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Heterochromia is an ocular condition characterised by different coloured eyes or irises of the same person. Usually, people have the same coloured eyes, but, in heterochromia, people either have one eye as brown and the other as blue or one eye as black and other green or likewise, which are totally differentiable in the person. 
To mention, the iris is the coloured part of the eyes that helps control the amount of light entering the eye. Its colour is determined by the variations of melanin, a natural pigment in our body that also gives skin and hair its natural colour.
Heterochromia is a rare condition of the eyes. In India, the prevalence of different coloured eyes is less compared to other countries. Also, it is common in animals like cats, dogs, rabbits and horses.
In this article, we will discuss details on heterochromia. Take a look.
Types Of Heterochromia
There are three main types of heterochromia. They are:
1. Complete heterochromia: It is also known as heterochromia iridum. In this, one iris is total a different colour from the other.
2. Segmental heterochromia: It is also known as sectoral heterochromia and heterochromia iridis. In this, a larger part of one iris is of a different colour from the other eye. This can develop in one or both eyes and is like an irregular spot on the eye.
3. Central heterochromia: This subtype of heterochromia is characterised by having different colours in the same eyes. For example, people with this condition have an inner ring of the iris of a different colour compared to the colour present along the edges or at the outer ring of the iris.
Causes Of Heterochromia
Eye colour is determined by the concentration of melanin in the irises, however, there are several genetic and physiologic factors that could affect the concentration of this vital pigment and cause variations in the colour of the eyes.
According to a study, a mutation in the gene that helps determine the distribution of melanin in the 8-HTP (hydroxyl tryptophan) pathway can cause the condition. This occurs as a result of chromosomal homogeneity or when a child receives genes from both parents. 
Heterochromia present from birth or develop soon after birth is called congenital heterochromia. It could occur due to many different syndromes such as: 
- Sturge-Weber syndrome
- Waardenburg syndrome
- Parry-Romberg syndrome
- Horner's syndrome 
- Bloch-Sulzberger syndrome
- Bourneville disease.
Heterochromia that occurs at later stages of life is called acquired heterochromia. It could possibly be due to:
- Ocular trauma
- Ocular injury
- Melanocytic infiltration (diffuse iris nevus or melanoma).
- Ocular siderosis or complications due to foreign body.
- Hypo-or hyper-pigmentation of one eye.
- Latanoprost, a glaucoma treatment in which high pressure inside the eyes is treated. 
- Swelling and bleeding in the eyes
- Certain glaucoma medications
- Benign and malignant tumours of the iris. 
- Chediak-Higashi syndrome
- Diabetes mellitus.
Symptoms Of Heterochromia
Some of the symptoms of heterochromia include:
- Difference in colouration between the two eyes. This is the primary symptom of heterochromia.
- Inflammation in the eyes.
- The impression of the sunken eye, in the case of Horner syndrome.
- White colour or unusual while reflection in the pupil or centre of the eyes, especially due to retinoblastoma or eye cancer.
- Other colour differences.
Diagnosis Of Heterochromia
In most cases, heterochromia can be identified just by looking at them, precisely due to visual differences of the eyes.
Heterochromia can become apparent in some lighting conditions or while taking a photo. The condition is mainly diagnosed by ophthalmologists who will determine the eyes and look out for its underlying causes, either genetic or environmental.
If heterochromia is due to a certain disease that is causing symptoms and affecting your quality of life, the ophthalmologist may refer you for a comprehensive eye checkup and to consult an expert on the disease which is causing the condition. If it is genetic, they may suggest genetic or blood tests.
If no health problem is present, which is in majority of the cases, the doctor may just suggest getting a detailed checkup to rule out the chances of any severity.
Treatments For Heterochromia
People with heterochromia often go for its treatment only if the condition is affecting their quality of life. As aforementioned, if there are no symptoms and no underlying cause, it can be a good example of beauty and fashion for people.
Some of the treatment methods of heterochromia include:
- Surgery: If there are cysts present in the iris, surgery could be the best option for it. It also includes laser application. 
- Coloured contact lenses: They could be used for cosmetic reasons when people with heterochromia want to make their eye colours look similar.
- Medications: To treat inflammation, stop bleeding or other forms of injury in the eyes.
Heterochromia is generally a non-threatening medical condition of the eyes and people with the condition often live their lives normally. In newborns with heterochromia, the condition is usually not associated with any underlying anomalies and can be diagnosed and managed early by medical experts, if there are any concerning signs.
However, those who have developed it at a later stage of life, need to consult an expert as early as possible, as it could be due to a certain underlying cause.