A sympathetically denervated pupil dilates poorly to cocaine, regardless of the level of the sympathetic interruption because of the absence of endogenous norepinephrine in the synapse. The maximum response is seen 40-60 minutes after instillation of the drops. Postcocaine anisocoria greater than 0.8 mm is sufficient to diagnose Horner syndrome. Hydroxyamphetamine stimulates the release of norepinephrine from presynaptic postganglionic nerve terminals. Note that results of this test will be inaccurate if performed within 24-48 hours of the cocaine test.
Medical care is dependent upon the particular etiology.
Neurologic or neuro-ophthalmic consultation may be considered. Interventional radiologic consultation in cases of suspected carotid artery dissection. Neurosurgical consultation should be considered in cases of suspected aneurysm. Surgical or oncologic consultation is dependent upon the particular etiology. Life-threatening causes of Horner syndrome should first be ruled out with a pertinent history and physical examination.