Explaining Eye Color: Why You Should Love Your Brown Eyes
You’ve heard it a million times before or read it as a caption under someone’s selfie: ‘’Eyes are the window to the soul’’. As humans, we find eyes very important, right? The eyes are probably the first thing you notice when you meet someone for the first time. The iris, the part of the eye that gives an eye it’s color, can be brown, amber, hazel, blue, green, grey, blue with brown/yellow around the pupil and more. That’s why the name ‘Iris’ is well chosen considering it means rainbow in Greek. But how is it that we know so little about what actually causes some irises to be dark and others to be light? Well, my name is Mark, I’m a biology student from The Netherlands (so sorry if my grammar is a little bad at times) and I’m here to tell you a little more about it.
My eyes are light blue like my mom, while my sister has dark brown eyes like my dad. A week ago we were sitting on the couch and she was on her phone on Instagram. She was liking pictures of girls she follows on there. Social media apps like Instagram are a great place for people to post their selfies and show off their beautiful eyes. After a while of scrolling through the pictures she sighed and said: ‘’Look at how beautiful the eyes of these girls are. So bright. I wish mine were blue or green. It’s unfair that I got dad’s boring eyes and you didn't.’’ She seemed really down about it. So, for her and all other brown eyed people who feel bad about their eye color:
I hope that after reading this, you’ll find out there’s nothing to be sad about.
Let’s start off by saying: there are NO blue or green pigments in the human eye. The only pigmentation that occurs in the human eye has the color brown. This brown color can vary from light brown (yellowish) to black. So… how come there are blue, green and other colored eyes? To answer that we have to talk about the way the iris is build. To make this article less complicated I’m only going to talk about the two parts that are relevant when talking about eye color. The iris has a back part, called the epithelium, which is black due to high levels of pigment. Everyone has pigment in this layer except people with albinism. And there’s a front part called the iris stroma. Eye color depends on the amount of pigment (melanin) in the stroma of the iris. Dark brown eyes have the most pigment, green eyes have less pigment and blue eyes have little to no pigment in the stroma.
Picture from http://genetics.thetech.org/ask/ask176. This shows the relation between melanin levels in the iris and the eye color.
People with BLUE eyes don't have blue pigmentation in their eyes. Blue eyes lack the dark pigmentation in their stroma that brown eyes have. The melanocytes (pigment producing cells in the eyes) don’t produce melanin in this part of the iris. Because the stroma is clear it allows the light that travels through the eye to be absorbed by the dark epithelium. However the epithelium only absorbs the colors with longer wavelengths (red, orange, yellow, green) and not the shorter wavelengths (blue, violet).
These are all the color that white light contains. White light comes from sources like the sun and lamps.
The blue color is reflected and scattered by the hazy fluid in the stroma which gives the appearance of a blue eye (this is called Rayleigh Scattering). A similar thing happens to the sky: the shorter wavelengths are scattered by the particles in the air making it appear blue.
So what you see when looking at blue eyes is the light (from the sun, or another source like a lamp) that couldn’t be absorbed by the eye. This means eye color in those with blue eyes is structural; it doesn’t come from the eye itself, it depends on external light that reacts with the particles in the fluid of the stroma. This is also why blue eyes can appear a different color or darker when the light source changes (rainy weather, sunset). What a person is wearing can also affect the perceived color.
People with BROWN eyes have a lot of pigment in their iris stroma. Especially the ones with eyes so dark they almost seem black. This pigment covers the iris and absorbs the longer AND the shorter wavelengths. The color you see isn’t a structural color, it’s the color of the pigment (melanin) that’s in the iris. The melanocytes in brown eyes are active and produce lots of melanin to fill the stroma with. The layer of pigment in dark eyes is what prevents the light from being scattered and reflected by the fluid in the iris stoma.
GREEN eyes are a combination of pigment and scattering/reflecting of light. There’s less pigment than brown eyes and more pigment than blue eyes in the stroma. The combination of this light brown melanin and the blue light that’s scattered makes it appear green. This green color, like blue, is an illusion because there’s no green pigment in the human eye. It is also a structural color and can change depending on light sources.
Hazel eyes are also a combination of scattering and a moderate amount of pigment in the iris stroma. Most hazel eyes are multi colored because they have a higher concentration of pigment around the pupil making it brown while the outer part of the iris has a lower concentration making it look green. Hazel eyes are known for changing color the most. Sometimes they can look brown/gold or completely green.
Grey eyes have even less pigment that blue ones. They do have the dark epithelium at the back of the iris but the iris stroma is completely clear. The difference between grey and blue eyes is still up for debate. There’s a theory that the collagen in the stroma is structured differently in grey eyes making the light go through a different kind of scattering (Mie scattering).
