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Different eye colors in humans: as they say, causes
Medical expert of the article
A rare condition in which the eyes of different colors - is heterochromia. It is congenital and acquired, occurs in humans and animals. Consider the features of this anomaly.
The main types of hereditary heterochromia according to the degree of staining of the iris: 
- Full - one of the most common types, each eye has its own color.
- Sector - the iris of one eye consists of several shades.
- Central - the iris has several colored rings.
Types of acquired anomalies due to lesions of the iris: 
- Simple - staining due to weakness of the cervical sympathetic nerve.
- Complicated - caused by chronic diseases in which one eye completely changes its color.
- Metalloznaya - occurs due to contact with metal fragments in the eyes, which provoke the development of siderosis or chalcosis.
Most often, women face this anomaly. It does not affect visual acuity and does not cause painful symptoms, therefore it is absolutely safe.
What is the name of the eyes of different colors?
The abnormal condition in which the eyes have a different color is heterochromia. It occurs due to the combination of pigments in the stroma of the iris. This happens with genetic disorders or the action of external factors.
People with this deviation perceive colors as well as healthy ones. If the phenomenon is of hereditary origin, then medical correction is not required.
When changes are caused by injuries and other pathological factors, visual impairment may be impaired and ophthalmologic diseases may occur. This condition requires a comprehensive diagnosis and treatment.
Why are the eyes of different colors?
The eyes of different flowers are due to the lack or excess of the melanin pigment in the iris or part of it. The pigment content in the iris stroma and the anterior boundary layer determines all shades of the color of the iris from green to dark brown. An increase in pigment in the stroma of the iris leads to a greater absorption of light and, as a result, to a darker eye color.
Melanin is an inert biopolymer that exists in two different forms: brown-black eumelanin and red-yellow pheomelanin. Melanocytes have the ability to produce both forms of melanin; However, the ratio of these two forms can vary widely in people, producing different shades of hair and skin color.
In the first decade of the 20th century, two messages appeared in the literature that supported the idea that eye color is inherited as a simple Mendelian trait. Brown eyes were inherited as the dominant trait, and blue eyes were recessive, and as a result, two blue-eyed parents were unable to give birth to children with brown eyes. Although this doctrine was widespread, it soon became apparent that sometimes blue-eyed parents could produce offspring with brown eyes, and this eye color is not inherited as a simple Mendelian trait. Indeed, recent studies show that eye color is inherited as a polygenic trait, which is still not fully understood.
A number of genes are involved in determining eye color: these include OCA2, TYRP1, MAPT and MYO5A. Of these, the OCA2 and EYCL3 genes, which are located on the long arm of chromosome-15 (15q11.2–15q-12), encode brown / blue eye color (BEY) and EYCL1, which is on chromosome 19, which encodes green / blue eye color ( GEY) seems to be the most influential.
After birth, the color of the iris may change, and in Caucasians, the iris of the newborn is blue due to a lack of stromal melanocytes, which, apparently, have not yet migrated from the neural crest or are not differentiated from the progenitor stem cells. In the black race, the iris at birth looks gray. The iris usually takes its true color at the age of 3-5 months.
There are also causal factors that can trigger the development of heterochromia at any age: 
- Inflammation of the choroid in Fuchs syndrome causes a change in one or two eyes, blurred vision, and in severe cases, complete loss of vision.
- Side effect of drugs used in the treatment of glaucoma.
- Iridocorneal endothelial syndrome.
- Malignant neoplasms of the iris, neurofibromatosis. 
- Hemorrhages in the eyeball, sclera.
- Eye injuries - hitting the organs of vision of metal chips, graphite and other foreign objects leads to a change in the color of the injured eye.
- Waardenburg syndrome - an uneven distribution of melanin in the upper layer of the iris. 
There are also a number of systemic diseases that lead to changes: mosaicism, chimerism, Wilson-Konovalov disease, leukemia or lymphoma, Stilling-Türk-Duane syndrome and other pathologies.
Famous people with different eye color
Different color of the left and right eyes or heterogeneity of the color distribution in one organ of vision is heterochromia. This phenomenon is associated with impaired normal levels of melanin in the iris. About 2% of the Earth lives with the anomaly, including famous people:
- David Bowie - the famous rock musician, in his youth injured his eyes. The injured organ completely lost its ability to perceive color and acquired a brown tint.
- Alice Eve - British actress with the full form of heterochromia. Her right eye is green and her left eye is blue.
- Mila Jovic - American actress, model and fashion designer. One girl's eye is blue, and the second is green. During filming, she chooses one color, and the second adjusts with a color lens.
- Sarah McDaniel is an American Playboy model and a popular blogger. One of her eyes is blue, the other is brown. This feature attracted worldwide attention to it.
- Josh Henderson is an American actor and singer. The owner of the unique shades of the iris - sky blue and bright green.
- Jane Seymour is a British actress who is on the list of the sexiest girls of agent 007. She has one brown eye and the second one is green.
- Kate Bosworth - American model and actress. The winner of the sector anomaly is one blue eye, and the second with a brown patch.
- Henry Cavill is a popular British actor with a sectoral heterochromia. It has blue eyes with a brown sector in the upper part of the left organ.
- Mila Kunis - American actress, one of the sexiest women in the world. One of her eyes is green and the other is light brown.
- Demi Moore is an American actress, her left eye is green and her right eye is brown.
In addition to real celebrities, there are literary heroes with eyes of different colors: Lieutenant Myshlayevsky from the “White Guard” and Woland from the “Master and Margarita” by Mikhail Bulgakov. The protagonist of the work "The Four Tankmen and the Dog" by Janusz Pshimanovsky, as well as Tirion Lanister from "The Game of the Prekstolov" by George Martin.