I’m pretty sure we all know someone who’s just a little bit too excited about their own eye colour. My sister makes owl-like eye contact with camera lenses to show off those cornflower-blue, Cillian Murphy-esque peepers.
I’ve been known to casually mention how rare my own green eyes are. I understand it is annoying. I still cannot help it. But if you’ve got grey eyes, it turns out that there actually is some serious magic going on with your peepers.
Recently, Dr. Karan Raj, a doctor who debunks medical myths on TikTok, shared a video about the topic. “People who have grey eyes have the craziest physics going on in there,” he began the video.
Here’s the science behind grey eyes:
Grey eyes are grey for the exact same reason a cloudy sky is grey
Sure, it might all feel very 2014 Tumblr to describe grey eyes as stormy. But Dr. Raj points out that there’s actually some truth to the teen-esque turn of phrase.
He points out that for grey eyes, the iris (or coloured ring around the pupil), has a layer of cells called the stroma. “Similar to those with blue eyes, the grey-eyed folks have little to no melanin pigment in the stroma of the iris,” the doctor says.
In blue eyes, the shortest wavelength of light ― which just so happens to be blue ― scatter the most across the stroma, giving them their icy appearance. Dr. Raj explained that this is similar to something called Rayleigh scattering, which makes the sky look blue.
I was expecting grey eyes to follow a similar formula; whatever way the stroma interacts with light determines its colour. Respectfully, whoopty-effing-doo. But no; Dr. Raj shared that grey eyes have more collagen in the stroma than blue eyes (while sharing a similar lack of melanin).
“This means there’s a more even scattering of all the lights that’s not frequency-dependant,” he adds. This is similar to a grey, cloudy sky, because when light hits the water droplets, all the wavelengths are scattered equally. Except, instead of water droplets, there are collagen deposits.
“The colour has nothing to do with pigment,” Dr.Raj finishes. Unlike with green, brown, or blue eyes, grey eyes’ colouration comes from their structure alone (OK, OK, that is pretty cool).
That means grey eyes can change colour
Yes, those people in school who swore up and down that their eyes changed colour according to their mood might have been a little irritating. But if they’ve got grey eyes, there might have been a kernel of truth behind the claim.
While your temper might not affect your eye’s hue, if you have grey eyes, thelight might. Due to the structural colouration of the stroma (or the fact that it doesn’t rely on pigment for its hue), “the eye actually can change colour, depending on the position and intensity of the light,” Dr. Raj shared.
Here’s the entire video: