The Swiss doctor Johan Friedrich Horner (1831 – 86) described in 1869 a 40-year-old woman who had a headache and who was red, dry and hot in the right half of the face. It seemed as if her right eye was a little sunken and in addition she had slightly drooping eyelids and anisokoria with the least pupil on this side. Horner concluded that the symptom complex must be due to a paralysis of the sympathetic fibres on the neck. This immortalized his name, but it should be mentioned that the French physiologist Claude Bernard (1813 – 1878) had already in 1852 described a similar syndrome in guinea pigs that were cut over sympathetic fibers on the neck, and that Silas Weir Mitchell (1829 – 1914) in 1864 described an isolated Horner triad in a 24-year-old soldier with a gunshot wound to the neck.
Central (1st-order neuron) Horner syndrome:
1st-order neurons are located in the posterolateral hypothalamus, and from there, sympathetic fibers pass through the lateral brain stem and extend to the ciliospinal center of Budge & Waller in the intermediolateral gray column of the spinal cord at C8–T1
Central Horner syndrome caused by damage to any of these structures is ipsilateral to the lesion:
Preganglionic (2nd-order) sympathetic neurons exit from the ciliospinal center of Budge and Waller and pass across the pulmonary apex. They then ascend through the stellate ganglion and up the carotid sheath to synapse at the superior cervical ganglion, located at the level of the bifurcation of the common carotid artery and the angle of the jaw.
eg. Pancoast tumour (Bronchogenic carcinoma of the superior fissure on apex of lung)
Postganglionic (3rd-order) sympathetic neurons originate in the superior cervical ganglion, travel in the wall of the internal carotid artery, and continue on to the cavernous sinus. Within the cavernous sinus, the fibers briefly travel with the abducens nerve before joining the ophthalmic division of the trigeminal nerve and entering the orbit with its nasociliary branch (Figure 3A and B). The sympathetic fibers in the nasociliary nerve divide into the two long ciliary nerves that travel with the lateral and medial suprachoroidal vascular bundles to reach the anterior segment of the eye and innervate the iris dilator muscle.
eg. Carotid dissection (painful)
C/F: No anhidrosis
Bilateral Horner syndrome:
Associated systemic disorders:
Diabetic autonomic neuropathy
Pure autonomic failure
Classic Horner’s syndrome triad:
Ptosis (slight drooping of eyelid: muller muscle palsy)
Anhidrosis (absence of sweating) and flushing of affected side of face
Miosis (pupil constriction)
Upside down ptosis
Enophthalmos (sunken eyeball)
Hypochromic heterochromia iridis (lighter colored iris in abnormal eye; seen only in congenital Horner’s syndrome)
Cocaine acts an indirect sympathomimetic inhibiting the reuptake of norepinephrine from the synaptic cleft. Cocaine solution (ranging from 2% to 10%) is instilled into both eyes. Both eyes are evaluated after at least 30 or more minutes for an optimal response. Denervation in the affected eye causes it to dilate poorly compared to the normal one. Anisocoria of 0.8 mm or more is considered diagnostic.
Detect presence of HS
The test does not help in identifying the level of lesion.
Two drops of 1% hydroxyamphetamine solution are instilled into both eyes. The affected eye (third-order lesion) will not dilate as well as the normal eye. While in the case of intact postganglionic fibers (first and second-order lesions), the affected pupil dilates to an equal or greater extent.
Localization of the lesion (hydroxyamphetamine stimulates the release of stored norepinephrine from the postganglionic terminals into the synapse. Postganglionic third-order lesions can be differentiated from presynaptic second-order or first-order ones.)
Topical apraclonidine test:
TEST OF CHOICE due to good sensitivity and overall practicality. Apraclonidine acts as a weak α1-agonist and strong α2-agonist. It is categorized as an ocular hypotensive agent. The upregulation of α1-receptors in Horner syndrome translates into an exaggerated response of the iris dilators (denervation supersensitivity) to an agonist agent like apraclonidine. A 0.5-1% solution is instilled in both eyes. The affected eye will show mydriasis, while the normal eye is predominantly insensitive. Consequent instillation of the solution results in evident reversal of anisocoria (the affected pupil dilates and the normal pupil constricts). This is because of the stronger α2-agonist activity of compared to the weaker α1-agonist activity of apraclonidine.
Physiological anisocoria (in 20% of the normal population)