Eye pigmentation is determined by melanocytes.
Thus, one way to develop heterochromia is to have an injury to this portion of the nervous system. Congenital cases are generally inherited as autosomal dominant traits. Horner syndrome is the result of damage or paralysis of the sympathetic nerves in one side of the face. At least one case of Horner syndrome acquired from an accident as a teenager. The severity varies widely and some affected persons escape deafness.