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Where Does the Color of Your Eyes Come From?

Eye colors can range from the most common color, brown, to the least common, green. Eye color is an inherited trait influenced by more than one gene. The actual number of genes that contribute to eye color is currently unknown, but there are a few likely candidates. A recent study found that it was possible to predict the color of eyes with more than 90% accuracy for brown and blue.

Eye color is determined by the amount and type of pigments in the eye's iris. Humans and other animals have many variations in eye color, as blue, brown, grey, green, and others. The genetics of eye color are complicated, and color is determined by multiple genes. The once-held view that blue eye color is a simple recessive trait has been shown to be incorrect. The genetics of eye color are so complex that almost any parent-child combination of eye colors can occur.

In human eyes, these variations in color are attributed to varying ratios of a form of melanin produced in the iris. The brightly colored eyes of many bird species are largely determined by other pigments.

Genetic determination of eye color

Eye colors can range from the most common color, brown, to the least common, green. Eye color is an inherited trait influenced by more than one gene. The actual number of genes that contribute to eye color is currently unknown, but there are a few likely candidates. A recent study found that it was possible to predict the color of eyes with more than 90% accuracy for brown and blue.

Classification of color

Iris color can provide a large amount of information about an individual, and a classification of various colors may be useful in documenting pathological changes or determining how a person may respond to various eye pharmaceuticals. As the perception of color depends on viewing conditions (e.g., the amount and kind of illumination, as well as the hue of the surrounding environment), so does the perception of eye color.

Changes in eye color

In all populations, children are most commonly born with unpigmented eyes. However, most babies who have European ancestry have light-colored eyes before the age of one. As the child develops, certain cells found within the iris of human eyes, as well as skin and hair follicles slowly begin to produce melanin. Because these cells continually produce pigment, in theory eye color can be changed.

Most eye changes happen when the infant is around one year old, although it can happen up to three years of age. Observing the iris of an infant from the side using only transmitted light with no reflection from the back of the iris, it is possible to detect the presence or absence of low levels of melanin. An iris that appears blue under this method of observation is more likely to remain blue as the infant ages. An iris that appears golden contains some melanin even at this early age and is likely to turn green or brown as the infant ages.

Changes (lightening or darkening) of eye colors during puberty, early childhood, pregnancy, and sometimes after serious trauma, do represent a case for to state that some eyes can or do change, based on chemical reactions and hormonal changes within the body.

Amber Eyes

Amber eyes are of a solid color and have a strong yellowish/golden and russet/coppery tint. This might be due to the deposition of the yellow pigment in the iris (which is also found in green eyes). Amber eyes should not be confused with hazel eyes; although hazel eyes may contain specks of amber or gold, they usually tend to comprise many other colors, including green, brown and orange. Also, hazel eyes may appear to shift in color and consist of flecks and ripples, while amber eyes are of a solid gold hue. Even though amber is considered to be like gold, some people have russet or copper colored amber eyes which many people mistake for hazel, though hazel tends to be duller and contains green with red/gold flecks, like mentioned above. Amber eyes may also contain amounts of very light goldish gray, found in animals like wolves.

Blue eyes contain low amounts of melanin within the iris; the outer surface of the iris of a blue-eyed person is clear, lacking the outer layer of pigmentation that is found in brown eyes. Their color is caused by the inner layer of pigmentation and the semi-opaque fibrous tissues that lie between the two layers.

Genetics

Brown eyes are dominant in humans, and in many parts of the world, it is nearly the only iris color present. It is less common in countries around the Baltic Sea and in Scandinavia. Dark pigment of brown eyes is most common in East Asia, Southeast Asia, South Asia, West Asia, Oceania, Africa, Americas, etc.

Light or medium-pigmented brown eyes are common in Europe, Iran, Afghanistan, Armenia, Pakistan and Northern India, as well as some parts of the Middle East. Light-pigmented brown eyes are sometimes referred to as "honey eyes".

In humans, brown eyes contain large amounts of melanin within the iris, which serves to absorb light at both shorter and longer wavelengths. Brown eyes are the most common eye color, with over half of the world's population having them.

Gray eyes are most common in Northern and Eastern Europe. Gray eyes can also be found in parts of North West Africa among the Algerian Shawia people and in the Middle East, most notably in Iran, Afghanistan, and Pakistan. Under magnification, gray eyes exhibit small amounts of yellow and brown color in the iris. Ultimately, there are at least two things that determine gray eye color. The first is the amount of melanin made, and the second is the density of the proteins in the supporting tissue of the eye.

Hazel

Hazel eyes often appear to shift in color from a brown to a green. Although hazel mostly consists of brown and green, the dominant color in the eye can either be brown/gold or green. This is how many people mistake hazel eyes to be amber and vice versa.

Medical implications

Those with lighter iris color have been found to have a higher prevalence of age-related macular degeneration than those with darker iris color; however, a recent study suggests that people with dark brown eyes are at increased risk of developing cataracts and therefore should protect their eyes from direct exposure to sunlight.

Eye color may also be symptomatic of disease. Aside from the iris, yellowing of the whites of the eyes is associated with jaundice and symptomatic of liver disease, including cirrhosis, hepatitis and malaria. Yellowing of the whites of the eyes in people with darker pigmented skin is often due to melanin being present in the whites of the eyes. However, any sudden changes in the color of the whites of the eyes should be addressed by a medical professional.

Reference: Wikipedia Commons

Images: Stock.xchng

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Comments (5)

Interesting and very informative

Is there any reason why some persons eye colors seem to change according to the color clothing, blouse or shirt, they are wearing? Very interesting Colin.

Good observation Beverly Anne - not sure why myself.....but I am going to find out now!

Good information.

Very, very interesting Colin.

Quite interesting.Thanks.

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