– Ed

Heterochromia can occur in animals

The iris is basically the area around our pupils that gives colour to our eyes. It is the amount of melanin that determines what colour our eyes will be. Blue eyes have less melanin than brown eyes. Heterochromia means different coloured eyes, as in one blue and one brown eye. Hetero means different and chromia means colour. Heterochromia, is not an eye disease and it does not affect our vision or pose any thread to ocular health.

How rare is Heterochromia Iridis?

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

Heterochromia is classified primarily by the time of onset as either genetic (congenital, presents 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.

Congenital heterochromia may be familial and is inherited as an autosomal dominant trait. Inherited eye colour is determined by multiple genes. Environmental or acquired factors can alter these inherited traits.

An infant with heterochromia should be examined by both a paediatrician 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.

Types of heterochromia

Complete heterochromia: The iris of one eye is a completely different colour than the iris of the other eye.
Partial heterochromia: Only a sector of the iris of one eye has a different colour than the rest of the iris of that eye. Partial heterochromia can occur in one eye or both eyes.
Central heterochromia: The iris has a different colour near the border of the pupil (compared with the colour of the rest of the iris), with spikes of the central colour radiating from the pupil toward the middle of the iris.

Iris Nevus

Iris Nevus

Something that’s often confused with heterochromia is a benign growth called an iris nevus. A pigmented nevus in the iris usually is round in shape and brown in colour. Usually, only one iris nevus is present, but it’s possible to have more. It might be argued that a brown iris nevus on a blue, green or hazel eye is a type of partial heterochromia. However, the term heterochromia usually isn’t used when the cause of the colour variation in the iris is due to a nevus.

Iris nevi (plural of nevus) typically remain stable in size. If you have an iris nevus, your eye doctor usually will want to see you every six months (for a while, at least) to measure its size and rule out any growth that could indicate malignancy. Very few iris nevi turn into melanomas (cancerous).

Many famous people have heterochromia

Kate Bosworth

Demi Moore, Christopher Walken, Dan Aykroyd and Jane Seymour, to mention a few, have heterochromia. Having heterochromia is not necessarily a disaster, because it can present quite an exotic look.

The David Bowie Story

David Bowie, the late singer, songwriter, actor and record producer, was born with blue eyes. When he was a teenager, he got into a fistfight with a school buddy, over a girl they both fancied. Bowie received a blow to his left eye, and the injury left his pupil permanently dilated. The severe anisocoria from the damage made him look as though he had two different coloured eyes, a blue right eye and a nearly black left eye.

David Bowie’s eyes: Anisocoria, not Heterochromia (Image: Everett Collection / Shutterstock.com)

Despite the fact that he carried the result of the fight all his life, Bowie remained lifelong friends with the culprit, George Underwood, who also became his artistic collaborator.

Be safe, have an eye exam

Though most cases of heterochromia are congenital and benign, if you or your child has different coloured eyes (or different coloured segments of one or both eyes), go for a comprehensive eye examination with your Eye Care Professional to rule out any other causes.

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