They say that the eyes are the windows to the soul. When you first meet someone eye contact is important. Whether you are consciously aware of it or not, any time you are talking to someone, you are visually noticing their eyes as part of their general facial expression, as well as other forms of non-verbal communication.

One of the most striking things about human eyes is the chance for each of a person’s eyes to be different colors. In some cases, the difference might be so subtle as to barely be noticed. In other cases, this condition called Heterochromia can reveal striking contrast between the person’s left and right eyes. David Bowie, the world famous musician is widely known for having heterochromia.

How Common Is Heterochromia?

Statistically heterochromia occurs in roughly .006% of human beings, which works out to being roughly one out of every six individuals. It’s also worth noting that heterochromia is not limited to just homo sapiens.

Our pets can also develop heterochromia in conjunction with other genetic abnormalities. In felines for example, a cat with one blue eye and one green eye also tends to be deaf in the ear on the blue-eyed side. In certain dog breeds like the Siberian husky heterochromia is a somewhat common genetic trait with no appreciable side effects on the dog itself.

Though in humans heterochromia can occur for a variety of reasons. There are even different types of heterochromia that don’t necessarily show up as dramatic contrast between the irises of each eye.

What Are The Different Types Of Heterochromia?

There are a few different types of heterochromia. While some of the extreme versions cause a dramatic difference between one iris and the next, there are more subtle types of heterochromia that might not always be noticeable to the casual observer.

Central Heterochromia

This is the more common type of Heterochromia. It tends to cause a modest difference in the color of the iris close to the pupil of the eye. It can affect one or both eyes.

Complete Heterochromia

This is a more rare, and dramatic version of heterochromia that causes a dramatic difference in color between the iris of the left and the right eye.

Sectoral or Segmental Heterochromia

This is another type of heterochromia that is more subtle. It tends to affect only a small patch of one iris on one eye. Most people with segmented heterochromia only have it affecting one eye. Though it is possible for there to be a segmented color change in both eyes.

What Causes Heterochromia?

Most of the time the different colors in the iris seen in heterochromia cases is little more than a benign genetic trail that affects the way the iris develops early on in life. Though it is possible for some diseases and injuries to cause heterochromia.

What Diseases & Medical Conditions Cause Heterochromia?

It is possible for certain medical conditions and diseases to cause the iris of one or both eyes to change in color. Some are the after effects of an injury or an acute medical condition that went untreated. The following are some of the non-genetic causes of heterochromia.

Horner’s syndrome

This condition results from a lesion on the sympathetic pathways that supply the head and neck region.

Fuchs’ Heterochromic Iridocyclitis

This is typically the result of chronic low grade unilateral, ocular inflammation that alters the eye in a variety of ways, including gradual alterations in the pigment of the iris.

Glaucoma Complications

Some cases of glaucoma can cause an increase in pressure in the eye, which can affect the pigment of the iris.

Pigment Dispersion Syndrome

This occurs when the pigment rubs off the back of the iris, and then floats around to other parts of the eye. PDS can also cause eye pressure problems and related complications.

Ocular Melanosis

It is caused by an increase in the number of melanocytes in the iris, and choroid of the eye as well as other important surrounding structures. The gradual overproduction of pigment by these cells can even start to block the trabecular meshwork that allows fluid to efficiently drain from the eye.

Posner-Schlossman Syndrome

Also known as glaucomatocyclitic crisis, which is an acute disease involving unilateral, recurrent attacks of elevated intraocular pressure. It is often accompanied by mild anterior chamber inflammation, which can further alter the appearance of the eyes.

Diabetes

This increasingly common blood sugar handling disease can have a profound effect on several aspects of eye health. This includes complications related to inflammation that pressure in the eye which can affect the health and general color of the iris.

Central Retinal Vein Occlusion

This is a condition of the eyes that affects the arteries and blood vessels that supply oxygen and key nutrients. When the blood supply to the retina and other important structures is impeded it can affect the surrounding cells including the pigmented cells of the iris.

Iritis

Also known as uveitis, this condition causes increased swelling and irritation with inflammation in the colored ring near the pupil of the eye. It generally affects the middle layers of the iris, and can potentially affect the health of the retina.

Can Heterochromia Cause Blindness?

The change in the color of the iris itself can’t directly cause blindness. Indeed, people with genetic heterochromia do not experience any direct impact of their visual acuity. It’s when heterochromia is a resulting symptom of an injury or another more serious eye health condition that blindness can occur. Your eye doctor can diagnose and help you understand your treatment options.

Can Color Contacts Be Used To Hide Heterochromia?

There are some people with heterochromia who are uncomfortable with the disparity in color between their two eyes. In a case like this, your eye doctor might prescribe color contacts. This might be a single color contact to correct the altered eye to match the other, or a pair of color contacts to alter the overt appearance of both eyes to whatever shade you prefer.

What Should I Do If I Notice A Change In My Eye Color?

Acquired heterochromia, which is the result of something other than genetics, is often related to some type of eye injury or underlying eye health condition. If you have noticed a gradual, or pronounced change in the color of one or both of your eyes, you should schedule an appointment with your eye doctor as soon as possible. They can accurately diagnose the underlying cause and help you understand your treatment options.