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What is Heterochromia?
Heterochromia, or ocular heterochromia, is a genetic anomaly that can be hereditary, associated or not with a chronic syndrome, or generated by diseases acquired over the years.
It is characterized by the change in the color of the eyes of mammals, making the color of one eye different from the other. The disease is common in animals, especially dogs and cats, and rare in humans, affecting only an estimated 6 individuals per 1,000 people.
The disorder is caused by a lack or excess of melanin, a pigment responsible for the coloring of the skin, eyes and hair of mammals. In most cases, the unusual coloring of the eyes is almost imperceptible and is not related to any other abnormalities. When inherited from parents, heterochromia has no specific cure or treatment, however it does not promote any symptoms other than the different colors in the eyes.
Types of Heterochromia
There are three predominant pigments in the iris that will determine the final color of the eye: blue, brown and yellow, causing the most common color combinations in the eyes of patients with heterochromia: blue and brown, green and brown and green and blue.
Heterochromia can manifest itself in three ways: sectorial, central and complete. In rare cases, two or more types can mix into a single individual.
Sectoral heterochromia
It happens when the iris has two different colors, with a dominant and the touch of a certain second color. It is common for it to happen in just one eye.
Central heterochromia
Known as a cat’s eye, the iris has two or more circles of color around the outside of the pupil. It happens in only one eye.
Complete heterochromia
Rarer type of the disease, when the two eyes have completely different colors.
Or what causes Heterochromia?
Heterochromia is the result of excess or lack of melanin, the pigment responsible for the color of the skin, hair and eyes. It can be caused by congenital or acquired disorders.
The disease occurs due to a mutation in the EYCL3 gene present on chromosome 15, the DNA sequence responsible for the amount of melanin in the eyes. The colors of the irises develop during the first months after the birth of the child and are determined according to this amount, presenting a dark color when there is a lot of melanin and light when there is little. When the color distribution in the eyes is not uniform, and there is a mixture of two or more shades, heterochromia occurs.
When heterochromia is congenital, the wearer’s eyes are more likely to acquire blue and brown color. If acquired, green and brown coloring is the most common.
Congenital heterochromia
Congenital heterochromia indicates that the patient was born with some genetic alteration that changed the tone of the eyes. In most cases, its cause is hereditary and is not associated with other health problems. However, it can also be a consequence of other diseases, such as:
Síndrome de Waardenburg:
Set of genetic diseases that can cause hearing loss and promote a change in the color of hair, skin and eyes.
Horner Syndrome:
Injury to the sympathetic nerve pathway that affects the nerves of the eyes, face and neck, which may have been caused at birth or in the mother’s uterus. The affected eye has some changes compared to the healthy side, such as the smaller pupil and the lighter iris.
Neurofibromatose:
Rare and serious disease that causes abnormal growth of nervous tissue throughout the body, forming small external tumors. It can cause the affected iris to darken.
Fuchs heterochromia:
Inflammatory disease that, upon reaching the cornea, can pigment or depigment the affected eye.
Chimerism:
Genetic mutation during embryonic development, when two fertilized eggs merge into a single one in the uterus, each containing a different gene for eye color.
Mosaicism:
Variation of one or more chromosomes, genetic code in cells, changing the gene responsible for eye color.
There are, still, other congenital diseases, even more rare, that can cause heterochromia:
- Nevus of Ota;
- Piebaldismo;
- Parry-Romberg syndrome;
- Bloch-Sulzberger syndrome;
- Bourneville’s disease;
- Hirschsprung’s disease;
- Sturge-Weber syndrome.
Acquired heterochromia
There are other causes and diseases that can lead to changes in the melanin of the eyes after birth, they are:
- Iritis;
- Neuroblastoma;
- Traumas;
- Eye bleeding;
- Eye injury or surgery;
- Glaucoma and some drugs used in its treatment;
- Presence of a foreign body in the eyes;
- Benign and malignant melanoma in the iris;
- Mellitus diabetes;
- Síndrome de Chediak-Higashi;
- Occlusion of the central retinal vein;
- Posner-Schlossman syndrome;
- Pigmentary dispersion syndrome.
Heterochromia caused by Medications
Heterochromia can be acquired with the wrong or abusive use of certain drugs indicated for other treatments, as in the case of glaucoma . It is extremely important that the patient never self-medicates and has professional monitoring.
Some drugs that can trigger the disease in its acquired form:
- Latisse;
- Latanoprosta;
- Bimatoprosta;
- Xalatan;
- Lumigan;
- Travatan.
The transmission of familial heterochromia is autosomal dominant, that is, the anomaly is present in the pair of chromosomes that does not determine sex. Therefore, men and women are subject to having the disease, as long as one of the parents is also a carrier.
Symptoms
Heterochromia is manifested by changes in eye color. When you are a carrier from birth, especially if it is your parents’ genetic inheritance, the disease is benign and does not cause any eye disorder or loss of vision, so the only symptom experienced is eye colors that are distinct from each other.
Heterochromia can present itself as the symptom of some other disorder, associated with other effects caused by the disease that originated the problem.
Diagnosis
Right at birth, if the child has different colors in the eyes, the ophthalmologist should be consulted so that he can examine the condition and ensure that the anomaly is not related to other diseases. Adults should follow the same principle, whether the eye begins to change color over the years or abruptly. In the second case, a health problem is likely, so it is important to report adverse symptoms, such as pain, swelling, or redness in the eyes.
The specialist doctor must perform a complete examination of the eye through the slit lamp to rule out possible causes of heterochromia. If you suspect that another disease is responsible, blood tests can be done to confirm the diagnosis.
Is Heterochromia Curable?
When congenital, there is no cure or specific treatment for this anomaly. If it is of interest to the patient, contact lenses can be used to match the eye colors, as long as they are indicated by the ophthalmologist.
Treatment of Heterochromia
Treatment will only be necessary if the heterochromia is the result of some other disease. In this case, the procedures and medications will be indicated according to the causes.
Living and Prognosis
Usually, living with a genetic or rare disease can affect the daily lives of patients and their families. However, heterochromia does not evolve and has no visual complaints.
When associated with any other eye disease, treatments are often successful in preventing visual loss.
Prevention
Because it is a genetic inheritance, heterochromia has no known forms of prevention. However, when it is an acquired defect associated with other illnesses or medication abuse, it can regress, as long as the cause is tackled or prevented through frequent examinations.
Heterochromia is not a serious disease and does not present uncomfortable symptoms to patients. However, care should be taken if there is a sudden change in eye color, as it may be the sign of an underlying medical condition.
Share this article with your family and perform eye exams frequently to ensure your eye health.
