Eye color and Tyndall Effect


According to wiki:"Eye color is a polygenic phenotypic character determined by two distinct factors: the pigmentation of the eye iris and the frequency-dependence of the scattering light by the turbid medium in the stroma of the iris."

 Eye color often is the genetic trait that fascinates parents the most as a child develops. Will the child's eyes be black, brown, blue, gray, green, hazel or some combination of colors? 

 Human eye color originates with three genes, two of which are well understood. These genes account for the most common colors — green, brown, and blue. Other colors, such as gray, hazel and multiple combinations are not fully understood or explainable at this time.

 The pigmentation of the iris depends on the concentration of melanin in the iris pigment epithelium(located on the back of the iris), the melanin content within the iris stroma (located at the front of the iris), and the cellular density of the stroma.The appearance of blue and green, as well as hazel eyes, results from the Tyndall scattering of light in the stroma.
Neither blue nor green pigments are ever present in the human iris or ocular fluid.Eye color is thus an instance of structural color and varies depending on the lighting conditions, especially for lighter-colored eyes.

 So what's Tyndall Scattering?It is similar to Rayleigh scattering, in that the intensity of the scattered light depends on the fourth power of the, so blue light is scattered much more strongly than red light. It was named after a 19th century physicist John Tyndall.Under the Tyndall effect, the longer-wavelength light is more while the shorter-wavelength light is more reflected via scattering.

 But the scattering of the sky due to which it appears blue is not due to Tyndall Effect but due to Rayleigh scattering.because the scattering particles are the molecules of the air, which are much smaller than the wavelength of the light.Tyndall effect deals with particles of much larger size than that of wavelength of visible light.

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