Heterochromia is a condition that causes a person to have two different eye colors, according to Right Diagnosis. The condition is attributed to a variety of factors, including genetics, injury or inflammation.
Heterochromia is more common in dogs than humans, notes MedlinePlus. Australian sheep dogs and Dalmatians are dogs that can have two opposing eye colors. Other animals, such as cats and horses, can have the condition as well. Humans can get it through various inherited diseases, such as Waardenburg's syndrome and Neurofibromatosis. Glaucoma is another cause of the condition, as are certain medicines that are used to treat the ailment.
Also known as heterochromia iridis, according to Wikipedia, the condition can cause the skin and hair to change color as well. The root cause is excessive or lacking melanin. For heterochromia that is inherited, darker pigmentation can manifest in the form of ocular melanosis. Lighter heterochromia is a trait of piebaldism, which is a condition that is similar to Waardenburg's syndrome.
Acquired heterochromia can take the form of siderosis, which causes dark irises, and it is attributed to iron deposits caused by trauma, adds Wikipedia. Acquired Horner's syndrome is an example of light-colored pigmentation that can be acquired, but it can be inherited as well. There is also central heterochromia, which produces different colors within the center of a single eye.