Horner’s syndrome, also known as oculosympathetic palsy or oculosympathetic paresis, is a rare condition of the nervous system impacting the eyes, that can affect people of all age groups. It refers to a combination of symptoms that develop due to impairment of a cluster of nerves called as the sympathetic trunk, along one side in the upper body.

The sympathetic trunk comprises nerves that begin at the spinal cord in the chest, ascending all the way up to the neck, face and eyes. They form a part of the sympathetic nervous system, which is a sub-category of the autonomic or involuntary nervous system.

This neural network performs vital roles such as monitoring rate of heartbeat, pupil size, perspiration and blood pressure, besides other activities that enable the body to adapt to modifications in the external surroundings. Hence, substantial injury to the sympathetic trunk as is the case in Horner’s syndrome results in reduced size of the pupil lowered rate of sweating, as well as a sagging eyelid.

Horner's syndrome

Horner’s syndrome is named after the renowned Swiss ophthalmologist, Johann Friedrich Horner, who first discovered and outlined this rare disorder in the year 1869.

Since various factors can cause Horner’s syndrome in people, there is no specific treatment for this illness. However, identifying the exact aspects of triggering Horner’s syndrome in the affected individual can help to rectify the underlying health anomalies and restore normal nerve function.


The sympathetic trunk, which undergoes significant damage in the case of Horner’s syndrome, is classified into three distinct segments of nerve cells or neurons based on where and how the ailment occurs, as:

First-Order Neurons:

This grid of nerve cells starts at the hypothalamus situated in the base of the brain, goes through the brainstem and stretches into the upper portion of the spinal cord. The different circumstances in which Horner’s syndrome can befall a person in this location include:

  • Stroke
  • Tumour
  • Diseases that result in loss of myelin sheath – the protective layer enveloping neurons
  • Trauma to the neck
  • Cyst or cavity in the spinal column i.e. syringomyelia

Second-Order Neurons:

This neuronal pathway ranges from the spinal column, across the upper chest region and up until the side of the neck. The possible causes of a decline in nerve function in this segment comprise:

Third-Order Neurons:

This complex mesh of nerve cells begins at the side of the neck and reaches up to the facial skin, as well as muscles of the iris and eyelids. Damage to nerves in this portion of the sympathetic trunk happens due to:

In Children:

In a majority of cases, Horner’s syndrome in children stems from the following reasons:

  • Lesions to the neck or shoulders during delivery
  • Faults in the aorta at the time of birth
  • Tumours in the neuroendocrine system, like neuroblastoma

Unknown Causes:

The precise cause of Horner’s syndrome cannot be determined in certain situations. This is termed as idiopathic Horner syndrome.


In Adults:

The characteristic signs of Horner’s syndrome in adults are quite challenging to detect and consist of:

  • The pupil in the eye constantly being of small size i.e. miosis
  • The prominent difference in the size of pupils in both eyes i.e. anisocoria
  • The decreased response of pupils to dim light
  • Drooping of the upper eyelid i.e. ptosis
  • Heightened presentation of the lower eyelid i.e. upside-down ptosis
  • Hollow look of the eye
  • Little to no sweating on the entire face or a patch of the skin i.e. anhidrosis

In Children:

The distinct indications of Horner’s syndrome in children include:

  • Very light colour of the iris, in the affected eye, below the age of one year
  • Absence of redness or flushing, even upon contact with heat and other physical forces, on the affected side of the face

Diagnosis And Treatment

The eye doctor or ophthalmologist primarily conducts a physical exam to detect any underlying condition that might be the basis behind Horner’s syndrome in the patient. He or she then tests the dilation or constriction of pupils, by introducing medicated eye drops in both the eyes. In case the pupil response in one of the eyes is not normal, underlying nerve damage is considered as the most likely explanation and further tests are conducted, to locate the particular site of nerve damage.

Aberrations in nerve transmission in one side of the upper body observed in Horner’s syndrome, can be visualized by means of advanced imaging analysis. These include MRI tests, CT scans and Carotid Ultrasounds, in addition to Chest X-rays.

Once the actual site of injury in the nerves has been pinpointed, doctors initiate treatment procedures to mend the malfunctioning in the sympathetic nervous system. There is no actual treatment for Horner’s syndrome. Correcting the flaws in the neural network helps to alleviate all symptoms of discomfort to the eye as well as regain optimal nerve functions by the patient, to ensure a complete recovery.