Heterochromia Iridis

Most people with heterochromia iridis have no visual impairments.

Heterochromia iridis is a condition in which the iris in one eye has a different color than the iris of the other eye. The iris is the tissue of the eye that surrounds the pupil and imparts a color, whether green, blue, brown, hazel, grey, or other, to the eye.

Heterochromia iridis is differentiated from heterochromia (color difference) iridium (within the iris of one eye).

Iris color is the result of the pigment in the iris. Brown eyes have large amounts of melanin pigment deposits, and blue eyes lack melanin. Although eye color is inherited, the inheritance pattern is complex, interacting with more than one gene. These genes interact to provide the entire constellation of colors. Other genes may determine the pattern and placement of pigment in the iris, thereby accounting for solid brown as opposed to rays of color.

Normally, the two irises of an individual are of the same color. In heterochromia, the affected eye may be hyperpigmented (darker or hyperchromic) or hypopigmented (lighter or hypochromic). Eye color is determined primarily by the concentration and distribution of melanin within the iris tissues.

Heterochromia is classified into three types, which include:

1. Complete heterochromia: This type is characterized by one iris being a completely different color than the other one (i.e. one iris is brown and the other is blue).
2. Partial heterochromia: This type is characterized by a part of one iris being a different color than the rest of it (i.e. a section of one iris is blue while the rest of it is brown).
3. Central heterochromia:  This type is characterized by the center of the iris being a different color than the outer part of it (i.e. the center of the iris is brown while the outer part is green).

Heterochromia can be present at birth (congenital) or acquired. The incidence of congenital heterochromia iridis is approximately six out of 1,000, although, it is hardly noticeable and unassociated with any other abnormality in most cases.

Heterochromia is classified primarily by its time of onset as either genetic (congenital, present at or shortly after birth) or acquired. Most cases of heterochromia are hereditary, and these may be associated with a congenital syndrome. Other cases are acquired and caused by a disease or an injury. Sometimes one eye may change color following certain diseases or injuries. Heterochromia present at or shortly after birth is usually hereditary or due to intrauterine disease or injury. The genetics of eye color determination involves at least eight different genes, with inherited eye color being based on various combinations of gene expression. Congenital heterochromia may be familial and is inherited as an autosomal dominant trait. Environmental or acquired factors can alter these inherited traits. An infant with heterochromia should be examined by both a pediatrician and an ophthalmologist for other possible problems. If another disorder is suspected, diagnostic tests, such as blood tests or chromosome studies, may be done to confirm the diagnosis.

Most cases of heterochromia at birth are genetic and unassociated with any other ocular or systemic abnormality. This is simply called congenital heterochromia iridis. The lighter eye usually shows some loss of iris and therefore is regarded as the affected eye. The lighter iris may be differently colored throughout or only in part.

Congenital syndromes which may be characterized by heterochromia iridis include:

• Waardenburg syndrome is an autosomal dominant genetic condition that can cause hearing loss and changes in the coloring of the hair, skin, and eyes.
• "Piebaldism" is similar to Waardenburg syndrome but is unassociated with deafness. People with this condition have patches of depigmented skin on their head and trunk, as well as on their eyebrows, eyelids, eyelashes, and hair. Affected people sometimes have heterochromia iridis.
• Congenital "Horner's syndrome" is not genetic, but a group of findings due to birth injury or intrauterine brain injury involving the sympathetic nervous system innervation to one eye. On the affected side, the pupil is small, the lid is drooping, and the iris is lighter. It is not associated with hearing loss or additional pigmentation anomalies.
• Sturge-Weber syndrome is a syndrome characterized by a port-wine stain in the distribution of the trigeminal nerve on the face and tumors known as angiomas of the brain and choroid.
• Neurofibromatosis type 1, also known as von Recklinghausen disease, is a disorder in which there are tumors of nerve cells together with disorders of melanin, causing abnormalities of skin (and eye) pigmentation. Lisch nodules are usually present in the iris. These are clear yellow to brown dome-shaped elevations on the iris and, although they are usually present in both eyes, may be more apparent in one eye.
• Tuberous sclerosis, also known as Bourneville disease, causes nonmalignant tumors in various organs including the eyes.
• Hirschsprung disease, a bowel disorder, may be associated with iris heterochromia due to the reduction in iris pigmentation.
• Incontinent pigment, also known as Bloch-Sulzberger syndrome, affects the skin, hair, teeth, nails, and central nervous system. In this condition, the iris may be darker in the affected eye.
• Parry-Romberg syndrome, or progressive hemifacial atrophy, is a condition that causes the breakdown of the skin and soft tissues of half of the face.

