The Mystery Of Newborn Blue Eyes Unveiled

The eye colour of a newborn baby is determined by the amount of melanin in the iris, with blue eyes having very little melanin and brown eyes having a lot. Melanocytes are the cells that create melanin and respond to light, so a baby's eye colour can change as they are exposed to more light. While some babies are born with their final eye colour, others experience changes as melanocytes ramp up melanin production.

The most dramatic eye colour changes will probably occur when a baby is between three and six months old, but eye colour can continue to change for several years. In rare cases, eye colour can change into adolescence and even adulthood.

Melanin levels determine eye colour

The eye's iris has varying levels of pigmentation, which ranges from light brown to black, depending on the concentration of melanin in the iris pigment epithelium (located on the back of the iris) and the melanin content within the iris stroma (located at the front of the iris). The appearance of blue, green, and hazel eyes results from the Tyndall scattering of light in the stroma, a phenomenon similar to Rayleigh scattering, which accounts for the blue sky.

The colour of a newborn's eyes depends on the amount of melanin in the iris. If there is very little melanin in the iris, the eyes will be blue. A bit more melanin results in green eyes, and even more will make them hazel or light brown. A high concentration of melanin will make the eyes medium or dark brown.

The amount of melanin in a baby's eyes at birth is also influenced by the amount of light exposure. When a baby is born, they are exposed to more light than they were in the womb, which kick-starts melanin production in the iris and can lead to eye colour changes.

The final eye colour of a baby is determined by genetics, with multiple genes determining the amount and quality of melanin present in the iris. However, it is challenging to predict a baby's eye colour based on their parents' eye colours due to the complex variations and interactions of genes.

Most individuals achieve stable eye colour by 6 years of age. However, a subpopulation of 10% to 15% of Caucasians can experience changes in eye colour throughout adolescence and into adulthood.

Melanocytes respond to light

Melanocytes are cells that produce melanin, a pigment that gives colour to the skin, hair, and eyes. Melanocytes in the eyes are located in the iris and the choroid.

Here's a more detailed explanation of the process:

The Role of Melanocytes in Eye Colour

The colour of the iris, the muscular ring that surrounds the pupil of the eye, depends on the amount of melanin it contains. Melanin is produced by melanocytes, which are special cells that also give colour to the skin and hair.

When a baby is born, their eyes may appear grey or blue due to a lack of pigment and because they have been in a dark womb. As the baby is exposed to more light, their eye colour can change over time, even up to several years. This is because the melanocytes respond to light by producing more melanin, which can result in eye colours such as blue, green, hazel, or brown.

How Melanocytes Respond to Light

Melanocytes contain rhodopsin, a photosensitive receptor that is usually found in the eyes. When melanocytes are exposed to ultraviolet (UV) light, particularly long-wavelength UVA light, the rhodopsin detects this light and triggers a response.

Within seconds of UVA light exposure, rhodopsin triggers calcium signals in the melanocytes, which then leads to the production of melanin within an hour. This process is known as melanogenesis, and it results in the darkening of the iris as more melanin is produced and deposited.

The amount of melanin produced depends on the activity of the melanocytes and the individual's genetic makeup. People with darker skin are more likely to have brown eyes due to higher levels of melanin, while light-skinned newborns often have blue or grey eyes that can change colour over time.

The Protective Role of Melanin

Melanin plays an important role in protecting the eyes against the harmful effects of UV radiation, which can cause ocular diseases such as uveal melanoma and age-related macular degeneration. By absorbing UV radiation, melanin acts as a photo-screen, blocking the light from reaching the sensitive tissues at the back of the eye.

Additionally, melanin can act as an antioxidant, protecting the eye from oxidative damage caused by reactive oxygen species (ROS). However, with age, the antioxidant properties of melanin may diminish, and it can even become pro-oxidant, contributing to age-related macular degeneration.

Blue eyes are less common than brown

The colour of a newborn's eyes depends on the amount of melanin in the iris. Melanocytes are special cells that produce melanin, which also gives skin its colour. Melanocytes respond to light, so a baby may have eyes that appear grey or blue due to the lack of pigment and because they have been in a dark womb.

Blue eyes have the least amount of melanin. Brown eyes, on the other hand, have the most melanin and are the most common eye colour worldwide. In a 2020 study, 79% of people worldwide were found to have brown eyes. Brown eyes are also more common in hotter climates, with around 50% of the world's population having brown eyes. In the US, that number is lower, at about 45%. In countries like Iceland, however, blue is the majority eye colour.

Blue is the second most common eye colour globally, with 8 to 10% of the world's population having blue eyes. In the US, that number is higher, at about 27%. All people with blue eyes share the same genetic trait, meaning they likely descend from a common ancestor.

The colour of a newborn's eyes can change over time as they are exposed to more light. Melanocytes are most active in the first year of life, and by the time a baby is 9 months old, they will usually have their permanent eye colour. However, it can take up to three years for a child's eye colour to settle.

Eye colour can change into adulthood

The eye colour of a newborn baby is not necessarily their final eye colour. The colour of a baby's irises depends on the amount of melanin, a pigment produced by cells called melanocytes, which also gives skin its colour. Melanocytes respond to light, and a baby's eyes may appear grey or blue due to the lack of pigment in a dark womb. As a baby is exposed to more light, their eye colour can change over time, even up to several years.

The most dramatic eye colour changes will probably occur when a child is between three and six months old. By this point, the iris will have produced enough pigment to better predict the final hue. However, a baby's eye colour may continue to change due to pigmentation of the iris until their first birthday, and even up to three years old.

While brown eyes are likely to remain brown throughout life, blue eyes can become brown or green, and green eyes can deepen into hazel or brown. The final eye colour depends on genetics, with multiple genes determining the amount and quality of melanin present in the iris.

If both biological parents have blue eyes, their baby is likely to have blue eyes. If both parents have brown eyes, their baby is likely to have brown eyes. If one parent has blue eyes and the other brown, the baby has a 50-50 chance of having blue eyes. If one of the baby's grandparents has blue eyes, their chances of having blue eyes are higher.

Eye colour is influenced by genetics

The colour of a newborn's eyes is influenced by genetics. Melanin, which is produced by melanocytes, is responsible for eye colour. Melanocytes are special cells that produce the pigment melanin, which also gives skin and hair their colour. The more melanin present in the top layer of the iris, known as the epithelium, the darker the eye colour.

The amount of melanin in the iris is influenced by genetics, with multiple genes determining the amount and quality of melanin present. The OCA2 gene, for example, is involved in the production of melanin. A genetic mutation affecting this gene can cause a switch that limits the production of melanin in the iris, resulting in blue eyes. This mutation is estimated to have occurred 6,000-10,000 years ago in an individual in northern Europe.

The final eye colour of a newborn depends on the amount of melanin produced by the melanocytes. If the melanocytes secrete a little more melanin, the baby may have blue eyes. With a bit more melanin, their eyes may be green or hazel, and with even more, their eyes will likely be brown. Brown eyes are the most common eye colour, and they tend to remain brown throughout life.

While genetics play a significant role in determining eye colour, other factors also come into play. The amount of light exposure can affect melanin production in the iris, influencing eye colour. Additionally, the interplay of genes is complex, and it can be challenging to make definitive predictions about a baby's eye colour based solely on the eye colours of their parents.

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