Horner's Syndrome

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Horner’s syndrome\: results from a lesion of the sympathetic chain supplying the eye.
Structures innervated\: Dilator pupillae (pupil dilation), superior tarsal muscle (upper eyelid elevation), sweat glands.
Triad of symptoms\: ptosis (drooping eyelid), anhidrosis (lack of sweating), and miosis (constricted pupil) on the ipsilateral
side.
Classi
First-order (central) Horner's\: lesion from hypothalamus to T1 spinal cord segment; causes include multiple sclerosis, brain
tumours, and strokes (e.g., Wallenberg’s syndrome).
Second-order Horner's\: lesion from spinal cord to superior cervical ganglion; causes include Pancoast tumours, thyroid
malignancies, iatrogenic, and traumatic causes.
Third-order (postganglionic) Horner's\: lesion from superior cervical ganglion to the eye; causes include carotid artery
dissection, cavernous sinus thrombosis, and cluster headaches.
Congenital Horner's\: present at birth, often from unknown causes or birth trauma, associated with iris heterochromia.
Investigations\: guided by systemic features; imaging (e.g., chest X-ray for Pancoast tumour), pharmacological tests with
apraclonidine (con
Management\: depends on the underlying cause; timely and accurate investigation is crucial for reducing morbidity and
mortality.
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A comprehensive topic overview

Introduction

Horner’s syndrome results from a lesion of the sympathetic chain supplying the eye.
The sympathetic nervous system innervates three important structures in the eye\:
Dilator pupillae\: involved in mydriasis or dilation of the pupil
Superior tarsal (or Muller’s) muscle\: aids in elevating the upper eyelid with the levator palpebrae superioris
Sweat glands
Horner's syndrome is characterised by the triad of ptosis (drooping eyelid), anhidrosis (lack of sweating) and miosis
(constricted pupil) on the ipsilateral side (Figure 1).
1
Figure 1. Left-sided Horner's syndrome
with ipsilateral ptosis and miosis.
3
Horner’s can arise an isolated injury or as a manifestation of a systemic disease process.
2This article will cover the classi

Classi

Horner’s can be classi
involved in Horner’s consists of three consecutive neurons, which transmit signals from the hypothalamus to the eye.
The
A useful way to di
Anhidrosis of face, arm and trunk\: central/
Anhidrosis of face\: second-order
No anhidrosis\: third-order
First-order (central Horner's)
The
Lesions arising between these positions are known to cause 'central' Horner’s syndrome and result from a variety of
pathologies such as multiple sclerosis and brain tumours.
4
Stroke can also cause central Horner’s and can present alongside other cranial nerve palsies. The most common stroke
syndrome is Wallenberg’s (lateral medullary) syndrome a
presents as Horner’s with ipsilateral ataxia, dysphagia, hoarseness and reduced gag re
5
Second-order
The second-order neuron leaves the spinal cord and travels towards the head via the cervical sympathetic chain. It
terminates at the superior cervical ganglion where it synapses with the postganglionic neuron. Shortly after exiting the
spinal cord, the neuron is in close proximation to the upper lobe of the lung and subclavian artery.
Therefore, causes of second-order Horner’s include Pancoast tumours (apical lung cancer), thyroid malignancies,
iatrogenic and traumatic causes.
2,4
Third-order (postganglionic)
The third-order (postganglionic) neuron arises from the superior cervical ganglion and travels alongside the internal
carotid artery to the cavernous sinus, where the sympathetic
Some of these
Causes of postganglionic lesions include carotid artery dissection, cavernous sinus thrombosis and rarely cluster
headaches.
2,4
Congenital
Very rarely, Horner’s can be present at birth, commonly from unknown causes or secondary to birth trauma. The classic

2
Figure 2. Iris heterochromia.
6Investigations
The presence of systemic features with Horner’s can help guide the identi
investigations. For example, patients with cough and weight loss should undergo a chest X-ray to screen for a Pancoast
tumour.
For unclear cases, Horner’s can be diagnosed pharmacologically using eye drops.
Classically, cocaine eyedrops were used to con
Apraclonidine is now the commonly used alternative to con
Horner’s due to its agonistic e
Hydroxyamphetamine drops can subsequently be used to identify the location of the lesion to guide imaging.
Hydroxyamphetamine will dilate a constricted Horner’s pupil if there is an underlying preganglionic lesion (
second-order).
If the pupil fails to dilate, this suggests that the lesion is in the third order or postganglionic neuron.
2

Management

Like investigations, the management of Horner’s depends on the underlying cause. Accurate and timely investigation of
sudden-onset Horner’s aids in reducing morbidity and mortality of patients.
1

References

MSD Manuals. H o r n e r’ s s y n d r o m e . September 2021. Available from\: [LINK]
EyeWiki. H o r n e r’ s s y n d r o m e . Updated in 2021. Available from\: [LINK]
Waster. M i o s i s . License\: [CC BY]. Available from\: [LINK]
Kanagalingam S. H o r n e r s y n d r o m e \: c l i n i c a l p e r s p e c t i v e s . Eye Brain. 2015; Liu F, Tadi P, Anilkumar A. W a l l e n b u r g S y n d r o m e . Available from\: [LINK]
EyeMD. H e t e r o c h r o m i a i r i d i s . License\: [CC BY-SA]. Available from\: [LINK]
7\: 35–46.

Reviewer

Consultant Ophthalmologist

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