Background: Heterochromia iridis, asymmetry of iris pigmentation, has been well described with congenital Horner syndrome. Acquired heterochromia associated with lesions in the ocular sympathetic pathways in adulthood, however, is rare. Methods: Two cases are reported in which sympathectomy in adults resulted in ipsilateral Horner syndrome with heterochromia. In each case, pharmacologic testing with cocaine and hydroxyamphetamine was performed. Results: In both cases, sympathectomy occurred at the level of the second order neuron, but hydroxyamphetamine testing suggested at least partial third order neuron involvement. Conclusion: Acquired heterochromia can occur in adults. The partial response to hydroxyamphetamine in the two cases presented may reflect trans-synaptic degeneration of the postganglionic neuron. A reduction in trophic influences on iris melanocytes may have contributed to the observed heterochromia.
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