Tuesday, December 20, 2011

Heterochromia: Types and Causes

This woman has heterochromia,with one brown eye and one hazel eye.
Complete heterochromia
I introduced heterochromia recently by discussing its presence in dogs. Now, I will be going over it in a bit more detail, especially its existence in humans. Specifically, I speak of heterochromia iridis (also known as heterochromia iridum), which refers to the coloring of the iris of the eyes. Technically, heterochromia (or "different color") may refer to other parts of the body as well, such as hair, fur, or skin.

There are multiple ways in which heterochromia can be classified (and the classification I give here may be revised in the near future). There is complete heterochromia, where each eye is fully of one color. So, for example, one eye is blue and the other is brown or one eye is amber and the other green, among numerous other possibilities. This can be either inherited or acquired, with the acquired form having numerous different causes.

Sectoral heterochromia
Central heterochromia in my own eye
There is also incomplete heterochromia, where the difference in eye color is not so distinctly defined. Incomplete heterochromia can further be broken down into types. The two types are central and sectoral. Central is where the iris has a central ring that is differently colored than the rest of the eye, such as a brown ring in an otherwise green eye. Sectoral heterochromia, on the other hand, is where a section of the eye is a different color than the rest, with no rhyme or reason to the placement, such as a brown flash in an otherwise blue eye. Again, incomplete heterochromia has a number of possible causes.

Causes are incredibly varied when it comes to heterochromia. When the condition is present from birth (congenital), it is overwhelmingly likely that it is an inherited trait in some form or another. Any of the types of heterochromia can be congenital. Sometimes the inheritance is obvious (such as another family member having the same trait), but other times it is not. Familial heterochromia (there the trait is inherited and runs in a family) is a rather common explanation. Others are partial albinism (complete absence of pigment in a small area of the body), piebalding (a form of dominant lack of pigment sometimes seen in humans), and the potential for congenital heterochromia to be caused by mosaicism (mutation) or chimerism (fusion of twins early in development).

I suspect Jen's dark spots are from injury
Heterochromia can also be acquired, with the possible causes being quite numerous. One possibility is injury. Injury to the eye can case numerous types of alterations, including heterochromia. Blood vessels in the iris can leak or hemorrhage after trauma, causing potential for a permanent change in eye color. Central heterochromia can be a sign of high levels of toxins in the body.  Numerous medical conditions can also lead to a partial or complete change in eye color, such as glaucoma (sometimes through the medications prescribed for treatment), neurofibromitosis, eye inflammation, foreign bodies, and numerous other conditions and syndromes. Some of the syndromes have other symptoms which are far more important than heterochromia, as they can be far more dangerous.

A cat with complete heterochromia
Many animals commonly will have heterochromia, while the condition is unusual in humans. Horses, cats, and dogs all have relatively high incidences of heterochromia, generally in combination with a certain color phenotype. As I mentioned in my previous post, dogs will have the condition most often in combination with the merle or white spotting genes, but also can have the color inherited independently. Cats that are mostly white (through the white spotting gene) or completely white (through the dominant white gene) are usually the only ones that will be seen with heterochromia, but this is not always the case. In horses, heterochromia is most commonly associated with pinto markings. Certain other animals, such as cattle, are also know to exhibit heterochromia.

EDIT: I forgot to add to this in. There are numerous celebrities nowadays who have heterochromia. Some are more famous than others, but all have fascinating eyes. Mila Kunis, Christopher Walken, Kate Bosworth, Dan Akyroyd, Max Scherzer and Jane Seymour all have heterochromia of various types, just to name a few. David Bowie is thought by some to have heterochromia, but in fact has a permanently dilated pupil.

Sources are Right Diagnosis, Sewanee University of the South, PubMed Central from the National Center for Biotechnology Information, Miles Research, h2g2, University of Maryland Medical Center, Indian Journal of Ophthalmology, and Wikipedia. Images except for my eye and Jen's eye are from Wikimedia Commons under Creative Commons licenses: one, two, three (mine), four, five (mine), six.

26 comments:

  1. cool, but WHY does it do that????????????????????????????????????????????????????????????????????????????????????????????????????????????

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  2. why is my comment looking so weird??

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  3. I have sectoral heterochromia and I REALLY wish it was complete! :)

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    1. Me too! Mine is central heterochromia. How cool would that be if it was complete...

