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Heterochromia iridis refers to variation in iris color due to differences in melanin content between irides or within different regions of the same iris.

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Classification

1. Complete heterochromia
   • Each eye has a different iris color.
2. Sectoral (partial) heterochromia
   • A segment of one iris differs in color from the remainder.
3. Central heterochromia
   • A distinct inner ring of differing color around the pupil.

Etiology

Congenital

• Isolated benign variant (most common)
• Neural crest cell migration abnormalities
• Waardenburg syndrome
• Congenital Horner syndrome (ipsilateral hypopigmentation)

Acquired

• Fuchs heterochromic iridocyclitis
• Trauma or intraocular surgery
• Chronic uveitis
• Iris tumors (nevus, melanoma)
• Siderosis bulbi
• Prostaglandin analog use (gradual darkening)