Horner’s Syndrome

We have heard Horner’s syndrome like a thousand times during our med school years, but today I came across something interesting. I was amazed when I got to know that we could localize the site of the lesion just by analyzing anhidrosis. Okay then, let’s get into more details.

Horner’s syndrome is characterized by miosis, partial ptosis, anhidrosis  & enophthalmos due to damage to the sympathetic nerve supply of the eye, head and neck.

To obtain a proper understanding of the pathophysiology, it is important for us to learn the anatomy behind this.

Sympathetic Innervation Of The Eye

Sympathetic Innervation Of The Eye

Sympathetic innervation of the eye consist of….

  • First order neuron
    • Posterior hypothalamus to intermediolateral cell column of the spinal cord at the level of C8 – T2
  • Second order neuron
    • Preganglionic pupillomotor fibers exit the spinal cord and enter the cervical sympathetic chain and later synapse in the superior cervical ganglion
    • Postganglionic pupillomotor fibers exit the superior cervical ganglion and ascend upwards giving off vasomotor and sudomotor branches
  • Third order neuron
    • Postganglionic pupillomotor fibers enter the cavernous sinus along with the internal carotid artery
    • Enter the orbit though superior orbital fissure
    • Long ciliary nerves innervates the iris dilator and the Müller muscle


  • Congenital – Heterochromia iridium
    • Present before 2 years of age
    • There is a colour difference of the iris in the affected eye due to relative hypopigmentation of the iris
  • Acquired
    • Damage to first order neuron / Central lesions
      • Cerebral vascular accident (lateral medullary syndrome)
      • Syringomyelia
      • Multiple sclerosis
      • Brain tumors
      • Encephalitis
      • High cervical cord lesion (Spinal cord injury)
    • Damage to second order neuron / Pre-ganglionic lesions
      • Trauma – Injury to lower brachial plexus
      • Pancoast tumor
      • Cervical rib
      • Iatrogenic
        • Neck surgery – Thyroidectomy
        • Insertion of central line
    • Damage to third order neuron / Post-ganglionic lesions
      • Internal carotid artery dissection
      • Carotid aneurysm
      • Cavernous sinus thrombosis
      • Cluster headache
      • Migraine headache

Clinical Presentation & Lesion Localization

There are some features of Horner’s syndrome that present irrespective to the site of lesion. They are….

  • Partial ptosis
    • Due to denervation of Müller muscle which helps in eye opening
    • Ptosis is < 2 mm
  • Upside down ptosis
    • Due to denervation of the lower eye lid muscles
    • There is slight elevation of the lower eye lid
  • Miosis
    • Due to denervation of iris dilator muscles
  • Enophthalmos (Sunken eyes)
    • Not clearly seen in most patients

Anhidrosis has various presentations depending on the site of lesion.

  • Damage to first order neuron / Central lesion
    • Anhidrosis on the ipsilateral face, arm and trunk
  • Damage to second order neuron / Pre-ganglionic lesion
    • Anhidrosis of the ipsilateral face
  • Damage to third order neuron / Post-ganglionic lesions
    • Anhidrosis is absent / present above the ipsilateral brow

Other clinical features will depend on the underlying pathology.


Investigations should be directed to find out the underlying pathology.

  • Imaging studies are of immense help in reaching a diagnosis,
    • CT scan of brain
    • MRI of brain
    • Chest X-Ray
    • Carotid ultrasound scan
    • Carotid MRA
  • Topical apraclonidine test
    • In Horner’s syndrome | In affected eye – After apraclonidine administration
      • Mydriasis
      • Eye lid elevation
    • In normal eye – After apraclonidine administration
      • No response
  • Topical cocaine test
    • In Horner’s syndrome | In affected eye – After cocaine administration
      • Poorly dilates the pupil
    • In normal eye – After cocaine administration
      • Mydriasis
  • Topical hydroxyamphetamine test
    • Horner’s syndrome with intact postganglionic fibers / Normal eye
      • Pupil dilate to normal size or mydriasis
    • Horner’s syndrome with damaged postganglionic fibers
      • Do not dilate the pupil
  • Haematological tests – To diagnose above causes


There is no specific treatment for Horner’s syndrome itself, rather the treatment depends on the underlying pathology.

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Adilah Efah
Adilah Efah
1 year ago

This was very useful for me. 👍
Eid Mubarak

Wilson Adler
Wilson Adler
1 year ago

i was struggling to understand this. Vividly described