'Heterochromia,' is a Greek word for differences in skin, hair and iris color. 'Heteros,' means different and, 'chroma,' means color. People who experience this usually have one iris that is a different color - darker or lighter than their other iris. The condition is caused by too much or too little pigmentation or melanin. The underlying causes include a number of things:
In anatomy, heterochromia is defined as a difference in coloration, usually of the iris but also of hair or skin. Heterochromia is a result of the relative excess or lack of melanin (a pigment). Heterochromia may be inherited, or caused by genetic mosaicism, chimerism, disease, or injury.
- Eye injury
- Genetic chimerism
Heterochromia is a rare condition, it only affects around 11 people in 1,000 in America. Beside central heterochromia, there are two additional types of the condition. What follows is more in-depth information on heterochromia causes.
Causes of Heterochromia
Heterochromia is classified mainly by its time of onset as either genetic or congenital, present at or shortly after birth, or acquired. The majority of instances of heterochromia are hereditary and these might be associated with a congenital syndrome. Other instances are acquired and caused by an injury or disease. At times, one of a person's eyes might change color after certain injuries or diseases.
Heterochromia present at or shortly after a person's birth is usually hereditary, or due to intrauterine disease or injury. Congenital heterochromia might be familial and is inherited as an autosomal dominant trait. Inherited eye color is determined by a number of genes. Acquired or environmental factors may alter inherited traits. An infant with heterochromia should be examined by an opthalmologist as well as a pediatrician for other potential issues. If another disorder is suspected, diagnostic tests such as chromosome studies or blood tests might be performed to confirm the diagnosis.
Most instances of heterochromia at birth are genetic and not associated with any other form of systemic or ocular abnormality. The condition in this instance is simply referred to as, 'congenital heterochromia iridis.' The person's lighter eye often times shows some loss of iris and is therefore regarded as the eye that is affected. The lighter iris might be differently colored throughout, or only in part. Congenital syndromes which might be characterized by heterochromia iridis include the following.
- Waardenburg Syndrome: Waardenburg syndrome is a genetic condition that may cause hearing loss as well as changes in coloring of the person's skin, hair and eyes.
- 'Piebaldism': Piebaldism is similar to Waardenburg syndrome, although it is not associated with deafness. People with this condition have patches of de-pigmented skin on their trunk and head, as well as on their eyelids, eyebrows, eyelashes and hair. Affected people at times experience heterochromia iridis.
- Horner's Syndrome: Horner's syndrome is not a form of genetic syndrome, but a group of findings due to intrauterine brain injury or birth injury involving the person's sympathetic nervous system innervation to one eye. On the person's affected side their pupil is small, the eyelid is drooping and the person's iris is lighter. Horner's syndrome is not associated with hearing loss or additional pigmentation anomalies.
- Sturge-Weber Syndrome: Sturge-Weber syndrome is characterized by a port-wine stain in the distribution of the trigeminal nerve on the person's face and tumors known as, 'angiomas,' of their choroid and brain.
- Neurofibromatosis Type 1: Also referred to as, 'von Recklinghausen disease,' this is a disorder in which there are tumors of nerve cells together with disorders of melanin, causing abnormalities of the person's eye and skin pigmentation. 'Lisch nodules,' are often present in the person's iris. Lisch nodes are clear yellow to brown dome-shaped elevations on the person's iris and while they are usually present in both of a person's eyes they might be more apparent in one eye.
- Tuberous Sclerosis: Tuberous sclerosis is also referred to as, 'Bourneville disease,' and causes nonmalignant tumors in different organs, to include an affected person's eyes.
- Hirschsprung Disease: Hirschsprung disease is a bowel disorder that might be associated with iris heterochromia due to reduction in the person's iris pigmentation.
- Incontinentia Pigmenti: Incontinentia pigmenti is also known as, 'Bloch-Sulzberger syndrome,' and affects a person's hair, teeth, nails and central nervous system. The person's iris might be darker in the eye that is affected.
- Parry-Romberg Syndrome: Parry-Romberg syndrome is also referred to as, 'hemifacial atrophy,' and is a condition that causes the breakdown of a person's skin and the soft tissues of half of their face.
Acquired Diseases or Conditions and Heterochromia Iridis
Some acquired conditions or diseases might be present in people with heterochromia iridis. These conditions or diseases include the following:
- Malignant Melanoma: Malignant melanoma of the affected person's iris or metastatic tumors of their iris.
- Trauma: Trauma, either penetrating or blunt, might cause unilateral lightening of the iris through atrophy of the iris.
