Arshad had brown eyes as did all his family members and most people around him. For a long time, he thought that everybody had brown eyes, some dark and some light. Then a new student, Oliver, joined the school; his parents had come to Pakistan

from America. Besides his fair complexion and light hair, what interested Arshad was his blue eyes. He had seen fair complexion and light hair in English movies and other TV programmes, but had never paid attention to eyes, as at his age he was more interested in action than in such details.

It intrigued Arshad more when he learned that all of Oliver’s family members had blue eyes. Oliver told his new friends that many people in his country had blue eyes.

Arshad started to pay attention to people’s eyes and soon discovered that many people had eyes of different colours — brown, black, grey, hazel, green, etc. He decided to ask his science teacher to explain it, and in the next class asked her the reason why different people have different coloured eyes.

The science teacher, Miss Sarwat, thought it was a very intelligent question and promised to explain the issue in the next class, as she realised that most students were puzzled with the idea.

Miss Sarwat told the class that not everyone has eyes of the same colour and that eye colours vary from brown, blue, grey, green, hazel, etc. depending on various factors. She explained that the coloured part of the eye is called iris (a muscle that expands and contracts to control pupil size), which has pigments that determine the eye colour.

The colour of the eye depends on two pigments: melanin (brown pigment) and lipochrome (yellow pigment); it also depends on how the iris scatters light. Light-blue eyes mean that melanin or brown pigmentation is absent, while those with dark brown eyes have an abundance of melanin.

It was believed that the eye colour was the result of a single genetic trait passed on to children from their parents, and every individual received one eye colour gene from each parent and the gene that was dominant determined the child’s eye colour. Since the darker colour tends to dominate, brown was always considered to be dominant over blue, i.e., if one parent had brown and the other blue eyes, the child would have brown eyes (though it is not necessarily true), and only if both the parents had blue eyes then the child would have blue eyes.

While it is true that the parents’ genetic makeup determines the amount of pigment, or melanin, in the iris of their child’s eye, variations can result in different shades or even a totally different colour. For instance, though it is most likely that if both parents have brown eyes their children will also have brown eyes, children can have a different eye colour than their parents — blue, hazel or grey, etc.

We will not go here in the genetics of eye colour as it is very complicated, and a lot is still not known about the specific genes that determine a person’s eye colour. However, it is sufficient to know is that eye colour is determined by many different gene combinations.

We all know that the iris controls the pupil size, which enlarges in dim light and shrinks in brighter light, or when we focus on nearby objects. When the pupil size changes, the pigments in the iris compress or spread apart, changing the eye colour a bit. Certain emotions also can change both pupil size and iris colour. That’s why some people’s eyes seem to change colours when they’re angry or loving.

While majority of people have both eyes of the same colour, some have eyes that are of different colour. Usually this condition — called heterochromia — is caused by faulty developmental pigment transport, local trauma either before or shortly after birth or a benign genetic disorder.

Now let’s learn some facts about the various eye colours there are.

Brown eyes

The colour brown is due to a high concentration of melanin in the iris, causing more light to be absorbed and less light to be reflected. Because of this, brown eyes are more naturally protected from the sun.

It is believed that originally all humans had brown eyes but due to genetic mutations, other colours came about. Perhaps this is why brown is the most common eye colour, and over half of the people in the world have brown eyes.

Brown eyes are common in Europe, East Asia, Southeast Asia, Central Asia, South Asia, West Asia, Oceania, Africa and the Americas. Light or medium brown eyes are also common in South Europe, the Americas, as well as the Middle East and South Asia.

Blue eyes

Those who have blue eyes have low concentrations of brown melanin, due to which more light is allowed to reflect to wavelengths on the blue colour spectrum, which in turn make the eyes appear blue. Some eight to 10 percent of people worldwide have blue eyes.

According to recent research, everyone with blue eyes is related and have the same ancestors. Blue eyes are common in northern and eastern Europe, though some people in southern Europe, Central Asia, South Asia, North Africa and West Asia also have blue eyes.

Grey eyes

Like blue eyes, grey eyes have a dark epithelium at the back of the iris and a relatively clear stroma at the front. However, grey and blue eyes appear different because grey eyes have larger deposits of collagen in the stroma; it can also be due to a difference in the concentration of melanin at the front of the stroma.

Grey eyes may appear blue at first glance, but they tend to have flecks of gold and brown colour in the iris. They may appear to change colour from grey to blue to green, depending on clothing, lighting, and mood (which may change the size of the pupil, compressing the colours of the iris).

Grey eyes are the most common in Northern and Eastern Europe, though they are also seen in Northwest Africa, in the Middle East, Central Asia and South Asia.

Green eyes

Green is considered to be the least common eye colour in the world, though some consider amber to be even more unusual. Only about two percent of the world’s population has green eyes.

Green eyes are a genetic mutation that produces low levels of melanin, but more than blue eyes. The green eye colour is not only the result of pigmentation, but also because of the lack of melanin in the iris, more light scatters out, which make the eyes appear green. Green eyes contain the yellowish pigment lipochrome. Changes in light make lighter eyes look like they are changing colour like a chameleon.

Green eyes are common in Northern, Western and Central Europe as well as in Ireland and Scotland. Green eyes are most common among those of recent Celtic and Germanic ancestry.

Hazel eyes

Hazel eyes mostly consist of shades of brown and green, and are sometimes mistaken for green or brown eyes. They are not as rare as green eyes but are rarer than blue. Only about five percent of the population worldwide has hazel eyes. After brown eyes, they have the most melanin.

In hazel eyes, the light scatters as it does with blue and green eyes. Hazel eyes may also appear to change colour from green to light brown to gold, depending on the light. It is not known if hazel eyes developed from brown or green eyes.

Amber eyes

Amber eyes are of a solid colour and have a strong yellowish/golden and russet/coppery tint. As in green eyes, hazel eyes, too, have deposition of lipochrome (yellow pigment) in the iris.

Amber eyes should not be confused with hazel eyes; while amber eyes have a solid gold shade, hazel eyes may appear to change colour and consist of flecks and ripples. Even though amber is considered to be like gold, some people have russet or copper coloured amber eyes that is often mistaken for hazel.

Red and violet

Due to extremely low quantities of melanin, the eyes of people with severe forms of albinism may appear red under certain lighting conditions. Because there is so little melanin in the eyes, there is nothing to conceal the blood vessels hard at work. Although the deep blue eyes of some people can appear violet at certain times, true violet-coloured eyes occur only due to albinism.

Published in Dawn, Young World, February 13th, 2021