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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.
The human eye's red-to-green and blue-to-yellow values of each one-wavelength visible color [citation needed] Human color sensation is defined by the sensitivity curves (shown here normalized) of the three kinds of cone cells: respectively the short-, medium- and long-wavelength types.
Sufficient differences in wavelength cause a difference in the perceived hue; the just-noticeable difference in wavelength varies from about 1 nm in the blue-green and yellow wavelengths to 10 nm and more in the longer red and shorter blue wavelengths. Although the human eye can distinguish up to a few hundred hues, when those pure spectral ...
Although the processes determining eye color are not fully understood, it is known that inherited eye color is determined by multiple genes. Environmental or acquired factors can alter these inherited traits. [7] The color of the mammalian, including human, iris is very variable. However, there are only two pigments present, eumelanin and ...
The second most common type responds the most to light of yellow to green medium-wavelength, peaking at 530 nm. M cones make up about a third of cones in the human eye. The third type responds the most to blue short-wavelength light, peaking at 420 nm, and make up only around 2% of the cones in the human retina.
Blue eyes are also found in southern Europe, Central Asia, South Asia, North Africa and West Asia. [57] [58] Approximately 8% to 10% of the global population have blue eyes. [34] A 2002 study found that the prevalence of blue eye color among the white population in the United States to be 33.8% for those born from 1936 through 1951.
The human eye is relatively insensitive to indigo's frequencies, and some people who have otherwise-good vision cannot distinguish indigo from blue and violet. For this reason, some later commentators, including Isaac Asimov, [13] have suggested that indigo should not be regarded as a color in its own right but merely as a shade of blue or ...
Colors of confusion include blue/purple and green/yellow. [2] Deuteranopia is a severe form of red-green color blindness, in which the M-cone is absent. It is sex-linked and affects about 1% of males. Color vision is very similar to protanopia. [2] Tritanopia is a severe form of blue-yellow color blindness, in which the S-cone is absent. It is ...