- Neovascular Changes: Neovascular changes of a person's iris resulting from diabetes, or after central retinal vein occlusion.
- Ocular Melanosis: Ocular melanosis is a condition characterized by increased pigmentation of a person's eye and surrounding tissues.
- Benign Tumors: Benign tumors of a person's iris or iris cysts, as well as iris abscesses, may cause lightening or darkening of the person's iris.
- Retained Iron-Containing Intraocular Foreign Body: The condition might cause, 'siderosis,' or iron deposition within the person's eye, resulting in a darker iris.
- Posner-Schlossman Syndrome: Posner-Schlossman syndrome is also referred to as, 'glaucomatocyclitic crisis,' and might cause a lighter iris with repeated attacks.
- Acquired Horner Syndrome: Acquired Horner syndrome from neuroblastoma, disease or injury which affects a person's sympathetic nervous system in their neck.
- Blood in the Anterior Chamber: Blood in the anterior chamber of long duration from trauma may lead to iron deposition in the person's iris from the breakdown of blood products.
- Iris Ectropion Syndrome: Iris ectropion syndrome is a condition in which the back of the person's iris, which is always dark and full of melanin pigment, turns onto the front of their iris through the pupillary space.
- Inflammation of Iritis or Anterior Uveitis: Inflammation associated with this condition from any cause to include sarcoidosis, tuberculosis, or herpes simplex might cause a loss of iris pigmentation in the person's affected eye.
- Chediak-Higashi Syndrome: Chediak-Higashi syndrome is a rare genetic disorder that may manifest in a person's childhood with peripheral neuropathy, recurrent infections, as well as color changes in an affected person's eye and skin.
- Fuchs' Heterochromic Cyclitis: Fuchs' heterochromic cyclitis is a condition characterized by a low-grade, asymptomatic uveitis in which the person's iris in their affected eye becomes hypochromic and has a washed-out, somewhat moth-eaten appearance.
- Pigment Dispersion Syndrome: Pigment dispersion syndrome is a condition characterized by a loss of pigmentation from the posterior iris surface. The pigment is dispersed throughout the interior of the person's eye and deposited on various intraocular structures, to include the anterior surface of the person's iris causing it to darken. The condition also causes pigmentary glaucoma.
- Prostaglandin Analogue Eyedrops: Prostaglandin analogue eyedrops such as Lumigan, Xalatan, and Travatan, often used for the treatment of glaucoma, might cause darkening of a person's iris; particularly in people who have light-colored irises. The condition happens from the stimulation of melanin production. The medications are at times used for cosmetic reasons in order to darken and thicken a person's eyelashes.
Clouding of a person's cornea or changes in color in their cornea from a number of conditions might cause their iris to falsely appear to be a different color. Conditions such as corneal scars, the common condition of, 'arcus senilis,' or the rare condition of Wilson disease might give the appearance of iris color differences.
Types of Heterochromia
Heterochromia manifests itself in one of three forms; sectoral, central and complete. It is also examined by how the onset occurred, genetic or acquired. While the majority of instances of this condition are genetic, there are also some instances where an eye changes color due to an underlying condition, or an eye injury. What follows are descriptions of the types of heterochromia.
- Sectoral Heterochromia: In sectoral heterochromia, the person's iris has two entirely different colors in the same area. Sectoral heterochromia appears as an irregular spot that is a different color than the person's eye color and does not form a complete ring around the person's pupil.
- Central Heterochromia: Often times referred to as, 'cat eyes,' this form is manifested by the appearance of two different colors in one of a person's irises. One color is in the central portion of the person's iris, while the outer edge is a different color. The true color of the person's eye is always the outside color of their affected iris.
- Complete Heterochromia: Complete heterochromia happens when the person's eyes are two different colors. Complete heterochromia is the most dramatic of all the forms of heterochromia. A person might have one green eye and one blue eye, or a brown eye and a blue eye. Complete heterochromia is also common in animals, such as cats.
A health care provider might ask questions to help evaluate the cause such as, 'Did you notice the two different eye colors when the person was born, shortly after their birth, or recently? The health care provider may also ask if the person is experiencing any other symptoms. An infant with heterochromia should be examined by both an opthalmologist and a pediatrician for other potential issues.
A complete eye exam may rule out the majority of causes of heterochromia. If there does not appear to be an underlying disorder, no additional tests may be needed. If another disorder is suspected, diagnostic testing such as chromosome studies or blood testing might be performed in order to confirm the diagnosis.