• Clinical science

Horner syndrome (Oculosympathetic paresis)


Horner syndrome (HS) is a neurological disorder characterized by a symptom triad of miosis (an abnormally small pupil), partial ptosis (drooping of the upper eyelid), and facial anhidrosis (absence of sweating). This condition results from lesions that interrupt the sympathetic nervous supply to the head, eye, and neck. Most cases of HS are idiopathic, but conditions such as brainstem stroke, carotid dissection, and neoplasm are occasionally identified as the cause of HS. Because of the wide array of possible causes, diagnosis of the underlying disorder frequently poses a challenge and requires a systematic approach. Once the lesion has been identified, treatment should be tailored to the specific cause.


Type Anatomical trajectory Typical lesion


Hypothalamus (first neuron) brainstem, cervical, and thoracic spinal cord → ciliospinal center (C8–T2)


Ciliospinal center (second neuron) → pulmonary apex → stellate ganglion superior cervical ganglion


Superior cervical ganglion (third neuron) → internal carotid artery and ophthalmic nerve → iris dilator muscle


Clinical features

  • Triad of Horner syndrome
    • Ipsilateral miosis (constriction of the pupil)
    • Partial ptosis (drooping of the upper eyelid)
    • Anhidrosis or reduced sweating on the face and arm, depending on the location of the lesion
      • Presents with central and preganglionic lesions.
      • Anhidrosis; is usually absent in postganglionic lesions, but anhidrosis of the forehead could be seen in some patients if terminal branches of the internal carotid nerve, which supply sweat glands of this region, are compromised.
  • (Apparent) enophthalmos
  • Atrophy of arm and hand muscles
  • Facial flushing due to vasodilatation

Remember the symptoms of Horner syndrome by the great HORNs of the PAMpas deer: Ptosis, Anhidrosis, and Miosis.