Sectoral heterochromia iridum- a good example in a cat

I think this is an excellent, even dramatic, example of sectoral heterochromia iridum in a domestic cat. It is normally referred to as ‘sectoral heterochromia’. Heterochromia is when the eyes are different colours. We sometimes call this “odd-eye” colour. The phrase ‘sectoral heterochromia’ means that the difference in colours occur across one eye, as seen in the photograph. The blue part is due to a lack of melanin and the golden part is because that part of the iris contains melanin which shows up as gold in this instance. The blue part looks blue because the light entering the eye is refracted causing it to appear blue. This is the same reason why the sky looks blue. White light is refracted by particles in the air. Kitten eyes are blue for the same reason: the melanin pigmentation is yet to form.

Sectoral heterochromia in a cat
Sectoral heterochromia in a cat. Photo: Cats of Instagram. The person who posted the photo (a German) was more interested in the cat’s pink nose!
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The reason why sectoral heterochromia normally exists is because of an inherited genetic mutation. It is rare in people but not so rare in cats. It might be acquired through disease, injury, genetic mosaicism or chimerism. I would suggest that the cat in the photograph on this page inherited the condition. It is not harmful to the cat and it looks fantastic.

The cat appears to be a standard, random-bread cat or perhaps a non-extreme British Shorthair. The coat is a bicolour (caused by the piebald gene) which looks like a solid brown-and-white. The face is a totally normal feline face which I like to see. It’s a very good photograph. The pigmentation in the eye is an amazing pure gold. The wriggly little ‘rivulet’ across the blue section of the eye is a capillary blood vessel, I believe.

Straightforward heterochromia or odd-eye colour is really quite common and often seen in cats with a completely white coat. This is because dominant white gene which removes pigmentation from the air strands also removes pigmentation from one eye. Often odd-eyed cats have one yellow and one blue eye. The blue eye is the one without melanin pigmentation in the iris.


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