Heterochromia iridum is an innate or acquired ocular condition characterized by an individual having irides — the plural of iris — of contrasting hues. In some people or animals, one iris may be dark brown or blue, while the other iris is green or hazel. This condition, also known as heterochromia iridis, may also express itself through intra-iris color variations, with one eye having two, three or more contrasting sectors of pigment.
Causes include inherited disorders, injuries or cancer and other eye diseases. While some people experience no effects other than the superficial eye color variations, others with this condition can experience a wide spectrum of side effects, including visual distortion, blindness and eye inflammation. Side effects depend on the nature of the cause.
Elderly patients often acquire heterochromia iridum as a result of cataracts or glaucoma. Research findings suggest glaucoma can precipitate changes in ocular pigment for adults in two ways. Glaucoma-linked optic nerve damage and eye pressure can force color abnormalities or prescription eye drops prescribed by doctors to treat glaucoma can contain ingredients that cause hypo-pigmentation or color shifting in the iris.
Clinical research suggests that those suffering from iris cancer can suffer heterochromia iridium. The type of ocular cancer known as melanocytic stromal proliferation can alter the structure of the eye and shift color through the presence of lesions, which can mask parts of the iris. While melanomas of the eye are highly treatable, homogenous color may not return.
Individuals exposed to chemicals or infection can acquire a form of heterochromia iridum caused by Fuchs' Heterochromic Iridocyclitis (FHI), an eye condition during which inflammation of the iris and color loss occur. FHI can be temporary or permanent. Injuries that cause hemorrhaging in the eye can also induce the condition.
Human babies and animals born with heterochromia iridum typically have one of several genetic diseases linked to contrasting eye hues, including Horner’s syndrome and Waardenburg syndrome. In cases of Waardenburg syndrome, a person or animal may not only experience dissimilar eye pigments, but also a variety of skin pigments, a lack of hearing and tooth abnormalities. Horner’s syndrome is a condition in which nerves between the brain and the eye are destroyed or do not develop properly. Newborns who have heterochromia iridum but have no genetic predisposition for any syndromes may have the condition due to nerve damage that occurred from a traumatic injury during childbirth or in the immediate aftermath of birth.