Heterochromia

Heterochromia is a condition where one iris is a different colour from the other (complete heterochromia), or where a part of one iris is a different colour (sectoral or partial heterochromia).

Types of Heterochromia (Expanded)

Complete heterochromia: Each eye is a different colour (e.g., one blue, one brown).
Sectoral (partial) heterochromia: A segment of the iris is a different colour from the rest.
Central heterochromia: A ring or spikes of a different colour radiate from the pupil.

Causes (Expanded)

Heterochromia can be:

Genetic: Mosaicism, chimerism, X-inactivation (especially in females), or inherited as part of syndromes (e.g., Waardenburg syndrome, Sturge–Weber syndrome, Hirschsprung's disease, piebaldism).
Acquired: Injury, disease (e.g., Fuchs heterochromic iridocyclitis, pigment dispersion syndrome, neoplasms), certain medications (e.g., prostaglandin analogues for glaucoma), or viral infection in utero.

Associated Syndromes and Disorders

Waardenburg syndrome: Heterochromia, deafness, pigmentary anomalies.
Sturge–Weber syndrome: Port-wine stain, neurological symptoms, possible heterochromia.
Pigment dispersion syndrome: Loss of iris pigment, can cause heterochromia and glaucoma.
Horner's syndrome: Can cause lighter iris in affected eye.

Heterochromia in Animals

Heterochromia is common in some animal breeds (e.g., Siberian Huskies, Turkish Van cats, horses) and is often due to selective breeding or genetic factors. In animals, it is usually benign.

Cultural and Historical Notes

Heterochromia has been noted since antiquity (e.g., Aristotle, Byzantine emperor Anastasius I). It is sometimes associated with mystique, uniqueness, or supernatural qualities in literature and folklore.

Writing Tips (Expanded)

Use heterochromia to create memorable, visually distinctive characters.
Can symbolise uniqueness, mystery, or a hidden past.
Consider using heterochromia as a subtle indicator of underlying health or genetic conditions.

Causes

Genetic mosaicism, chimerism, or inheritance
Injury, disease, or certain medications
X-inactivation (especially in females)

Types

Complete heterochromia: Each eye is a different colour (e.g., one blue, one brown).
Sectoral (partial) heterochromia: A segment of the iris is a different colour from the rest.

Writing Tips

Use heterochromia to create memorable, visually distinctive characters.
Can symbolise uniqueness, mystery, or a hidden past.