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The irises of human eyes exhibit a wide spectrum of colours. Eye color is a polygenic phenotypic trait determined by two factors: the pigmentation of the eye's iris [1] [2] and the frequency-dependence of the scattering of light by the turbid medium in the stroma of the iris.
While the spectrum of eye colors is as vast as the human experience itself, ... 8-10 percent of the world's population have blue eyes. ... There are also rare cases of violet and red-colored eyes.
In sectoral heterochromia, areas of the same iris contain two different colors, the contrasting colors being demarcated in a radial, or sectoral, manner. Sectoral heterochromia may affect one or both eyes. [31] It is unknown how rare sectoral heterochromia is in humans, but it is considered to be less common than complete heterochromia.
The inheritance pattern followed by blue eyes was previously assumed to be a mendelian recessive trait, however, eye color inheritance is now recognized as a polygenic trait, meaning that it is controlled by the interactions of several genes. [57] Blue eyes are predominant in northern and eastern Europe, particularly around the Baltic Sea.
According to CNN, Dr. Gary Heiting, a licensed optometrist and senior editor of All About Vision explained why all human eyes are actually brown, no matter if they look blue or greenish.
Hazel eyes tend to change colors due to Rayleigh scattering—the same factor that makes the sky appear blue. This optical effect occurs in the stroma, which is a thin layer of tissue in front of ...
Blue eyes are also found in parts of Western Asia, most notably in Afghanistan, Syria, Iraq, and Iran. [53] In Estonia, 99% of people have blue eyes. [54] [55] In Denmark in 1978, only 8% of the population had brown eyes, though through immigration, today that number is about 11%. [55] In Germany, about 75% have blue eyes. [55]
Waardenburg syndrome is a group of rare genetic conditions characterised by at least some degree of congenital hearing loss and pigmentation deficiencies, which can include bright blue eyes (or one blue eye and one brown eye), a white forelock or patches of light skin.