But not this week. This week I thought "I know, this is an easy, goodey. No effort, and certain to please. This one is perfect - elegant, suprising, simple". Exactly what the doctor ordered (pun intended)
But then I made a mistake. I thought I would check something. Dot a couple of Ts, cross a couple of Is.
And indeed it did.
So this weeks Factoid is hopefuly one of two parts. The first is the simple, elegant, "I have found and checked the story" part.
The second will be the "Here's the last part you were curious about" that "I haven't yet found the facts for".
So what am Eye wittering about? What is this pre-disclaimered factoid?
Why do some have blue, grey, hazel, green, brown or black eyes?
What is going on?
Today I am going to talk just about Blue and Brown
Easy
Makey-Sensey.
We make a dark brown pigment called eumelanin (those of you who read the blog when it was an email not a website may recall me writing about this in relation to fossilised penguins).
In the iris of our eyes, there are two layers - and in both layers there are melanocytes - cells which make melanin (both eumelanin and its reddish cousin, pheomelanin). This melanin is stored in organelles called melanosomes.
As I said, easy.
So what about us with blue eyes? Do we have a blue melanin? NO! We have dark brown eumelanin too. In fact the iris pigment epithelium has just as much eumelanin than our brown eyed friends. Even the front stroma has dark brown eumelanin in it, But only a very little. Just a smidge, just a smattering. Just SCATTERING! . |
SCATTERING light? What's that? Think back to your year 9 lessons and look at the sky.
Particles of dust (and even molecules) in the sky cause sunlight to scatter, with the shorter (bluer) wavelengths scattering more and bouncing towards us from all directions - this is what makes the sky blue!
Blue eyed friends do the same - the small amount of eumelanin in their irises (correct plural is irides I believe) scatters the blue parts of white light too, causing some of it to come back at us and making the eye blue. The other colours of light - keep on going through the stroma to be absorbed by the brown iris pigment epithelium layer at the back of the iris.