7.8  Horner's Syndrome

A Horner’s syndrome arises from pathology in the sympathetic innervation of the eye. The two main clinical features are anisocoria and ptosis- the candidate may be directed to examine pupils or eyelids, although it is more common to request the pupillary examination. Once a Horner’s syndrome is diagnosed, associated signs should be sought that will assist with localising the lesion (to central, pre-ganglionic and post-ganglionic).

Examination Outline


1. Central

  • Hypothalamus → Ciliospinal centre of Budge (C8-T2)
  • Brainstem CVA (e.g. Lateral medullary syndrome), tumour, MS
  • Cervical Syringomyelia

2. Pre-ganglionic

  • Ciliospinal centre of Budge (C8-T2) → Superior cervical ganglion
  • Cervical sympathectomy
  • Thyroid cancer
  • Pancoast tumour

3. Post-ganglionic

  • Superior cervical ganglion → Eye
  • Internal carotid artery dissection
  • Cavernous sinus syndrome

4. Paediatric Horner’s

  • Cardiac (VSD), Birth trauma, Neuroblastoma
Figure 7.8.1 Oculo-sympathetic Pathway

Figure 7.8.1
Oculo-sympathetic Pathway

A Horner’s Syndrome may be central (red), pre-ganglionic (blue) or post-ganglionic (green).

Examination Structure

“Please examine this patient’s pupils”

Section 7.7 Pupils should be read in conjunction with this page.

1. Visual Acuity (Best Corrected)

2. Inspection (Spectacles Off)

i. Pupil Size (Anisocoria)
ii. Pupil Shape
iii. Heterochromia Iridis
  • The affected side is lighter. Only present in congenital or early acquired Horner’s syndrome. If present in an adult with incidentally noted Horner’s Syndrome, further investigation for sinister neurological causes is unnecessary
iv. Eyelids
  1. Ptosis (paralysis of Müllers muscle)
  2. Inverse ptosis (lower lid elevation in Horner’s)
v. Strabismus (CNIII palsy)

Scars (neck scar with Horner’s, tracheostomy scar with previous trauma)

3. Measure Pupils in Light then Dark

  • Anisocoria worse in dark = Problem with the smaller pupil (not dilating)
  • It is important to measure the pupils quickly once the room lights have been turned off. Patients with Horner’s syndrome have a dilatation lag - the affected pupil will dilate, but more slowly by passive relaxation of the sphincter pupillae alone (compared to the fellow eye with intact dilator pupillae activity)

4. Direct and Consensual Pupillary Light Reflexes

  • Normal pupillary light reflexes

5. Relative Afferent Pupillary Defect (RAPD)

  • No RAPD
Figure 7.8.2 Left Horner’s Syndrome

Figure 7.8.2 Left Horner’s Syndrome
Left ptosis and miosis

Additional Clinical Signs to Look for to Localise the Lesion

1. Anhidrosis

  • Found only in central / preganglionic lesions proximal to the carotid artery bifurcation since sweat glands are supplied by external carotid artery sympathetics)

2. Neck

  • Palpate in supraclavicular fossa, and check thyroid gland while asking patient to swallow, and look for scars
  • Scar (Cervical sympathectomy)
  • Thyroid cancer
  • Supraclavicular lymphadenopathy (Pancoast tumour)

3. Hands

  • Wasting / weakness (T1) – check for finger abduction by asking the patient to fan out their fingers against resistance
  • Clubbing (Pancoast tumour), claw (Cervical cord)

4. Eye Movements

Check carefully for an ipsilateral minor abduction weakness or slowed abducting saccade CV VI (cavernous sinus)

5. Auscultate

  • Carotid bruit? (Internal carotid artery dissection)
  • Respiratory exam (Pancoast tumour)

6. Other Neurological Signs

  • Brainstem CVA (e.g. Lateral medullary syndrome), tumour, MS, Cavernous sinus syndrome
  • Ipsilateral hemisensory loss pain / temperature (Lateral medullary syndrome)
  • Ask the patient to say “Ah!” and check gag reflex CN IX (Lateral medullary syndrome)
Limb Exam
  • Contralateral hemisensory loss pain / temperature (Lateral medullary syndrome)
  • Past pointing, Ataxia (Lateral medullary syndrome)
  • Ask the patient to say “British Constitution”
  • Hoarse? CN X Recurrent laryngeal nerve palsy (Pancoast tumour)
  • Cerebellar dysarthria? (Lateral medullary syndrome)

7. Check Old Photos to See if the Horner’s Syndrome is Acute

Figure 7.8.3 Long Standing Right Horner’s Syndrome

Figure 7.8.3
Long Standing Right Horner’s Syndrome

This patient has ptosis, miosis and slight heterochromia.

Pharmacological Testing

  • This is less commonly performed now since imaging (CT chest, MRI / MRA brain / neck) can localise most lesions. However it is important to be familiar with these techniques as they are still used in difficult cases. This area remains a common examination topic





Cocaine 10%
Will NOT dilate Horner’s


Apraclonidine 1%
Will ABNORMALLY dilate Horner’s



Hydroxyaphetamine 1%
Will NOT dilate post ganglionic Horner’s


Phenylepherine 1%
Will ABNORMALLY dilate post ganglionic Horner’s

1. Apraclonidine 1% (For Diagnosis)

  • Weak dilating effect that is enhanced in Horner’s pupil due to denervation super-sensitivity
  • Will reduce the ptosis in 15 minutes and reverse the anisocoria (dilates the Horner’s pupil) in 30-45 minutes. Beware of using this in infants (as it can cause drowsiness)
Figure 7.8.4 Reversal of Signs in a Right Horner’s Syndrome Post Apraclonidine

Figure 7.8.4
Reversal of Signs in a Right Horner’s Syndrome Post Apraclonidine

Same patient as in Figure 7.8.3, 45 minutes post apraclonidine with reversal of anisocoria. Note the improvement of the ptosis and the reversal of the miosis.

2. Cocaine 10% (For Diagnosis)

Prevents noradrenaline reuptake dilating a normal pupil.

  • This drop is difficult to obtain (use apraclonidine as an alternative) but is occasionally necessary (particularly in infants where apraclonidine is contraindicated). It will not dilate a Horner’s pupil because noradrenaline is not being released. This drop stings - give local anaesthetic prior! Ensure that patient is active after drop instillation, not resting, as that may cause a false negative result
  • Check the pupils in the dark after 30 minutes. If the pupil does not dilate, check that the pupil can dilate with 10% phenylephrine to exclude other causes of miosis (e.g. posterior synechiae). A Horner’s pupil should dilate with 10% phenylephrine

3. Phenylephrine 1% (To Localise)

  • Weak dilating effect that is enhanced in post-ganglionic Horner’s pupil due to denervation super-sensitivity
  • This will dilate a post-ganglionic Horner’s pupil due to denervation super-sensitivity but will not dilate a normal pupil or a pre-ganglionic Horner’s pupil. This is much easier to obtain than hydroxyamphetamine. 1% phenylephrine solution can be prepared in the clinic by diluting 4 drops of 2.5% phenylephrine with 6 drops of normal saline

4. Hydroxyamphetamine 1% (To Localise)

  • ↑ release of stored synaptic noradrenaline
  • This drop is difficult to obtain. It will not dilate postganglionic lesions because noradrenaline is not stored in damaged postganglionic neurons. Do not test within 24 hours of the cocaine test or 7 days of onset (false negatives)

7.7  Pupils


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