You may be referred back to your veterinarian for evaluation of systemic disease or a close examination of the ear canal. Third order Horner’s syndrome is the most commonly seen form in dogs and is most often associated with inner or middle ear disease. Patients with Second order Horner’s syndrome might have thoracic disease, including tumors within the chest cavity or neck trauma. Studies also have demonstrated a correlation between endocrine diseases, like hypothyroidism or Cushing’s disease, in patients with Horner’s syndrome. For example, patients with First order Horner’s syndrome may have a history of brain or spinal cord trauma. Determining the location of the damage is important because it may help to uncover the cause of the damage or other problems in that area. This usually takes about 15 to 30 minutes. To try 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. Damage between the base of the skull and eye is called Third order Horner’s syndrome.Damage between the chest cavity and the base of the skull is called Second order Horner’s syndrome.Damage within the brain and spinal cord is called First order Horner’s syndrome.Determining the Location of the Damageĭamage can occur anywhere along the nerve pathway: Damage to this nerve anywhere along its path results in loss of sympathetic innervation leading to the characteristic signs listed above. Inside the orbit, it branches to innervate certain structures of the eye. 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. The second section of the nerve travels up the neck to the base of the skull. The nerve exits the spinal cord in the area near the shoulders and then travels through the chest cavity. The first section of the nerve then travels down the neck within the spinal cord. The sympathetic nerve supply to the eye originates at the base of the brain and has 3 sections. It also controls the fight or flight response. The sympathetic nervous system is part of the autonomic nervous system that “automatically” controls a variety of bodily functions, including pupil size, without conscious effort. These symptoms are not painful though they may interfere with vision due to the third eyelid elevation. A sunken appearance of the eye (enophthalmos).A constricted pupil that does not dilate (miosis).These particular clinical signs seen with Horner’s occur due to damage to the sympathetic nerve supply to the eye: The lens is behind the pupil but is not seen when healthy, as it is clear.Horner’s syndrome is a collection of clinical signs that are seen together and often have a limited number of causes. The pupil is a hole in the center of the iris. The pupils should be the same size and should constrict to a pinpoint when a bright light is shined in the eye. The pupil is the black spot in the center of the eye.
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