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How our eyes can change colour throughout our lives - BBC

How our eyes can change colour throughout our lives - BBC

How our eyes can change colour throughout our lives - BBC
Sep 30, 2022 1 min, 57 secs

Nearly two-thirds of babies were born with brown eyes, and one-fifth with blue.

Two years later, Ludwig and her colleagues found that of the 40 blue-eyed babies in the study, 11 had brown eyes by the age of two, three had hazel, and two had green.

It appears, then, that blue eyes are much more likely to change than brown eyes during the early stages of our lives.

One clue lies in the fact that when the babies' eyes did change colour, they tended to become darker, not lighter.

In Ludwig's study, one-third of the babies' eyes changed colour in their first two years, with the most common change being eyes becoming darker.

After becoming curious about the phenomenon of eye colour change, Mackey found that these two studies were more or less all the research that had been done on childhood eye-colour change.

Anecdotally, he found that it was not uncommon for parents to expect that their babies' eyes would change colour.

"I heard parents and their friends saying, 'Oh, yes, the baby's been born with blue eyes, but that will change over the next few years'," he says.

Though the data is limited and has only been carried out in just one country, the US, changes in eye colour appears to be most common among people with Northern European, Pacific Islander or mixed-race heritage.

"You'll see photos of some children who are blonde as babies, but they've got quite dark brown hair when they become older," says Mackey.

Humans are not the only animals whose eyes change colour.

Perhaps the most dramatic change is the seasonal variation in reindeer eyes, from golden-turquoise in summer to deep blue in winter.

In irises with little melanin, the blue colour comes from the way the fibres of collagen at the back of the iris scatter light, in the same way that the sky appears blue because of way light is scattered in the atmosphere.

As to why some children's eyes express more melanin over time, this remains mystery, says Mackey.

"We actually don't know what influences those colour changes," says Mackey, but there could well be an environmental factor at play.

However, the punch didn't change the blue colour of Bowie's irises, it was the enlarged pupil that made his left eye look darker

It is, however, possible for injury to alter iris colour, says Mackey

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