What Is Heterochromia?

The word "heterochromia" derives from the Greek words heteros (different) and chroma (color). As the name suggests, people with heterochromia, also called heterochromia iridis, have a different color in the iris (the area around the pupil) of each eye. There are also different types of heterochromia: complete, partial, and central heterochromia. Some people are born with it, while others may develop heterochromia later in life due to an injury, medication, or illness.

While it is determined by genetics, iris color is not constant. Eye color is directly related to the amount and quality of melanin in the iris. People with brown eyes have a large amount of melanin in the iris, while people with blue eyes have much less of this pigment. Various diseases can affect how the melanin is distributed over the iris.

Types of Heterochromia

There are a few types of heterochromia, and they are defined by the location where the color is different.

Central Heterochromia

Central heterochromia is when there is an inner ring that is a different color than the outer area of the iris. It often happens in both eyes, with two separate colors appearing in each eye. People with this type of heterochromia will have a shade of gold or brown near the border of the pupils. A common form of central heterochromia shows up as predominantly blue eyes with a smaller ring of brown in the center radiating outward.

Complete Heterochromia

Complete heterochromia is when one iris is a different color than the other. For example, one of them is green, while the other one is brown.

Partial Heterochromia

Partial heterochromia is when part of one iris is a different color than the rest of it. The pattern of colors in this form of heterochromia is often unique and varied. People can develop it in one or both eyes.

Heterochromia Symptoms

In most cases, children born with heterochromia will experience no other symptoms because they do not have any other problems with their eyes or general health. However, in some cases heterochromia can be a symptom of another condition.

Causes

An infant can be born with heterochromia or develop it soon after birth. In these cases, it is called congenital heterochromia. When people develop heterochromia later in life, this is called acquired heterochromia. The causes are different for congenital and acquired heterochromia.

Congenital Heterochromia

Causes of heterochromia in infants include:

• Horner syndrome: When this condition happens in children who are less than 2 years old, it can cause complete heterochromia. Horner syndrome affects the cervical sympathetic nerves, which can interfere with melanin pigmentation (coloring) in the iris. 
• Sturge-Weber syndrome: It is a rare disorder characterized by a port-wine birthmark, and it can cause several eye abnormalities. Some children with Sturge-Weber syndrome develop complete heterochromia due to hyperpigmentation in the affected area.
• Waardenburg syndrome: It is a group of genetic conditions that can cause hearing loss and changes in the coloring of hair, skin, and eyes. In this case, patients can develop any type of heterochromia.
• Hirschsprung disease: This is a bowel disorder often associated with partial heterochromia. 
• Bloch-Sulzberger syndrome: This condition affects the central nervous system, hair, teeth, skin, nails, and eyes. When it reaches the visual system, the affected eye becomes darker. 
• Piebaldism: This condition is characterized by a lack of pigment in the skin, eyes, and hair. As a result, some parts of those areas have a lighter color. 
• Bourneville syndrome: Also known as tuberous sclerosis, it is a rare syndrome that causes noncancerous tumors in different parts of the body. When these tumors press on nerves in certain areas, they can affect melanin pigmentation and iris color.

Acquired Heterochromia

Causes of acquired heterochromia include:

• Neuroblastoma: This is a cancer that develops from immature nerve cells found in several areas of the body and primarily affects children. It is the most common extracranial solid tumor in children. It can be associated with Horner's syndrome, which will trigger heterochromia.
• Fuchs' syndrome: It is also known as heterochromic cyclitis syndrome and is a form of uveitis (inflammation of the middle layer of the eye). In this case, heterochromia is predominantly seen in patients with a lighter-colored iris.
• Pigment dispersion syndrome: Pigment dispersion syndrome occurs when pigment granules (small particles) that normally adhere to the back of the iris flake off into the clear fluid produced in the eye. The pigmentation increase can lead to changes in eye color.
• Central retinal vein occlusion: It is a common retinal vascular disease, especially among older people. It can affect the eye system in different ways, including changing the color of the eye.
• Eye melanoma: It is a type of cancer that develops in the cells that produce pigment. It often develops among the three layers in the eye and goes unnoticed. People with this type of cancer may have a dark spot on the iris.
• Eye injuries or traumas: Eye injuries and traumas can lead to eye depigmentation.
• Glaucoma medication: Some medications can change eye color. Patients who use latanoprost, which is used to treat glaucoma, often develop heterochromia after some years of using the medication. 

Diagnosis

An ophthalmologist can diagnose heterochromia. They 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, your ophthalmologist can perform a detailed eye exam to rule out any underlying causes and come up with a treatment plan if necessary.

Treatment

Heterochromia is often benign and doesn't require any treatment since it won't cause any harm. If there are underlying diseases or injuries, the treatment will depend on each case and the patient should discuss the options with the doctor. 

A Word From Verywell

People should check with a doctor if their eye color changes are sudden, especially after eye trauma and other symptoms. Only a doctor can tell if the change in the heterochromia is associated with a disease. However, there is no reason to worry about heterochromia in most cases and it tends to be benign. This condition is generally not harmful, and it does not affect a person's quality of life.