Here’s a mouthful for your day: Heterochromia Iridum. A genetic mutation causing multiple colors in one iris.
This is of course not to be confused with Heterochromia Iridis: a different color iris in each eye; more common in humans than its’ Iridum counterpart, but still it makes the list of rare diseases affecting less than 200,000 of the US population (look up celebrities like Mila Kunis or Christopher Walken to see their different colored eyes).
When Heterochromia Iridum is seen in humans, it usually signals another disease or problem (like Horner’s Syndrome, Waardenburg Syndrome, infancy nerve damage, chemical exposure, etc.), hence why it is more likely to see it in animals. Certain canine and feline breeds are more genetically predisposed, like my rescue dog Marshall (pictured above). Together his irides look like a Yin-yang: blue on the top of one brown eye and blue on the bottom of the other. I often wonder if it has had an effect on his vision because he doesn’t have great balance and he barks at shadows, but it could be his one-year-old dog brain attached to his awkward 70-pound body.
I’m not really sure what is to blame for his mutation; he’s what I call a “Heinz 52” mix of canine breeds, so I can only guess at his ancestry. Honestly, his eyes are the first thing that drew me to him when I adopted him… surprising, I know.