Andrew A. Dahl, MD, is a board-certified ophthalmologist. Dr. Dahl's educational background includes a BA with Honors and Distinction from Wesleyan University, Middletown, CT, and an MD from Cornell University, where he was selected for Alpha Omega Alpha, the national medical honor society. He had an internal medical internship at the New York Hospital/Cornell Medical Center.
Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.
Heterochromia can be present at birth (congenital) or acquired. The incidence of congenital heterochromia iridis is approximately six out of a 1,000, although in most of these cases, it is hardly noticeable and unassociated with any other abnormality.
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 due to 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. Congenital heterochromia may be familial and is inherited as an autosomal dominant trait. Inherited eye color is determined by multiple genes. 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, a genetic condition that can cause hearing loss and changes in 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 a genetic syndrome, 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, 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 reduction is iris pigmentation.
Incontinentia pigmenti, 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:
Fuchs' heterochromic cyclitis is a condition characterized by a 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 analogue 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.
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.
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.