Where does eye colour come from?

Tuesday, 5 February 2019 by Vision Direct

Explore exactly what determines eye colour

Most people are fascinated by eye colour, mainly because everyone's eyes are completely unique, just like fingerprints. Even when people have similar shades, the concentration of colour can be very different. Eye colour includes the following range: blue, amber, brown, grey, green and hazel. Some people even say your eye colour can be an indicator of personality.

The most common eye colour is brown, accounting for roughly 80% of people globally. Around 8-10% of people in the world have blue eyes, 5% have amber or hazel eyes, and 2% of people have green eyes, making it the rarest colour. At Vision Direct, we're always keen to see the world through someone else's eyes so we thought we'd explore exactly what determines eye colour.

Where does eye colour come from?

Where does eye colour come from?

The coloured part of the eye is called the iris - a thin circular structure which is responsible for controlling the diameter and size of the pupil. The iris contains pigmentation, called melanin. Two main factors contribute to the way in which this pigmentation determines eye colour:

  • The genetic information you receive from your parents affects this pigmentation.
  • The distribution of pigmentation in the iris affects the way in which light is scattered as it passes through the eye.
How melanin patterns affect eye colour

How melanin patterns affect eye colour

Eye colour is the result of variations in the amount of melanin we have. If little melanin pigment is present it results in blue eyes, a little more pigment gives green eyes and lots of pigment gives brown eyes.

Some people have eyes that have different coloured patches which reflect the varying concentrations of melanin. For example, you will often see blue eyes with a green or brown circle around the pupil. In these eyes, different parts of the iris make different amounts of melanin.

How eye colour genes work

How eye colour genes work

Each of your body's cells has 46 chromosomes, divided into 23 pairs. When you were conceived, you inherited one chromosome from each parent to make each pair of your chromosomes. Chromosomes are made up of a particular part of DNA called genes. These genes, which also come in pairs, determine many of your physical characteristics. Scientists believe that up to 16 different genes could play a role in deciding your eye colour.

Our genes tell a cell in the iris to make specific amounts of the dark pigmentation called melanin. The more melanin produced, the darker the eye colour will be. Genes which bring about higher levels of melanin, creating brown eyes, are dominant over genes which produce lower levels of melanin, making blue eyes. This means that when you inherit a brown eye gene, it will win out over a blue eye gene.

Because melanin production does not begin at birth, babies' eyes appear blue. It's usually not until around the age of three that a child's true permanent eye colour reveals itself. The two main genes responsible for eye colour are OCA2 and HERC2, both of which are part of chromosome 15. It's important to remember that people with different coloured eyes don't have different eye colour genes, just have different versions of the same genes.

Can eye colour change?

Can eye colour change?

Have you noticed how some people's eyes appear to change colour with the lighting? This is because the iris has two layers. Sometimes there is pigment in both layers. In people with blue or green eyes, the front layer will have little melanin. Depending on how much external light there is, eyes may appear to change colour as it hits each layer.

Changes in light can also affect the size of the pupil; it enlarges in dimmer lighting and grows smaller in brighter lighting. When the pupil size changes, the pigments in the iris compress or spread apart which can appear to slightly change the eye colour. Strong emotions can also change the pupil size, for example when people are in love or feel angry, this can also affect the iris colour.

Eye colour also can change as we age

In a small number of people, eye colour also can change as we age, especially for those who have lighter eye colours. Exposure to sun can make your eyes turn darker, just as your skin changes colour under the influence of sun rays. Be sure to protect your eyes with sunglasses paired with lenses including a UV filter, like everclear UV, if you're spending lots of time outdoors.

Of course, if you really don't like your eye colour and want to try something different you can always wear coloured contact lenses which are designed to imitate the appearance of your iris. They can alter the appearance of your natural eye colour, either with subtle enhancement - FreshLook Dimensions or something more dramatic - FreshLook Colorblends.

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