Why Does Horner’s Syndrome Cause Ptosis?

Horner’s syndrome is a medical condition that causes abnormal symptoms in the face and eyes due to injury in the sympathetic trunk. Its impact is usually observed on one side of the face. Its causes involve tumors, damage anywhere in the pathway of the sympathetic nervous system. However, they are not identified in some cases. Its symptoms include light-colored iris, lack of redness in one of the eyes, ptosis, sweating on the one side of the face, and many more.

Why Does Horner’s Syndrome Cause Ptosis?

Horner’s syndrome is a rare condition that arises due to disruption in the pathways of nerves coming from the brain to the face. It can affect anyone at any age. It is also known as oculosympathetic palsy or Bernard-Horner syndrome. It most commonly involves the eye.(1)

The common cause of pupils is the loss of sympathetic nerve supply to the pupil occurring when the pupil is constricted. But in Horner’s syndrome, ptosis appears due to the dilatation of the pupil. The main reason behind the drooping of eyelids is the loss of nerve supply to the sphincter papillae. It is usually mild or partial and often not noticeable in this syndrome.(2)

Horner’s syndrome happens due to the disruption of the sympathetic nerve supply to the eye. It is characterized by a triad of symptoms-

Partial Ptosis – it means partial drooping of the upper eyelid.

Miosis- pupillary constriction leads to anisocoria represented by the difference in the size of the pupils.

Hemifacial Anhidrosis – it means the absence of sweating on one of the sides of the face.(3)

The cause of Horner syndrome is the damage to a particular pathway in the sympathetic nervous system. The sympathetic nervous system is responsible for regulating heart rate, pupil size, perspiration, blood pressure, and other functions. It plays a vital role in adapting according to changes in the environment.

The nerve pathway involved in Horner syndrome is categorized into three groups of nerve cells (neurons).

First-Order Neurons- This neuron pathway connects the hypothalamus at the base of the brain and the upper portion of the spinal cord, passing through the brainstem. Problems arising in this region affect the nerve function are-

  • Stroke
  • Tumorous growth
  • Diseases damaging the protective sheath on neurons (myelin)
  • Trauma in the neck
  • Cyst or cavity in the spinal cord (syringomyelia)

Second-Order Neurons- This neuron path connects the spinal column to the upper part of the chest and the side of the neck. The nerve damage in this region is caused by:

  • Lung cancer
  • Damage in the aorta
  • Tumor in the myelin sheath (schwannoma) of the nerve cells
  • Surgery in the chest cavity
  • Traumatic injury to the back

Third-Order Neurons- This neuron path connects the side of the neck and to the facial skin and muscles of the iris and eyelids. Nerve damage in this region is caused by the following:

  • Injury to the carotid artery along the side of the neck
  • Injury to the jugular vein in the side of the neck
  • Tumor or infection happening near the base of the skull
  • Migraines
  • Cluster headaches, a disorder that appears in cyclic patterns

In Children, the most common causes of Horner syndrome in children involve:

  • Injury or trauma to the neck or shoulders of the infants during delivery
  • Defect of the aorta present at birth (congenital)
  • Tumor appearing in the hormonal and nervous systems (neuroblastoma)

In most cases, the cause of Horner syndrome cannot be understood. In such a condition, it is known as idiopathic Horner syndrome.

Conclusion

Horner’s syndrome is caused due to the disruption of the sympathetic nerve pathways from the brain to the face. It leads to constriction of the pupil resulting in the dilatation of the pupil. It causes drooping of eyelids i.e., ptosis as nerve supply to the sphincter papillae is disrupted.

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