Different eye color is a disease or a gift?
Heterochromia is when a person’s irises are different colors. There are a few kinds of heterochromia. Complete heterochromia is when one iris is a different color than the other. When part of one iris is a different color than the rest of it, this is called partial heterochromia. Central heterochromia is when there is an inner ring that is a different color than the outer area of the iris.
But what causes heterochromia and should people with the condition be concerned?
What causes heterochromia?
The most common cause of heterochromia is a genetic mutation that results in an individual born with two differently colored eyes. This mutation is not usually harmful and, as mentioned, usually does not influence the quality of vision. Some versions of congenital heterochromia can be linked to rare diseases such as Waardenburg syndrome, though these are less common. This genetic tweak changes the way the body expresses pigmentation in the iris, leading to the differing colors. There are other ways to acquire heterochromia after birth, however, that are not related to the usual benign mutation.
Severe eye trauma is perhaps the most common cause, as was the case with the famous musician David Bowie. Trauma that causes damage to the iris may result in color changes both temporary and permanent as well as affect visual acuity. Some eye diseases, such as glaucoma — and even one of the primary medications used for glaucoma treatment — can lead to heterochromia-like aberrations in eye color. Medical conditions such as diabetes, as well as eye surgery, can sometimes trigger these changes as well, but acquired heterochromia of this type is substantially rarer than the congenital types.
Types Of Heterochromia
There are three types of heterochromia, based on where the different colors are located:
1. Complete heterochromia. This is where the iris of one eye is a completely different color than the iris of the other eye.
2. Partial heterochromia (or sectoral heterochromia). This is where only a portion (or sector) of the iris of one eye has a different color than the rest of the iris of that eye. Partial heterochromia can occur in one eye or both eyes.
3. Central heterochromia. In this type of heterochromia, the iris has a different color near the border of the pupil (compared with the color of the rest of the iris), with spikes of the central color radiating from the pupil toward the middle of the iris.
How Rare Is Heterochromia in Humans?
Not much research has been done to come up with a good estimate of the prevalence and incidence of heterochromia.
In one study published in 1966, 7000 Maryland school children were examined for the incidence of heterochromia. About 0.7% of the children examined had segmental heterochromia. No incident of complete heterochromia was reported.
Another study performed in 1979 with a larger sample of over 25000 people from Vienna reported different types of heterochromia. In this study, about 0.3% of the people examined had the condition. It was also found that females were two times more likely to have heterochromia than males.
The result of such studies should be interpreted with care because the sample was restricted only to specific geographical locations. Hence the results maybe different in other geographical locations or when we consider the world as a whole.
Heterochromia in Dogs and Cats
Heterochromia is believed to be more common in animals than in humans.
Some breeds of domestic cats such as the Angora cats are well known for their high incidence of complete heterochromia. They are called Turkish Angora Cats because it is believed that they originated from central Turkey.
Huskies are famous for their good looks. Maybe it’s their striking masks and piercing eyes that makes them so appealing. Every now and then you’ll find one with two different colored eyes. Huskies are among dog breeds that are more susceptible to express heterochromia.
That being said, you shouldn't take eye color alone as your major consideration should you decide to get a pet. There are definitely other wonderful traits you should also consider.
Heterochromia diagnosis and treatment
If your infant has heterochromia, he or she should be examined by an ophthalmologist. The ophthalmologist will confirm the appearance of heterochromia and look for any underlying causes. In most cases, there will be no concerning disease or condition causing the eye color variation. However, it is important to rule out these conditions.
If you get heterochromia as an adult or it changes in appearance, see your ophthalmologist. He or she can perform a detailed eye exam to rule out any underlying causes and come up with a treatment plan if necessary.