Horner’s Syndrome
General information
Horner’s syndrome is due to a loss of proper innervation of the nerves which supply the eye. Horner’s syndrome causes a complex of four particular clinical signs which leads to the affected eye looking very different from the un-affected, or normal, eye.
Causes
There are many things which can affect the proper nerve pathways to the eye and lead to Horner’s syndrome. Ear infections which affect the middle ear are a common cause of Horner’s syndrome in cats. Lymphosarcoma causing masses in the chest of cats can affect nerve branches and lead to Horner’s syndrome. Injuries or masses of the spinal cord or its branches, injury or masses behind the eye, and injury or masses of the head are all other possible causes of Horner’s syndrome. In almost 45% of the cases of Horner’s syndrome in cats, the cause is determined to be idiopathic, which means we do not know what the underlying cause is.
Cardinal symptom
Unequal pupil size, Drooped upper eyelid, Sunken eye, Protrusion of third eyelid
Symptoms
A complex of four signs will be seen with Horner’s syndrome:
• the affected eye will retract slightly into the orbit and appear “sunken”
• the upper eyelid will droop
• the third eyelid will protrude, and
• the pupil will constrict and appear smaller than the pupil of the other eye
Diagnosis
Diagnosis of Horner’s syndrome is made based on clinical examination. To determine the underlying cause of the Horner’s syndrome, your veterinarian will perform a complete physical exam on your cat, including examination of the eyes and ears, and, possibly, a complete neurologic exam. Other diagnostic procedures, including imaging studies (such as chest x-rays or CT scans) and spinal fluid analysis, may be recommended.
Treatment
The specific treatment recommended will depend upon the underlying cause of the Horner’s syndrome. In cases of idiopathic Horner’s syndrome, no treatment is necessary and the signs will often resolve on their own after several weeks or months.
Prognosis
The prognosis varies depending upon the underlying cause, and can range from excellent (e.g., for idiopathic Horner’s or ear infections) to grave (e.g., for lymphosarcoma or other malignant tumors).