Heterochromia

What is Heterochromia?

Heterochromia means different (hetero-) colors (-chromia). It is a condition in which an individual’s irises are differently colored. (However the term may also be applied to skin and hair, not just irises)

*NOTE

• “Iridis” and “iridium” refer to the iris of the eye. The iris is the thin, circular structure that surrounds the pupil and contains the pigment melanin, which gives our eyes their distinctive color.”

There are 3 different types of Heterochromia: 

• Complete Heterochromia: One iris is a completely different color than the other
• Partial/ Sectoral Heterochromia: A portion of the iris is a different color than the rest of the iris. One or both eyes can have partial Heterochromia 
• Central Heterochromia: The rings or iris area around the pupil has a different color than the outer portions of the iris (like different colored rings!)

• The 2 irises of a person are usually the same color, however, in Heterochromia  , the affected iris may be hypopigmented (hypochromic or lighter) or hyperpigmented (hyperchromic or darker)
  

Heterochromia iridis vs Heterochromia Iridum?
Heterochromia iridis is a specific condition where the iris in one eye possesses a different color than the iris of the other. Heterochromia iridum is a difference in color within the iris of one eye.

When or how does Heterochromia occur?

 Heterochromia can be either Congenital (present at birth) or acquired later in life (through an injury or a disease).

Congenital:  

• Present at birth or when an infant develops Heterochromia after birth
• Majority of the time, kids born with Heterochromia   have no symptoms and their eyes function normally with no specific impairments to vision
• Congenital Heterochromia is usually random or a result of intrauterine disease/ injury. Scenarios in which Heterochromia is inherited (hereditary) are rare yet possible.* 
• Usually the eye color change occurs randomly in individuals with no family history of Heterochromia but can also occur as a result of a genetic mutation, as Heterochromia   is familial in cases of syndromes. 
• Congenital Heterochromia is not rare, as it occurs in 6/1000 births. Congenital Heterochromia is usually unnoticeable as the difference in colors may be very little and is therefore unacknowledged in most situations.
• The majority of the time, congenital Heterochromia is harmless and NOT associated with any systemic abnormality, however there are RARE cases where infant Heterochromia is associated with inherited* congenital syndromes such as:  
• Horner’s syndrome 
• Benign Heterochromia  
• Sturge-Weber syndrome
• Waardenburg syndrome
• Piebaldism
• Hirschsprung disease
• Bloch-Sulzberger syndrome
• von Recklinghausen disease
• Bourneville disease
• Parry-Romberg syndrome

CASE STUDY of PARRY- ROMBERG SYNDROME:

Parry- Romberg Syndrome is a rare disorder in which the soft tissues and skin of half the face (usually the left) deteriorate over time. In relation to Heterochromia, the eyes generally become more sunken and can become hyperchromic or hypochromic. 

Acquired 

• Most cases of Heterochromia Iridis are mild, however, acquired Heterochromia may be due to underlying disease (most commonly due to eye disease). 
• It may also be due to: 
• Eye injury
• Bleeding in the eye
• Swelling, due to iritis or uveitis
• Eye surgery
• Fuchs’ heterochromic cyclitis
• Acquired Horner’s syndrome
• Glaucoma and some medications used to treat it
• Latisse, a repurposed glaucoma medication used cosmetically to thicken eyelashes
• Pigment dispersion syndrome
• Ocular melanosis
• Posner-Schlossman syndrome
• Iris ectropion syndrome
• Benign and malignant tumors of the iris
• Diabetes mellitus
• Central retinal vein occlusion
• Chediak-Higashi syndrome 

Does Heterochromia require treatment?
Heterochromia is typically harmless and therefore does not require treatment. If Heterochromia  is present as a result of a condition, that condition is usually treated, not necessarily the difference in eye color.
 

Does Heterochromia cause any visual impairments?
Typically Heterochromia results in no visual impairments. Heterochromia is usually marked as an unprogressive condition not posing any concern. 

NEVUS in Heterochromia?

What is a Nevus? A Nevus is a birthmark or freckles that may occur on skin as well as IN the eye. A nevus can even occur in the iris! Since Iris Nevi (plural of nevus) are usually brown, they may be easily confused with Heterochromia, if occurring in an iris with a lighter pigment.

• Nevi are benign and do not cause any discomfort. They typically remain the same size.
• Though a Nevi appearing in a hazel, amber, green, or blue iris can be argued to be partial/ sectoral Heterochromia, the term Heterochromia is not used to describe the difference in colors since it is due to a nevus. 

Can Heterochromia occur in animals?

When I think of Heterochromia, I think immediately of playful huskies and fluffy white cats that you see on Instagram.

I was shocked to learn that horses, cows, and buffalo can have Heterochromia as well! Similar to humans, in most cases animals who have Heterochromia have inherited it from a parent (congenital). In fact, the prevalence of Heterochromia in a population can also signify a lack of genetic diversity and the likelihood for a population bottleneck to have happened in the past. But in terms of dogs and cats; Heterochromia is usually found in dog breeds such as…

• Huskies 
• Malamutes 
• Great Danes
• Dalmatians 
• Border collies 
• Shetland Sheepdogs
• Dachshund 
• Chihuahua
• Shih Tzu 
• Catahoula Leopard dogs
• Australian

 Cat breeds which are also likely to have Heterochromia are…

• Turkish Van
• Japanese Bobtail
• Turkish Angora
• Khao Manee
• British Shorthairs
• Cornish
• Munchkins

I was also amazed to learn that Heterochromia is not a native trait to wolves, the cover animal for beautiful multicolored eyes. The classic icy blue and mysterious brown! And that the only way possible for wolves to get the classic ice blue eye is when they have a genetic defect, such as a cataract. 

Heterochromia is an interesting condition which definitely sparked my curiosity. If you’d like to research more, check out these links:

https://www.webmd.com/eye-health/heterochromia-iridis

https://www.aao.org/eye-health/diseases/what-is-heterochromia