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    2. I don't know about you guys but chicks dig mine, i have central heterochromia, a tan ring in green-blue eyes. Not quite sure why, they just like it.

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    3. I have this really weird black line in my green eyes and I always wondered what it was ever since I was little but now I finally found out!

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    4. I feel like I might have central and sectoral--if that's possible? Growing up I had blue/grey eyes and as I got older parts got green and yellow. I have a yellow ring (central) on both green eyes, but a chunk of blue (sectoral) on one of my eyes.

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  4. Probably forced alteration of the human genome. I can remember my parents allowing and forcing me to allow all kinds of slop to be pumped into me. I have got this conditionof the Iris, multi pili gemini, asthma, general constant laziness and discomfort, and when i jog within a mile my jaw starts secreting a metallic taste which begins to ache my entire mouth. So in finale a big UP YOURS intellectual class, UP YOURS industrialists, UP YOURS usurpers and polluters. Once again my incarcerated emotions shall flood out and roll over the world like a wave of fury.

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  5. I have central heterochromia. My eyes are a light blue green and have the golden ring around the pupils. But my eyes also change color.

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    1. Mine change color too. They are central heterochromia with brown outside and green inside. I believe what yours is called is "blue gold". It's really pretty!

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    2. I agree! my are gold around the pupils and mine also change colors!

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  6. Wish i hav a complete heterochromia.. kinda weird though but isn't it kinda cool to hav one? I dont hav any of the other types. my eyes are both dark brown.. it's harmless, right? *sigh*

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  7. I have central heterochromia and always found it quite cool but I didn't know there was a name for it and didn't think it was connected to the same thing as complete heterochromia. learn something new everyday :)

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  8. I have complete heterochromia....one brown eye and one green eye...in my brown eye, its been kinda almost swelling and tearing up...my other eye isnt...im not sure if its just allergies or anything else...

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  9. Fun info. I have complete, pronounced heterochromia - born with one blue and one brown eye. Eventually they muted to what they are today (in my early 50s), one grey and one hazel. Not in my family but, as I like to describe myself in the era of X-Men movies, "I'm a mutant." Uncomfortable to be so different at age 10, but I've grown to love being different. People notice immediately if I'm standing indoors in low light and sun strikes me square in the face. I'd be happy to post a photo (I'm a photgrapher, http://www.JackPhoto.com) here if there were a way to do so...JackATjackphoto.com

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  10. my pig has this its really cool but I cant find any info

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  11. i have complete heterochromia and its really not that cool, its acutally irritating to have evryone want to look in your eyes and one of my eyes work long sited and the other short sited

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  12. I have sectoral/partial heterochromia and I love it. It's only in my left eye, with brown completely covering the top half and the blue covering bottom half. It's completely cut in two horizontally. My right eye is a normal blue color.

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  13. My parents cat has complete hetrochromia; one blue eye, one green. He's 16 now; getting up there.
    I've known two people in my lifetime that had hetrochromia; a girl i went to high school with had one hazel eye and one brown like the first photo, and an old roomate of mine had sectoria hetrochromia in both eyes. One eye was mostly brown with a dot of blue, and his other eye was mostly blue with a few dots of brown.
    I myself have eyes like you; green with a small brown ring around the pupil. My husband also has central hetrochromia but his eyes are blue with a gold ring.

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  14. Great, This specific net webpage is seriously thrilling and enjoyment to learn. I’m an enormous fan from the subjects mentioned. dog nail grinder

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  15. My 5 year old grandson has one blue eye and one green eye. Very striking! Both his parents have blue eyes. I did not know anything about central heterochromia - one of my sons (my grandson's uncle) has central heterochromia - green eyes with a tan ring around the pupil. His wife's eyes are also green with the tan ring! Their son, however, has green eyes without the tan ring.

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  16. My dad has central, brown eyes with a blue ring My mom used to have sectoral heterochromia, brown eyes with little green spots, but her glaucoma medication actually made it almost completely disappear and now her eyes are brown :( Unfortunately though both have it in some way I didn't inherit it, which saddens me.

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  17. Ahhh so that's what it is xD I've got blue eyes with deep amber rings around both

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  18. I have a dog with this it looks amazing! whats the chances ov her pups been the same?

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