Eyes that change color are a mysterious phenomenon

It’s always amazing how a newborn’s eye color can change drastically in just two years. Amazing and sometimes confusing, because it is a physical property that many of us attach great importance to. It’s a science: eye color can have an effect on the degree of confidence to witness to someone.

BBC journalist He was interested in these color changes, which most often occur during the first years of life, but can also occur at other times of life. These changes can be caused by many factors, including excessive sun exposure, infection or injury –This was the case for David Bowie, whose eyes are abnormally mismatched. But the discoloration can also happen spontaneously, without any real cause.

Returning to children, an American study shows that the vast majority of people born with brown eyes retained the same color at the age of two (in the studied sample, this represents almost 95% of cases). In contrast, blue-eyed children are more susceptible to mutations: after two years, their eyes may turn brown, hazel or green.

Another US study of the age at which a color change can occur has established that for 80-90% of individuals, the color has been permanently fixed before the age of 6 years – with some imperceptible nuances. In the rest of the cases, the eyes can continue to change color during adolescence, or even into adulthood. It has also been observed that in heterozygous twins, initially similar eye colors can end up diverging.

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like the blue sky

The color of the eyes depends in particular on the amount of melanin, this pigment also responsible for the color of the skin. It plays an important role In protection from the sunwhich explains why lighter eyes are more fragile, while black or brown eyes are more resistant.

Journalist Martha Henricks explains that the blue color in the iris with little melanin, is due to the way the collagen fibers diffuse light. This phenomenon is similar to what happens in the sky: it’s the way light is scattered in the atmosphere making it blue.

All this does not explain why so many children produce more melanin as they grow, and therefore why their eyes tend to darken. “We don’t know what influences these color changes.”admits David Mackey, Australian professor of ophthalmology. “As is often the case, it is the result of the interplay between genetics and the environment. But what environmental factors have an effect? ​​We don’t have that kind of data.”

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