" for Bey2), then the person would have those colored eyes respectively.
Either as an allele (but not both) can be transmitted to offspring, it is quite possible that someone who does not have blue eyes child with blue eyes. Because of his inherited recessively, it is a certainty, if both parents have blue eyes. Although this information gives an overview of the definition of eye color, it is incomplete, and all factors that contribute to eye color and its variation are not fully understood.
Faking the color of the iris
Some eye colors are sometimes seen as particularly attractive, and expression pattern contact lenses are worn to be seen to hide their natural eye color with another. They are rarely needed and almost never seriously recommended by doctors, unless the patient's retina needs extra protection, as in aniridia.
Since the introduction of machines for the automatic analysis, iris patterns and their use in some airports as a security measure is reported that some people have to colored contact lenses, or deliberate iris injury with lasers used to prevent personal identification.
Iris color as paternity test
As already mentioned, although there is so much noise about the genes for eye color, there are no simple genetic determinism for such a complex character, because it is the color of iris pigmentation. Overall, there is no simple Mendelian inheritance in iris color. Therefore, no serious test of paternity based on observations or measurements of iris color, except to note that blue eyes are normally phenotypically recessive, so that a child with brown eyes, two blue-eyed parents can increase doubts about the paternity.
Different colors in both eyes
Heterochromia (as well as aperture or iridium known heterochromia heterochromia) is an eye disease, wherein a membrane is a different color than the other membrane (complete heterochromia), or if the portion of one of the iris of a different color than the remainder (partial heterochromia or sectoral heterochromia).
Occasionally in humans, it is often an indicator of eye diseases such as chronic iritis or diffuse iris melanoma, but can also occur as a normal variant. Sectors or patches of strikingly different colors in the same iris are less common. Alexander the Great and Anastasios I. were baptized (dikoros ", with two pupils") heterochromias for their patents. In her case it was not a true dicoria (two students from the same iris). Real polycoria may due to the disease but usually caused by trauma or previous surgery.
In contrast, heterochromia and iris patterns varied in the usual veterinary practice. Siberian Huskies show heterochromia due to inbreeding, possibly analogous to a genetically-determined Waardenburg syndrome of humans.
Some white cat fancies (eg, white Persians) may show striking heterochromia, with the most common pattern as a uniformly blue, the other green. Altered Input in same Iris is frequently also in some animals, and the standard is in some species.
Several breeds of farm animals, in particular such defined with a blue merle mantle (such Australian Shepherds and Border Collies) can well areas within of a brown iris blue and separated blue eyes and darker show. Some horses (usually within groups, white, spotted, palomino or cremello breeds) can be amber, brown, white, blue, and all in the same eye show no signs of eye diseases.
An eye with an iris white or white-blue is also known as golden
