Eye Colour Is More Unique Than Your Fingerprint

Did you know your eye colour is unique - just like you!

While it is possible that you may share blue eyes with your immediate family, how that colour appears in your eyes is unique to you. With the development of modern technology, many biometric systems (i.e. using biological traits for identification purposes) are now designed on the basis of a unique iris since no two people possess the same iris patterns.

In the most simplified versions of eye-colour prediction charts, both blue and green eyes are considered to be recessive, brown eyes are considered dominant over all other colours and green eyes are thought to be dominant over blues eyes. Although these concepts are generally accurate, the genetics of how eye colours are determined is actually far more complicated than what we previously thought. Despite what high school science classes taught us, human eye colour is dependent upon a variation of several different genes and the complex interaction between them.

You cannot simply determine what colour a baby’s eyes will be by calculating the various probabilities using a punnet square. If you belong to a family with a long line of brown-eyed individuals over multiple generations but end up with green or blue eyes…don’t panic, it doesn’t mean you were secretly adopted! Despite the popular belief that two blue-eyed parents cannot have a brown-eyed child, this out-dated concept and other similar eye-colour myths have been proven unreliable.

With more recent studies in genetics, it is now understood that one’s eye colour depends on the amount of pigment (melanin) found in the iris and how it is distributed. Genetics determines how much melanin is present in the iris of your eye. Though there are two main genes that have the most influence, up to 16 different genes play a role in determining eye colour.

Want to know what causes your eye colour?

Blue

If you have blue eyes this means you have little or no melanin in the front layer of your iris. When light goes through the eye, it hits the back of the iris and reflects out. As the light goes through the stroma (the upper layer of the iris), the presence of proteins causes blue light to scatter, which causes the iris to appear blue.

Brown

People with brown eyes have a large amount of melanin present in the stroma of the iris which absorbs more light, reducing the amount of light being reflected.

Green

Green eyes contain a melanin concentration in-between blue and brown. If you have green eyes, this means that the front layer of your iris has only a small amount of melanin (more pigment that blue eyes but less than brown eyes) which tends to be the red or yellowish pheomelanin. Given that the melanin concentration is low, the light scattering effect creates a blue colour, which mixes with the yellowish colour of pheomelanin, making the eye appear green.

Hazel

Similar to green eyes, hazel eyes have less melanin than brown eyes, but more than blue eyes. Hazel eyes are caused by a blend of Rayleigh scattering of reflected light and a moderate amount of melanin in the iris’ anterior border layer (a layer of dense pigmented cells within the iris).

Red and Violet

True violet or red-coloured eyes do not occur naturally in humans. However, due to the extremely low quantities of melanin, people with severe forms of albinism eyes may appear red under certain lighting conditions, allowing the blood vessels to show through. When very bright light from a camera flash reflects off the retina, this causes the pupil to appear red in the photograph which is commonly called the “red-eye effect”. Even though the deep blue of some people’s eyes appears violet at certain times under different lighting conditions, only people with albinism are the only exception for presenting “true” violet-coloured eyes.

Can eye colour change?

Most European descent babies have light coloured eyes after birth, which can change in the first couple of years. As the child develops, melanocyte cells (found within the iris of the of the human eyes) continually produce pigment and therefore the babies’ eye colour can often change. A child’s eye colour is usually established between 3 and 6 months of age, in which after this period, the human iris colour will most likely remain the same throughout adulthood unless the colour appearance is altered through the use of makeup, lighting and colour contacts.

Although most people’s eye colour remains constant throughout their lifetime, sometimes chemical reactions and hormonal changes within the body can result in changes (lightening or darkening) of the iris during childhood, puberty, pregnancy and sometimes after serious trauma. However, if you notice a change in colour of the whites of your eyes, this yellowing is a pingeculum and may be an indication of liver disease.

No matter what colour your eyes are, they are distinctive to you. Because our eyes are so unique, regardless of your age or physical health, it is important to take care of them by booking an annual eye exam. A comprehensive eye exam with Auckland Eye will help to detect any eye problems at their early stages when they are the most treatable to help preserve your vision for life!

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