Horner's syndrome is a eye disorder that consists of enophthalmos (sinking of the eyeball into its cavity), ptosis (droopy upper eyelid), swelling of the lower eyelid, miosis (abnormal contraction of the pupil), anhidrosis (absence of facial sweat) and heterochromia (difference in eye color).
Horner's syndrome is caused by paralysis of the cervical sympathetic nerves.
To better understand Horner's syndrome, one needs to understand how the nervous system works.
There are two major divisions within the nervous system. There is the part of the nervous system that you are aware of and have control over, and there is a part of the nervous system that is under automatic control, called the autonomic nervous system.
Within the autonomic nervous system there are two divisions, the sympathetic and the parasympathetic nervous systems.
The sympathetic nervous system controls many of the involuntary activities of the glands, organs and other body parts. The parasympathetic nervous system also controls the involuntary activities of the organs, glands as well as blood vessels and other tissues in the body.
The eye has both sympathetic and parasympathetic function (innervation). If something were to block the sympathetic impulses into the eye, there would be an overbalance of parasympathetic supply to the eye. The result is Horner's syndrome.
The nervous system in the body does not consist of straight lines to and from the brain. In respect to the eye, the sympathetic nerves travels from the brain down the spinal column to the chest area and back up.
The first part of the journey, called the first neuron pathway, starts at the brain and travels down the spinal cord and into the chest.
The second neuron pathway continues from the chest cavity, over the lungs and up the carotid artery in the neck.
The third neuron pathway goes from the carotid artery and jugular vein through the middle ear and then into the eye.
Upon entering the eye the nerve pathways split, one goes to the pupil and one goes to the muscles of the eyelid. Horner's syndrome may occur as a result of lesions found along the course of the nerve's route from the brain to the eye.
There are three major types of Horner's syndrome. Each named after its pathway (first, second, or third) and associated with the parts of the body within the pathway (central, preganglionic, and postganglionic).
First Neuron Horner's Syndrome (central lesions) can be caused by the occlusion (closure) of the posteroinferior cerebellar artery at the lower portion of the brain stem (also known as Wallenberg syndrome), by a transient ischemic attack (brief interruption of the blood supply to the brain), or by brain tumors.
Second Neuron Horner's Syndrome (preganglionic lesions) may be caused by lung cancer, thoracic tumors, phrenic nerve syndrome, thyroid enlargement, severe osteoarthritis of the neck with bone spurs, spinal cord injury or disease, neck trauma caused by injury, surgery, or severe whiplash.
Third Neuron Horner's Syndrome Group II involves the facial sweating mechanism.
When Horner's syndrome occurs for no apparent reason, it may be been inherited or caused by viral, immune-mediated or idiopathic (without recognizable cause) neuropathies.
The symptoms of Horner's syndrome include:
- Drooping of the upper eyelid
- Swelling of the lower eyelid
- Sinking of the eyeball
- An absence of sweat on the same side of the face as the affected eye
- The pupil becomes smaller (miotic)
- Each iris may be a different color
For proper diagnosis of Horner's syndrome, the physician will conduct a thorough medical history (emphasizing past injuries and surgeries) and examine the patient's neck, thyroid, and lymph nodes for other non-Horner's conditions.
Additionally a chest x-ray, blood analysis, and eye examination will be done.
The ocular examination may consist of a pupillograph. This test examines the absolute and relative size and reaction of the pupil to both light/dark and accommodation. When observed in room light, the anisocoria (inequality of pupil size) in Horner's syndrome may be as little as 1 mm or even less. In darkness, the anisocoria is increased and the effected pupil dilates more slowly than normal.
Pharmacologic tests involve administering phenylephrine, epinephrine, or hydroxyamphetamine to the suspected pupil and watching its reaction to these dilation drugs.