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Horner's syndrome
Classification and external resources

Left-sided Horner's syndrome
ICD-10 G90.2
ICD-9 337.9
OMIM 143000
DiseasesDB 6014
MedlinePlus 000708
eMedicine med/1029 oph/336
MeSH D006732

Horner's syndrome or Horner syndrome is a clinical syndrome caused by damage to the sympathetic nervous system. It is also known by the names Bernard-Horner syndrome or oculosympathetic palsy.



Signs found in all patients on affected side of face include; ptosis (which is drooping of the upper eyelid from loss of sympathetic innervation to the superior tarsal muscle, also known as Müller's muscle [1]), upside-down ptosis (slight elevation of the lower lid), and miosis (constricted pupil) and dilation lag (slow response of the pupil to light). Enophthalmos (the impression that the eye is sunk in) and anhydrosis (decreased sweating) on the affected side of the face, loss of ciliospinal reflex and bloodshot conjunctiva may occur depending on the site of lesion. Sometimes there is flushing of the face is on the affected side of the face due to dilation of blood vessels under the skin.

The clinical features of Horner's syndrome can be remembered using the mnemonic, "Horny PAMELa" for Ptosis, Anhydrosis, Miosis, Enophthalmos and Loss of ciliospinal reflex.[2]

In children Horner syndrome sometimes leads to a difference in eye color between the two eyes (heterochromia).[3] This happens because a lack of sympathetic stimulation in childhood interferes with melanin pigmentation of the melanocytes in the superficial stroma of the iris.


It is named after Johann Friedrich Horner, the Swiss ophthalmologist who first described the syndrome in 1869.[4][5] Several others had previously described cases, but "Horner's syndrome" is most prevalent. In France and Italy, Claude Bernard is also eponymised with the condition ("Claude Bernard-Horner syndrome").


Horner syndrome is acquired as a result of pathology but may also be congenital (inborn) or iatrogenic (caused by medical treatment). Although most causes are relatively benign, Horner syndrome may reflect serious pathology in the neck or chest (such as a Pancoast tumor (tumor in the apex of the lung) or thyrocervical venous dilatation).


Horner syndrome is due to a deficiency of sympathetic activity. The site of lesion to the sympathetic outflow is on the ipsilateral side of the symptoms. The following are examples of conditions that cause the clinical appearance of Horner's syndrome:

  • First-order neuron disorder: Central lesions that involve the hypothalamospinal pathway (e.g. transection of the cervical spinal cord).
  • Second-order neuron disorder: Preganglionic lesions (e.g. compression of the sympathetic chain by a lung tumor).
  • Third-order neuron disorder: Postganglionic lesions at the level of the internal carotid artery (e.g. a tumor in the cavernous sinus).

If someone has impaired sweating above the waist affecting only one side of the body, yet they do not have a clinically apparent Horner's syndrome, then the lesion is just below the stellate ganglion in the sympathetic chain.


Three tests are useful in confirming the presence and severity of Horner syndrome:

  1. Cocaine drop test - Cocaine eyedrops block the reuptake of norepinephrine resulting in the dilation of a normal pupil. Due to the lack of norepinephrine in the synaptic cleft, the pupil will fail to dilate in Horner's syndrome. A more recently introduced approach that is more dependable and obviates the difficulties in obtaining cocaine is to apply the alpha-agonist apraclonidine to both eyes and observe the reversal of miosis on the affected side of Horner syndrome (the opposite effect to cocaine).
  2. Paredrine test:- This test helps to localize the cause of the miosis. If the 3rd order neuron (the last of 3 neurons in the pathway which ultimately discharges norepinephrine into the synaptic cleft) is intact, then the amphetamine causes neurotransmitter vesicle release, thus releasing norepinephrine into the synaptic cleft and resulting in robust mydriasis of the affected pupil. If the lesion itself is of the aforementioned 3rd order neuron, then the amphetamine will have no effect and the pupil remains constricted. There is no pharmacological test to differentiate between a 1st and 2nd order neuron lesion.
  3. Dilation lag test

It is important to distinguish the ptosis caused by Horner's syndrome from the ptosis caused by a lesion to the oculomotor nerve. In the former, the ptosis occurs with a constricted pupil (due to a loss of sympathetics to the eye), whereas in the latter, the ptosis occurs with a dilated pupil (due to a loss of innervation to the sphincter pupillae). In an actual clinical setting, however, these two different ptoses are fairly easy to distinguish. In addition to the blown pupil in a CNIII (oculomotor nerve) lesion, this ptosis is much more severe, occasionally occluding the whole eye. The ptosis of Horner syndrome can be quite mild or barely noticeable.

When anisocoria occurs and the examiner is unsure whether the abnormal pupil is the constricted or dilated one, if a one-sided ptosis is present then the abnormally sized pupil can be presumed to be the one on the side of the ptosis.

See also


  1. ^ Adams, Raymond Delacy; Victor, Maurice; Ropper, Allan H. (2001). Adam and Victor's principles of neurology. New York: McGraw-Hill. ISBN 0-07-067497-3.  
  2. ^ "Medical mnemonics". LifeHugger. Retrieved 2009-12-19.  
  3. ^ Gesundheit B, Greenberg M (2005). "Medical mystery: brown eye and blue eye--the answer". N Engl J Med 353 (22): 2409–10. doi:10.1056/NEJM200512013532219. PMID 16319395.  
  4. ^ Horner JF. Über eine Form von Ptosis. Klin Monatsbl Augenheilk 1869;7:193-8.
  5. ^ synd/1056 at Who Named It?
  6. ^ Graff JM, Lee AG (February 21, 2005). "Horner's Syndrome (due to Cluster Headache): 46 y.o. man presenting with headache and ptosis.". Ophthalmology Grand Rounds. The University of Iowa. Retrieved 2006-09-22.  

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