When we think of cats’ eyes, we generally think of eyes of the same color. However, in both humans (like musical artist David Bowie) and animals – including the mysterious feline and dogs – there are instances where eyes come in two different colors.
In a condition called complete heterochromia, the whole iris of one eye is a different color from the iris of the other eye.
Partial heterochromia, meanwhile, is said to occur when part of one iris is a different color from the rest of the iris in one eye.
The complete form of heterochromia stands out in both beauty and intrigue. One eye will, for instance, be blue while the other will be green, yellow or copper.
This variation in eye color isn't considered a disease. It’s thought to occur in cats that have had illness or injury, and in those that possess the dominant (epistatic) white gene or the white spotting gene – which brings about ‘tuxedo’ and bicolor cats.
The gene stops melanin from reaching and forming pigment in one of the irises. Purebreds like the Turkish Van and Turkish Angora are prone to the genetic mutation.
Some of the cats with two eye colors are deaf but most are not. Sixty to 70 percent of so-called odd-eyed cats can hear, but white cats with one or two blue eyes are more predisposed to genetic deafness.
In some dog shows, such eye color variation can be considered a negative. Conversely, many prize cats are odd-eyed.
In Turkey, the Ankara Zoo and the government help breed pure white Turkish Angoras with one blue eye and one amber eye – and have done since 1917. Legend also has it that the prophet Muhammad's cat, Muezza, was odd-eyed.
Interestingly, a cat may carry the white spotted gene, have no white on its body at all and still manifest the odd-eyed effect.
All kittens are born with blue eyes that change color over the next couple of months of their lives.
In odd-eyed cats, the heterochromia will show as a different shade of blue in one eye and can vary in color until it settles into its adult hue.