A lot of people claim their eye color has changed or is changing from time to time and apparently it has nothing to do with imagination.
Melanin is the main chromophore of the human iris. This pigment is considered to be the most important factor that determines the color of the irides. Previous studies based mainly on chemical degradation methods showed that brown irides contain more melanin than blue ones. In our study, we used electron spin resonance (ESR) spectroscopy to detect and characterize melanin free radical centers and associated iron in human irides. Based on this method, we determined the amount of melanin in the irides and the relative content of iron in iridial melanin as a function of their color, shade, and the age of their donors. Chemical degradation of iridial homogenates enabled us to characterize the structure of eumelanin and determine the content of pheomelanin present in human and bovine irides. The ESR amplitude, the normalized intensity obtained by double integration of the ESR signal of melanin, and the content of the pigment in the irides depended on color and shade of the eyes being 40% higher in the brown group of the irides compared with all other groups. On the other hand, the relative iron content normalized to the melanin content in light blue irides showed a small decrease with age of donors. Melanin in human and bovine irides was mostly composed of eumelanin, and pheomelanin content was of the order of a few percent. Although some differences in the structure of eumelanin present in the human and bovine irides are possible, the results obtained in this study suggest that human irides contain eumelanin with very similar chemical properties.
Studies on Caucasian twins, both fraternal and identical, have shown that eye color over time can be subject to change, and major demelanization of the iris may also be genetically determined. Most eye-color changes have been observed or reported in the Caucasian population with hazel and amber eyes.
And then there is heterochromia which refers to a difference in coloration, usually of the iris but also of hair or skin. Heterochromia is a result of the relative excess or lack of melanin (a pigment). It may be inherited, or caused by genetic mosaicism, chimerism, disease, or injury.
A list of people with heterochromia has been published here:
1. Alexander the Great is rumored to have had a hazel eye and a green eye, and according to some stories, may have purposely sought out a horse with unique peepers, too.
2. Kate Bosworth. The actress arguably best known for Blue Crush has one blue eye and one eye that’s blue and hazel.
3. Christopher Walken. As if he needed another reason to be distinctive, Walken shares Bosworth’s blue-and-hazel combo.
4. Kiefer Sutherland. Back when Julia Roberts was dating him, she referenced her then-fiancee’s blue-and-green eyes in an acceptance speech.
5. Michael Flatley. The Lord of the Dance boasts one blue and one green.
6. Jane Seymour. Dr. Quinn would have been able to diagnose this heterchromia right away, even though Seymour’s case is a bit more subtle with one brown and one hazel eye.
7. Dan Aykroyd has the same colors as Jane Seymour. What, you never noticed?
8. Mila Kunis. The Black Swan beauty has a green left eye and a brown right eye.
9. Simon Pegg (one of my favorites). His are blue-grey with brown areas, which he once explained by saying, “I am slightly mutanty.”
Read the full text here: http://mentalfloss.com/article/27273/quick-10-nine-people-heterochromia-and-one-without#ixzz2XoNmgao2
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In the case of David Bowie, his appearance can also possibly attributed to Anisocoria.
More information here.