Acquired conditions or diseases that may present with heterochromia iridis include:

• The inflammation of iritis or anterior uveitis of any cause, including tuberculosis, sarcoidosis, and herpes simplex, may cause loss of iris pigment in the affected eye.
• Fuchs' heterochromic cyclitis is a condition characterized by low-grade, asymptomatic uveitis in which the iris in the affected eye becomes hypochromic and has a washed-out, somewhat moth-eaten appearance.
• Posner-Schlossman syndrome, or glaucomatocyclitic crisis, may cause a lighter iris with repeated attacks.
• Pigment dispersion syndrome is a condition characterized by loss of pigmentation from the posterior iris surface. This pigment is dispersed throughout the interior of the eye and deposited on various intraocular structures, including the anterior surface of the iris, causing it to darken. This condition also causes pigmentary glaucoma.
• Trauma, either blunt or penetrating, may cause unilateral lightening of the iris through atrophy of the iris.
• Prostaglandin analog eyedrops (Xalatan, Lumigan, Travatan, and others), frequently used for the treatment of glaucoma, may cause darkening of the iris, especially in people with light-colored irises. This occurs from the stimulation of melanin production. This type of medication is also sometimes used for cosmetic purposes (Latisse) to darken and thicken the eyelashes.
• The retained iron-containing intraocular foreign body may cause siderosis (iron deposition within the eye) resulting in a darker iris.
• Blood in the anterior chamber (hyphema) of long duration from trauma can lead to iron deposition in the iris from the breakdown of blood products.
• Ocular melanosis, or nevus of Ota, is a condition characterized by increased pigmentation of the eye and surrounding tissue.
• Iris ectropion syndrome is a condition in which the back of the iris, which is always dark and full of melanin pigment, turns onto the front of the iris through the pupillary space.
• Benign tumors of the iris, iris cysts, and iris abscesses can cause darkening or lightening of the iris.
• Malignant melanoma of the iris or metastatic tumors of the iris.
• Neovascular changes of the iris (rubeosis iridis) resulting from diabetes mellitus or following central retinal vein occlusion.
• Acquired Horner syndrome from neuroblastoma or injury/disease affecting the sympathetic nervous system in the neck.
• Chediak-Higashi syndrome is a rare genetic disorder that may manifest in childhood with recurrent infections, peripheral neuropathy, and color changes in the skin and eye.
• Clouding of the cornea or color changes in the cornea from a multitude of conditions may cause the iris to falsely appear to be different in color. Conditions such as corneal scars, the very common condition of arcus senilis, or the rare condition of Wilson disease can give the appearance of iris color differences.

Familial genetic abnormalities, ocular trauma, and inflammation are all risk factors for the development of heterochromia iridis. The use of prostaglandin analog eyedrops for glaucoma or to stimulate eyelash growth is a modifiable risk factor.

The appearance of different coloration between the two eyes is usually the only symptom or sign. The difference is often so slight that it is only noticed under certain lighting conditions or in close-up photographs. If inflammation or trauma is the cause, other signs or symptoms may be present.

• Heterochromia iridis is termed complete when the entire iris in one eye is different in color than that of the other.
• Segmental heterochromia involves only a radial or piece-of-pie-shaped area of one iris.
• In central heterochromia, an inner ring of the iris is different in color from the rest of the iris.
• The term heterochromia iridium can be used when the heterochromia is incomplete, as in segmental or central heterochromia.

Heterochromia iris is usually noted by the parent of a baby or in acquired cases, by the patient or a family member. Diagnosis can be confirmed through slit lamp examination by an ophthalmologist.

If the heterochromia is secondary to an underlying cause such as inflammation, treatment should be directed at the underlying condition. In situations in which there is a major cosmetic impairment, a tinted contact lens may be used to darken the lighter-appearing eye or lighten the darker-appearing eye. Two differing colored contact lenses may also be used to arrive at an average color.

The vast majority of people with heterochromia iridis have an excellent prognosis and have no visual complaints. Most cases are very mild, nonprogressive, and unassociated with any other illness or eye disease. In patients with associated ocular or systemic problems, treatment of the underlying abnormality is often successful in preventing visual loss.