Horner Syndrome

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  • Lesion of the oculo-sympathetic pathway
  • Causes
    • Central (1st neuron): Brainstem tumor or infarct, spinal tumor, Multiple Sclerosis, cervical spondylosis
    • Preganglionic (2nd neuron): Pancoast tumor, dissection of the internal carotid artery, iatrogenic (neck or thoracic operations); children: Neuroblastoma, Lymphoma
    • Postganglionic (3rd neuron): Dissection of the internal carotid artery, tumor or inflammation of the cavernous sinus, iatrogenic (neck operations), autonomic trigeminal cephalgias (e.g., Cluster headache, paroxysmal hemicrania)


  • Miosis, dilation lag, more pronounced anisocoria in the dark
  • Mild upper lid ptosis, inverse ptosis of the lower lid -> Pseudoenophthalmos
  • Anhidrosis
  • Heterochromia in congenital Horner syndrome



  • Iopidine (apraclonidine) 0.5% or 1%, 1x (evaluation after 30-45 minutes)
    • Reversal of anisocoria in Horner syndrome
    • Contraindicated in children <1-2 years
    • Diagnostic gap: Can be falsely negative in very acute cases!
  • Cocaine Test: Cocaine 10%, 1x (evaluation after 60 minutes)
    • Dilation in a healthy pupil, no effect/no mydriasis in Horner pupil
      • Anisocoria <1 mm: Horner syndrome unlikely
      • Anisocoria >1 mm: Horner syndrome likely
    • mainly in children <2 years (apraclonidine contraindicated!)
    • No diagnostic gap
  • Hydroxyamphetamine 1%, 1x (evaluation after 45 minutes)
    • To differentiate post/pre-ganglionic Horner syndrome
      • Dilation if lesion is in the 1st or 2nd neuron; no dilation with a lesion in the 3rd neuron
  • Phenylephrine 1%, 1x
    • To differentiate post/pre-ganglionic Horner syndrome (alternative to Hydroxyamphetamine test)
    • Dilation with a lesion in the 3rd neuron; no dilation with a lesion in the 1st or 2nd neuron


  • In case of acute Horner syndrome:
    • immediate CT Angiography (head + neck) to rule out a carotid dissection
  • In case of long-standing Horner syndrome:
    • MRI Angiography head + neck (up to T2) within 1(-2) weeks


  • EyeWiki Anisocoria
  • The Wills Eye Manual: Office and Emergency Room Diagnosis and Treatment of Eye Disease; Nika Bagheri MD, Brynn Wajda MD, et al; Lippincott Williams&Wilkins; 7th Edition (2016)
  • Kanski’s Clinical Ophthalmology: A Systematic Approach; Jack J. Kanski MD, Brad Bowling MD; Saunders Ltd.; 8th Edition (2015)