Why eye color can change as a child (and more rarely as an adult)

When a baby is born, the first images often show his big eyes slate color with mum and dad wondering for days and days: did he have daddy’s green eyes or mum’s dark brown eyes? The months pass, the day of the first birthday arrives and in the photographs that portray the little boy celebrated in front of the giant cake there is no longer any trace of that indefinite gray in the eyes, which will have instead taken on the brown color of the mother. real, A child’s eye color can change. Parents are not even that surprised because it is a frequent phenomenon. But surprisingly, this change can happen even in adulthood and, in this case, there are usually a number of external causes at the base: injuries, infections, sun damage, or even drug interactions.

What Happens Among Infants

Scientific evidence – as the BBC Future – tells us that whether a child’s eye color changes depends very much on the color itself. A study published in 2016 by Cassie Ludwingophthalmologist at Stanford University’s Byers Eye Institute has recorded the color of the iris at the birth of 148 children born at Lucile Packard Children’s Hospital in California. Nearly two thirds of babies are born with brown eyes and one fifth with blue eyes. Two years later Ludwing and his colleagues they found that at the age of two of the 40 babies born with blue eyes, 11 actually had brown eyes, three hazel and two green. Of the 77 babies with brown eyes, nearly all (73) still had brown eyes. So it seemsIt is more common for light eyes to become dark in early childhood, more rarely dark eyes may become lighter. But why? The fact that the most common tendency is a change in the iris towards a darker color (only five out of 148 children had eyes that have lightened with age) is due toaccumulation of a protective pigment in the iris.

The melanogenetic effect

Typically the eyes of anthracite and blue color – confirms Paolo Nucci, full professor of Ophthalmology at the University of Milan – they change color and all become brown and this is a process that usually stops at the eighth month of life. In fact, the melanogenetic effect of the sympathetic system comes into play which helps to produceand melanin in the iris cellshow protective response to irradiation
solar: the neurogenic action is stimulated which causes the eye to become darker. Those with light eyes simply have little melanin. But be careful – warns Nucci – there is no need to keep a newborn in the dark to keep their eyes clear! a question of epigenetics and if the child destined to have dark eyes there is nothing that can change the course of things. Although data on the phenomenon of eye color change are more limited and all refer to the United States, the phenomenon appears to be more common among the native population of northern Europefrom the Pacific Islands or among children of mixed races.

The parallelism with the hair

Just as eye color changes pu change the hair color and there are parallels between the two phenomena: many children who are born very blond grow brown. The color of our hair depends on the melanin, a natural pigment responsible for the coloring of our hair. Whether we are blond, red, brown or black depends on the proportion and concentration of two types of melanin:eumelanin and the pheomelanin. Eumelanin determines the dark shade of the hair while pheomelanin regulates the shade of red. It seems that the production of theeumelanin increases with increasing age and for this reason the foliage darkens as it growsbut the reverse never happens, or very rare.

The distribution of melanin

For the eyes the similar mechanism:
the color determined by the amount of melanin and how it is distributed
. The darker the eyes, the greater the amount of melanin in the iris. Higher levels of melanin can be protective in bright sunlight just like the skin, where the pigment offers greater protection against damage caused by the sun. In irises with little melanin, the blue color comes from the way the collagen fibers in the back of the iris scatter light, in the same way that the sky appears blue due to the way the light disperses into the atmosphere.

A congenital difference

Having irises of a different color from birth is still possible, albeit rare. In this case we speak of heterochromiaone somatic characteristic that affects less than 1% of the population and that is caused by a different concentration of melanin in the two eyes: the eye in which the most concentrated pigment appears tending to brown, while the other is lighter. Among the famous people who have this feature are Johnny Dorelli, Jane SeymourTOlice Eve, Dominic Sherwood, but also historical leaders like Alexander the Great. It is said of the latter that he had a hazel eye and a green one and that he pretended to ride steeds with the same characteristics. Moreover, this particularity is not exclusive to mankind, but rather more frequent (reaches about 5%) in some animals, such as horse, cat and dog. If different shades are present within the same iris, it is referred to as somatic mosaicism. An example is that of the actress Kate Bosworth, whose right eye is half blue and half hazel. These are all congenital conditions, that is, present from birth, which do not involve consequences or damage to health.

Injuries, infections, sun damage: the other causes of change

Although heterochromia is an essentially harmless condition, many of the changes in eye color, especially in adulthood, can sometimes be related to something more serious such as injuries, infections, sun damage, or even the use of certain medications.In the Caucasian population, the eyes may lighten in adulthood because the pigments deteriorate and the iris becomes greyish, recalls Nucci. However, there are viral or immune pathologies that interact with the pigment and can change the color of the iris, adds the professor.

One of the most famous eye changes due to an injury involved the left eye of David Bowie. As a child he had both clear eyes but as a kid during a fight over a girl he was hit with a punch in the left eye. The injury
caused paralysis of the muscles that contract the iris, the so-called iris stupor. Since that time his left pupil remained perpetually expanded, therefore darker explains Nucci. On the other hand, the color of the irises has not changed.

it is easier to still be ainfection the cause of a color difference in the irises. A famous case of heterochromia that of the actress Mila Kunis, whose right eye brown and left green. Kunis heterochromia results from an infection of the iris, which has destroyed some of the pigment in the left eye. Some infectious diseases can cause the pigment to disappear. One of these is Fuch’s heterochromic cyclitis, caused by a viral infection, often rubella, but not limited to This is a form of inflammation that usually affects only one eye, causing a loss of iris pigment. Thus the diseased eye gradually becomes less pigmented than the other. Another disease that can cause heterochromia is the pigmentary glaucoma, a particular form of glaucoma caused by the abrasion of the iris pigment that is released in the eye and which can be distributed differently in the two eyes. Even the nevus of Ota, a very rare form of unilateral ocular melanoma, gives a typical hypercolouration of the iris, which makes the affected eye appear very dark. Finally, in some forms of uveitis, typical inflammatory nodules form on the surface of the iris which can cause dyschromia. In an extremely rare case, a Ebola survivor suffered a change in eye color from blue to greenIt was found that the virus persisted in the eye fluid after it was cleared from other parts of his body. Finally – concludes Nucci – there are also some antiglaucoma drugs that can modify the pigmentation of the iris in adulthood.