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The sclera's blood vessels are mainly on the surface. Along with the vessels of the conjunctiva (which is a thin layer covering the sclera), those in the episclera render the inflamed eye bright red. [6] In many vertebrates, the sclera is reinforced with plates of cartilage or bone, together forming a circular structure called the sclerotic ring.
According to traditional Chinese and Japanese face reading, the eye is composed of two parts, the yin (black, iris and pupil) and the yang (white, sclera).The visibility of the sclera beneath the iris is said to represent physical imbalance in the body, and is claimed to be present in alcoholics, drug addicts, and people who over-consume sugar or grain.
The uvea (/ ˈ j uː v i ə /; [1] derived from Latin: uva meaning "grape"), also called the uveal layer, uveal coat, uveal tract, vascular tunic or vascular layer, is the pigmented middle layer of the three concentric layers that make up an eye, precisely between the inner retina and the outer fibrous layer composed of the sclera and cornea.
Unlike other primates, all human beings have eyes with a distinct colour contrast between the white sclera, the coloured iris, and the black pupil. This is due to a lack of pigment in the sclera. Other primates mostly have pigmented sclerae that are brown or dark in colour. There is also a higher contrast between human skin, sclera, and irises.
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.
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Eye color inheritance is now recognized as a polygenic trait, meaning that it is controlled by the interactions of several genes. [55] In 2008, a team of researchers from the University of Copenhagen located a single mutation that causes the phenomenon of blue eyes. The research was published in the Journal of Human Genetics.