Heterochromia: The science behind two different coloured eyes

When a person has different shaded eyes such as one blue and the other green, it refers to heterochromia where “hetero” is for different and “chromia” represent colours respectively. Other medical terminologies for different shaded eyes are heterochromia iridis or heterochromia iridum. Here, iridis and iridum are associated to the iris of the eye which is a thin, spherical structure around the pupil, containing melanin; a natural pigment which give our eyes their distinct shades.

The amount or volume of melanin in the iris determines the shade we’re likely to have such as blue, green, hazel or brown. That being said, blue eyes are due to least amount of melanin whereas brown have the most. It must be noted that heterochromia in most cases is benign; means it isn’t any eye disease and doesn’t affect vision. In fact, heterochromia adds charm and exoticness to a personality. A number of famous Hollywood celebrities have heterochromia.

Categories of heterochromia
Based on location of the various shades, there’re three different types of heterochromia;
  • Complete
In complete heterochromia, iris of the eye is of entirely different shade than that of the other eye.
  • Partial/Sectorial
When a specific portion or sector of iris is of a different colour than the rest, partial heterochromia occurs and it may be present in both the eyes.
  • Central
When iris is of a different shade from the edge or border of the pupil as compared to the rest, this is referred to as central heterochromia. Spikes of central shade radiates from the pupil all the way towards iris’s middle.

Heterochromia is often confused with a benign growth known as an iris nevus which is a pigmented nevus of circular shape and brown shaded. In most cases, only a single iris nevus is present but there’s always a possibility for more.

The Iris nevi (plural of nevus) remains constant in size however, your eye specialist in Dubai would surely recommend having it checked every six months just to measure its size and prevent malignant growth that can be harmful.

Heterochromia is mostly nonthreatening or benign which means an infant can be born having it or may become apparent at later stages of child development when the iris attains complete amount of melanin also referred to as congenital heterochromia.

This is genetically inherited whereas benign heterochromia can also occur due to genetic mutation at the time of development of embryo. Acquired heterochromia is that which develops at later stage in life with certain eye injuries, glaucoma medication intake and uveitis becoming the core causes.

A repurposed glaucoma medication known as Latisse is now commonly used as a cosmetic agent to condense the eyelashes and may alter shade of the iris as well.

A word on Anisocoria
Anisocoria is another condition which makes people look as if theirs are two different shades of the eyes and commonly characterised by unequal sizes of pupil. Can be present at birth and perfectly harmless, size difference between both the eyes is mostly less than a millimetre. In rare cases, difference in pupil size can be significantly large especially if you’ve received a traumatic eye injury or nerve palsy.

It’s always better to have a detailed insight on both threatening and nonthreatening heterochromia by an eye specialist in Dubai for assurance.

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