Why Series: Why Do We have Different Eye Colors?

Eye color is a polygenic phenotypic character determined by these distinct factors: melanin and collagen deposits, and the frequency-dependence of the scattering of light by the turbid medium in the stroma of the iris.
The colour of your eyes depends on how much of the pigment melanin you have in your iris—the coloured part of your eyes, and how much melanin and collagen deposits you have in your stroma.
Shortly, the more pigment you have in your eyes, the darker they will be
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This means that green, blue and grey eyes are lighter because they have less “turbid medium in the eye”.

Why, and in which sense, the amount of melanin and collagen deposits determines the colour of an eye?

The fact here is that...your eyes aren't blue (or green) just because they contain pigmented cells. There is actually more physics involved here than you may think!
The eye colour is actually structural.
Our beautiful coloured part of the eye is called the iris, and it's made up of two layers. One is called “epithelium”, at the back of the eye, and the other is the “stroma”, at the front.
The epithelium is very very thin, (it is only two cells thick) and contains black-brown pigments.
Sometimes, you can notice some people have some dark specks in their eye.
It is, in fact, the epithelium peeking through.

The stroma is made up of colourless collagen fibres.
But it can also contain melanin.
Fascinatingly, the amount of collagen over the amount of melanin it's actually what controls our eye colour.

This is exactly how things work:
Brown eyes

Brown eyes are eyes rich in melanin in their stroma, containing a huge amount of it, which is able to absorb most of the light entering the eye regardless of collagen deposits, giving them their dark colour.
I often hear brown-eyed people complaining about their eye colour. Don't be silly! You got rich-melanin eyes! This should be included on your strengths list.

Green eyes
Green eyes don't have much melanin in them, but they also have no collagen deposits.
This means that, as in brown eyes, some of the light entering them is absorbed by the pigment.
But at the same time, the particles in the stroma scatter light as a result of something called the Tyndall effect, which creates a blue hue.
Combined with the brown melanin, this results in the eyes appearing green.
Last but not least, let's talk about blue eyes.
People with blue eyes have a completely colourless stroma.
There is no pigment at all in it, and it also contains no excess collagen deposits.
This means that, while brown and green eyes absorb light, all the light that enters in a blue eye is scattered back into the atmosphere and, as a result of the Tyndall effect, creates a blue hue.

This is interesting because it means that blue eyes aren't always “that blue”.
It actually depends on the amount of light available when you look at them!
We know all of this is just mind-blowing!
Could you imagine that your eye colour actually depends on melanin, collagen and their response to light? Could you imagine that all of this is regulated by the laws of physics?

Ok, but as we've seen, the scattering of light, when it happens, is kinda directed toward blue. It's like he has a preferred colour (or, as scientists would say, a preferred wavelength).

Why?
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Credits: Ron Miller
Credits: Nasa/Shutterstock/Storyblocks/Elon Musk/SpaceX/ESA/ESO
Credits: Flickr

Video Chapters:
00:00 Introduction
00:56 Physics Behind Eye Color
01:47 Explanation
03:28 Blue Eye Color
04:39 Rayleigh Scattering

#insanecuriosity #eyecolor #rayleighscattering

[InsaneCuriosity]

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[EdithCasines]

My father had blue gray eyes! My mother had a medium brown eyes! My eyes are hazel! And sometimes in the ocean! My eyes look green with a speck of gold in it! When I take photos indoors, my eyes appear to be light brown! But when I take photos in front of the sun! My Isa caramel with a touch of green!

[judyoung]

I like this video. All too often we FALL in Love because of the eyes of a girl ! Further, how much sadness and pain we carry all our life because, for some reason, we could not marry those beautiful eyes !

[judyoung]

All eyes are beautiful. I love eyes that express " Kindness, Love, tenderness etc. " I think that Shakespear once said that " The eyes is the Window of the Soul ! " indeed !

[MothersLovingArmsNursery]

Have you seen butterfly wings under a microscope? The colors are ALL light reflection, Gods genus, just pure perfection.

[MG-erdm]

1st: First to say how thrilled l am to hear of lnsane Curiosity's new "WHY SERIES" !!! ❤

[bodhiwan]

I was actually pretty curious about why the sky isn’t red or any other colour but blue so this really cleared things up thanks.

[deborahjett]

I have beautiful and very green eyes outlined by a teal blue ring.
The green from my mother and
the blue from my father.
I wonder if this combination
is rarer even from typical green eyes.👁

[johnnyj]

I got most of the way through this and realized I didn't understand hardly any of it.

[insanecuriosity]

Hi guys, do you like this “why series”? Is there anything more you want to hear?

[davidmacphee]

Umm .... I think I like brown eyes the best but I love the diversity as I'm an artist. You can see clips of Barbara Eden here, if you know who she is, Check out the ways she "ACTS" with her eyes. She is so funny!

[lynnbarker]

I have blue eyes. But will change to grey when I am saddened

[bbygrl]

My eyes are blue with a green ring around the blue. Seems my mood change the color or the color of clothing in wearing make them look either more blue or green. They also look more green when I'm mad or feeling upset, blue when happy or feeling ornery. 😆

[kzd]

🙏Very interesting—Eyes are the window of the souls— 🙇‍♀️🙏👏👏👏

[infinitumneo]

Deep in Earth's ancient past there was more oxygen in our atmosphere resulting in more purple light scattering. The data came from ice core drilling. This would have been the time of the dinosaurs.

[pellehyltoft]

:-) simply genius! (-:
:-) great work! (-:

[MothersLovingArmsNursery]

We look differently because God LOVES diversity. He loves all of us no matter what we look like and we are supposed to do the same. Love each other we are all simply human. Stop trying to explain everything away, just admire the beauty.

[allisonerbach]

Do my change color because of less pigment and something else is missing?

[allisonerbach]

Wait stigma was supposed to be a sign of dark spots. I feel confused now.

[whimbrella]

how do genetics play into eye colour? i have green but my mum has blue and my dad has brown