Amber eyes have more of the light brown (yellow) pigment in the iris and a smaller amount of the dark brown pigment. This makes them look orange copper/gold.
Heterochromia (different colored eyes)
Sometimes people have irises that have multiple colors in them or two completely different colored eyes. This can be explained due to differences in the presence of melanin in these irises. Where there's more melanin the iris will be darker, where there's less it will appear lighter. Examples of this:
Heterochromia iridum (sectoral heterochromia)
Baseball pitcher Max Scherzer has heterochromia
It’s a really interesting thing and if you want to know more you can easily search for more information on this condition on the Internet.
Genetics
The genetics of eye color are more complicated that we were taught in school. It is still generally accepted that brown eyes are dominant. However saying that blue eyes are simply recessive genes is proven to be incorrect. This article focuses on what eye color is and not on the genes that are involved with having a certain color. So if you want to know more about the genetic side I suggest you pay a visit to this site:
http://genetics.thetech.org/genetic-categories/eye-color?page=1
Here actual geneticists answer questions about the genetics of eye color.
Dear brown eyed people
I hope that by know you understand why it isn’t necessary to dislike your brown eyes. Your eyes are structured the same as light colored eyes, you just have something extra that covers your irises: lots of pigment. The pigment producing cells (melanocytes) in your eyes are very active. If the layer of brown pigment in your eye would be removed, you would have the same light (blue if everything is removed, green if some of it is removed) colored eyes as others who naturally have them. There’s actually a new type of surgery being developed to do this. It will turn brown eyes blue. The following thing is said about this:
Link: http://www.dailymail.co.uk/femail/article-2074243/New-laser-surgery-turns-brown-eyes-blue-critics-say-reckless-vanity.html
Some babies (particularly Caucasian babies) are born with blue eyes that change to brown over time. This is because it takes some time for the melanocytes to start producing pigment. They either start producing a lot and become brown, they produce a moderate amount and become green/hazel or they don’t produce pigment at all which makes them stay blue. Even though babies of other races (Asian, black) are often born with dark brown eyes; their eyes aren’t structured differently. The difference between their eyes and light eyes are also the layer of pigment. It just means their melanocytes were already active before birth. A surgery to remove the brown pigment layer would also result in light colored eyes for people of Asian or Black descent.
Though these type of surgeries will very likely become available in the near future, I would like to tell brown eyed people not to do it. First of all: it’s never a good idea to let someone put a laser in your eye to destroy the pigment just for cosmetic reasons because of the possible complications. And second of all: brown eyes are beautiful. I find dark eyes very soulful and brown is the only eye color that isn’t an illusion (remember: there are no blue or green pigments in the human eye, the light color you see is an illusion caused by light reacting with the stroma of the iris. Whereas the pigments humans can produce in their irises are actually brown themselves).
To all the brown eyed people who dislike their eyecolor: I want you to look into a mirror and realize that there’s a layer of brown pigment that covers your eyes, and that underneath them there’s the same structures that would allow your eyes to be light colored. Without this layer your eyes would also appear blue or green. Not having light eyes doesn’t mean you lack something; it means you have something extra. How cool is it that your eyes can absorb all the colors that come from light sources such as the sun? How cool is it that your eye color doesn’t depend on external circumstances but is produced by your own cells? It’s very cool.
People often tell those with light colored eyes that they’re lucky or blessed. I’m here to tell brown eyed people that they’re also lucky and blessed. Just because brown eyes are the most common eye color in the world doesn’t make them boring. I mean: when something is perfect, all that’s left to do is to replicate it.
''If eyes are the window to the soul then at least the brown-eyed window of your soul is not a reflection of something else but rather something made by your body itself.''
If you have any questions about this article or want to know more about what eye color is, send an email to [email protected] Mark will answer your questions as quickly as he can.
If you want to know more about the genetics of eye color, go to http://genetics.thetech.org/genetic-categories/eye-color?page=1 where you can ask a geneticist a question about it or look through their already answered questions (there are many!).
Sources/read more:
http://en.wikipedia.org/wiki/Eye_color
http://en.wikipedia.org/wiki/Iris_pigment_epithelium
http://en.wikipedia.org/wiki/Iris_(anatomy)
http://en.wikipedia.org/wiki/Structural_coloration
http://en.wikipedia.org/wiki/Turbidity
http://en.wikipedia.org/wiki/Rayleigh_scattering
http://genetics.thetech.org/original_news/news39
http://genetics.thetech.org/ask/ask176
http://www.dailymail.co.uk/femail/article-2074243/New-laser-surgery-turns-brown-eyes-blue-critics-say-reckless-vanity.html
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