False Negative Apraclonidine Test in a Patient with Horner Syndrome due to Carotid Endarterectomy

Horner syndrome is characterized by miosis and ptosis associated with ipsilateral injury to the sympathetic nervous system. The current gold standard of pharmacologic testing is performed using cocaine, which is costly and difficult to obtain for administration in topical form. More recently, topical apraclonidine has been used and found to result in a reversal of anisocoria in Horner syndrome in most cases.