Rim around the iris

December 1, 2008 12:06 AM

Why do I have green eyes with blue rims? What causes the iris to be one color while the darker rim around it is another?

Out of curiosity, and not being well-versed in the sciences, I'm wondering how eyes of one color can have rims of a different color. For instance, I have green eyes with blue rims. Is this blue rim the corneal limbus I'm looking at? From a comment onthis mefi post: "The iris contains pigment granules. Density of granules is a determinant of eye color. Some people have especially dense concentrations of granules towards the periphery of the iris. This causes the dark iris 'ring'".
No source provided. Is this true? If so, how is the iris a different color? (I was under the impression that the genes involved in the expression of blue and green eyes are different.) Does this happen with other colors as well?
Looking through pictures on google, it seems many green eyes (in particular, the ones that tend toward yellow?) have the blue rim.

posted by Baethan to science & nature (4 comments total)

I have brown eyes with a green rim, so yes, it does happen with other colours. As to the rest of your questions, that comment you linked to is pretty accurate.
posted by tehloki at 12:48 AM on December 1, 2008 [1 favorite]

That rim is not the corneal limbus itself, which is above the iris, but the "limbal ring." I sure as heck can't tell you why the coloration is different there, but this page on creating authentic artificial eyeballs is amazingly detailed with regard to eye coloration and composition. I have a blue limbal ring, green eyes overall, a yellow ruff and thin sclera, apparently.
posted by Ambrosia Voyeur at 1:41 AM on December 1, 2008

Here's an overview of what's known about eye color genetics. There are a lot of genes involved.

The answer to your question is pretty complex. The best overview I found was this guide for painters of artificial eyes. The short answer, yes, it's probably the limbus - blue and green in eye colors are produced by various sorts of scattering - but it's hard to know without a picture of what you're referring to.
posted by ikkyu2 at 2:01 AM on December 1, 2008

I also technically have brown eyes with a green rim, except the rim is so broad that the overall impression is of green eyes. Oh, and the brown is light, sort of gold-ish. (Yes, i have weird eyes).

So, it happens in other eyes, with lots of variations.
posted by Kololo at 6:53 AM on December 1, 2008