What do you know about different eye colors?
The colored part of each eye is the iris of the eye. The iris is colored; Because its fibers contain pigments to protect it from light damage. Most pigments are concentrated in the back of the iris and there is not much pigment in the front. For this reason, the front of the iris is very transparent and colorless.
Light waves absorb some colors as light passes through; Therefore, the reflection of light in the pigments causes the iris to look “colored”. Eye color reflects pigments that have accumulated on the back of the iris.
If the pigments do not increase in the front of the iris, the eye will be blue for the rest of its life; But if they are large and spread on the front, they will turn brown. The so-called those with double eyes are called heterochromatic.
Genetic Cause in Eye Color Differences
Eye color is an inherited trait that is affected by more than one gene. These genes are used for communication for minor changes in genes and neighboring genes. These changes are known as single nucleotide polymorphisms, or SNPs. The exact number of genes that contribute to eye color is currently unknown, but there are few possible candidates. A study in Rotterdam (2009) showed that using only six SNPs, eye color could be predicted to be more than 90% accurate for brown and blue. There is evidence that 16 different genes may be responsible for eye color in humans. However, the two main genes associated with eye discoloration are OCA2 and HERC2, both of which are located on chromosome 15.
Change in Eye Colors
Most newborns of European descent have brightly colored eyes. As the baby grows, melanocytes (cells in the iris of the human eye, as well as skin and hair follicles) slowly begin to produce melanin. Because melanocyte cells are constantly producing pigment, the color of the eye can theoretically be changed. People’s eye color usually develops between 3 and 6 months of age, although this can happen later. Viewing a baby’s iris from the side using only light transmitted and without reflection from the back of the iris, the presence or absence of small amounts of melanin can be used. The iris, which appears blue in this method of observation, is more likely to turn blue at infancy. The iris, which appears to be golden, contains some melanin, even at this young age, and may change from blue to green or brown in infancy.
Different Eye Colors
Amber eyes have a strong color and have a golden yellow and copper color. This may be due to the deposition of a yellow pigment called lipochrome in the iris, which is also found in green eyes. Amber eyes should not be confused with honey eyes. Although honey eyes may contain elements of amber or gold, they usually include other colors such as green, brown, and orange.
Also, honey eyes seem to change color and are streaked and variable, while amber eyes have a solid golden color. Although amber is considered golden, some people have amber or copper-colored eyes, which many people confuse with honey eyes, although hazelnut color seems more dull and, as mentioned above, contains green with red / gold stacks. Amber eyes may also contain light gray-gold.
There are no blue pigments in the iris or eye fluid. An autopsy shows that the iris pigment epithelium is black-brown due to the presence of melanin. Unlike brown eyes, blue eyes have a low concentration of melanin in the iris stroma, which is located in front of the dark epithelium. Wavelengths longer than light are absorbed by the dark underlying epithelium, while shorter wavelengths are reflected and subjected to Rayleigh scattering in the turbulent environment of the stroma. This is the scattering frequency dependence that makes up the blue appearance of the sky.
In humans, brown eyes are caused by a relatively high concentration of melanin in the iris stroma, which causes light to be absorbed at both shorter and longer wavelengths.
Dark brown eyes are predominant in humans, and in many parts of the world there is almost only iris color. Dark brown pigment is common in Europe, East Asia, Southeast Asia, Central Asia, South Asia, West Asia, Oceania, Africa and the Americas. Most people in the world generally have brown eyes or dark brown eyes.
Light brown or medium-colored eyes are also commonly found in southern Europe, between the Americas and parts of Central Asia (Middle East and South Asia).
There are no green pigments in green eyes. Like the color of blue eyes, it is a light illusion. Its appearance is created by the combination of brown or amber colors of the stroma, which is given by a low or medium concentration of melanin, and its blue color is transmitted by the scattering of light reflected by Rayleigh. Green eyes are more common in northern and central Europe. They are also found in Southern Europe, Western Asia, Central Asia and South Asia. In Iceland, 89% of women and 87% of men have blue or green eyes. A study of Icelandic and Dutch adults found that green eyes were much more common in women than men.
Like blue eyes, gray eyes have a dark epithelium on the back of the iris and a relatively clear stroma on the front. One possible explanation for the difference in appearance between gray and blue eyes is that gray eyes have more deposition of collagen in the stroma, so that the light reflected from the epithelium is scattered by Mie (which is not strongly frequency-dependent). From rail scattering (where the shorter wavelength is scattered more than light). This could be similar to a change in the color of the sky, from blue, which is illuminated by rail scattering of sunlight by small molecules of gas in the sky, to gray due to the scattering of large droplets of water when the sky is cloudy. On the other hand, it has been suggested that gray and blue eyes may differ in melanin concentration in front of the stroma.
Honey eyes are due to a combination of rail scattering and a moderate amount of melanin in the anterior border layer of the iris. The color of honey or hazel eyes often appears to change from brown to green. Although hazelnuts are mostly brown and green, the predominant color in the eyes can be brown / gold or green. In this way, many people confuse hazelnut eyes with amber and vice versa. This can sometimes cause the iris to become very colored, meaning the eye is light brown / amber near the pupil and charcoal or dark green on the outside of the iris (or vice versa) when exposed to sunlight.
The eyes of people with severe forms of albinism, due to the presence of very low amounts of melanin, may appear red under certain conditions, allowing blood vessels to appear through it. In addition, flash photography can sometimes cause a “red eye effect,” in which very bright light from the flash opens the retina, which is abundantly vascular, causing the pupil to turn red in the photo. Although the deep blue eyes of some people, such as Elizabeth Taylor, may sometimes appear purple, “real” purple eyes occur only because of albinism.
Heterochromia (eye discoloration) – in which a person has more than one eye color – affects less than 1% of people.
The two eyes may be completely different, or one part of the iris may be different.
AAO explains that in people with central heterochromia, the iris has two rings of different colors, while in people with complete heterochromia, the iris is one of the other colors.
Differences in Vision in Different Eye Colors
Under the same environmental conditions, there may be disagreement over the color of an object between two different people, and the factor that causes this disagreement is pigments called melanin, which are the main factors in determining eye color. The higher the amount of these pigments in the iris and the denser their texture, the darker the color of a person’s eyes; The same melanin concentration also depends on many factors such as hereditary, environmental, and other factors. The most important role of eye melanin is to protect the eye from the harmful rays of the sun.
People with bright eyes (honey, blue or green) have less sun protection than other people. Therefore, they need to protect their eyes from the sun more than other people.  The human eye consists of two types of light and color receptors in the retina.
Cylindrical cells are the photoreceptors of the eye that have a black and white vision and, depending on the amount of light received from the environment, determine the amount of darkness and brightness of objects. The number of cylindrical cells is more than the number of color receptors and reaches about 120 million; Cone cells, which are smaller in number than light receptors, have color vision and are divided into three distinct categories, each of which recognizes one of the colors blue, red, and green, allowing the individual to distinguish colors.
When a person is exposed to sunlight, the rays of the sun hit a part of the back of the eye called the yellow spot. The cylindrical cells receive these rays, make a neural message from them, and send them to the occipital region of the brain, where they are examined and answered if necessary. At this time, a large amount of ultraviolet light is received by the eye and destroys parts of the light receptors.
Because people with bright eyes have less melanin in their eyes than people with dark eyes, the lack of this protective factor means that their eye’s light receptors are more damaged and destroyed than other people. This difference in the number of light receptors in the eyes of different people causes a difference in the amount of light they receive from the environment; That’s why people with bright eyes see colors a little darker than others; But this amount is so small that it is not very visible in everyday life and only appears as a slight difference of opinion between people with different eye colors.
Health Problems that Can Affect Eye Color
People can develop heterochromia at any stage of their lives. Possible reasons for this are:
- Eye injury
- Swelling due to irite or uveitis
- Fuchs heterochromic cyclicity
- Horner syndrome
- Eye melanosis
- Iris tumor
- Posner-Schlossmann syndrome
- Chediak-Higashi Syndrome
Anyone who notices discoloration in one or both eyes should see a doctor.
Does Eye Color Affect Pain Experience?
A 2011 study found that women with light eyes, such as blue or green, had less labor pains than women with dark eyes, such as hazelnuts or browns. They also had less depression, negative thoughts and anxiety.
However, another study from a reputable source showed that eye color did not differ in the amount of pain women experience during dental work.