A syndrome is a collection of symptoms that often has a limited number of causes and can thus help doctors diagnose the underlying problem. The following clinical sign collectively indicate damage to the sympathetic nerve supply to the eye, and is referred to as Horner’s Syndrome:
- A constricted pupil (miosis)
- A drooping of the upper eyelid (ptosis)
- A sunken appearance of the eye (enophthalmos)
- An elevation of the third eyelid
These symptoms are not painful, however may interfere with vision due to the third eyelid elevation.
Sympathetic Nerve Pathway to the Eye
The sympathetic supply to the eye originates at the base of the brain. The first section of the nerve then travels down the neck (with the spinal cord). The nerve exits the spinal cord in the thoracic area and then travels through the chest cavity. The second section of the nerve travels to the base of the skull. The third section of the nerve then takes an elaborate route through the skull where it is closely associated with the bone of the middle ear before finally reaching the orbit. Here, it branches to innervate the structures of the eye. Damage to this nerve results in loss of sympathetic innervation leading to the characteristic signs listed above.
Determining the Location of the Damage
Damage can occur anywhere along the nerve pathway:
- Damage within the brain and spinal cord, is called first order Horner’s syndrome.
- Damage between the chest cavity and the base of the skull, is called second order Horner’s syndrome
- Damage between the base of the skull and eye, is called third order Horner’s syndrome.
To determine the location of nerve damage, your veterinary ophthalmologist may apply eye drops that stimulate different sections of the nerve and monitor the response. Determining the location of the damage is important because it may highlight other problems in that area.
For example, patient’s with first order Horner’s syndrome may have a history of brain or spinal cord trauma. Studies also have demonstrated a correlation of endocrine diseases like hypothyroidism in patients with Horner’s syndrome. Patients with second order Horner’s syndrome might have thoracic disease, including tumors within the chest cavity or neck trauma. Patients with third order Horner’s syndrome have a higher probability of middle ear diseases.
Treatment
We can temporarily treat the symptoms of Horner’s syndrome for diagnostic purposes. To temporarily reverse the signs of Horner’s syndrome, your veterinary ophthalmologist may prescribe eye drops called sympathomimetics that mimic the sympathetic system supply.
While most patients with Horner’s syndrome do not warrant medical therapy for the eye, determining and treating the underlying cause of this syndrome is important. If detected early, the disease causing the syndrome (for example, cancer) can be treated. If left undetected for too long, the disease might prove to be irreversible or fatal.
If you have any questions regarding Horner’s Syndrome, please call us at Eye Care for Animals.
