Just 11 out of 1000 Americans have two differently colored eyes so the odds aren’t too high but they’re high enough that someone (or some group of people) declared July 12th National Different Colored Eyes Day.
Before you can understand how some people have two different colored eyes, it is important to understand how eyes get their color. Iris color develops during the first few months after birth with the levels of pigment melanin determining how dark eyes will become. The less melanin expressed in the iris, the lighter a person’s eyes look and vice versa. Sometimes the concentration and distribution of melanin isn’t uniform, which leads to a condition known as heterochromia.
There are many different forms of heterochromia. Complete heterochromia is when each eye is distinctly different, such as one blue and one brown. Central heterochromia is when the eyes show various colors, such as a blue iris with a golden-brown ring around the pupil. Sectoral heterochromia is when one iris has a splash of color that’s different from its overall hue.
Although some eye pigmentation abnormalities are inherited from a parent, heterochromia is a common feature of several inherited genetic disorders, such as Waardenburg syndrome and neurofibromatosis. Heterochromia can also be caused by glaucoma.
Please note that a sudden onset of heterochromia could be the sign of an underlying medical condition and a complete eye exam should be conducted by an ophthalmologist to rule out any serious causes.
Source: Live Science