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      • Superficial ulcer
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horners

Horner’s Syndrome
 
Horner’s syndrome is a condition seen in dogs, cats, horses and cattle. It affects the eye and some of the muscles around the eye. It is caused by interruption of the sympathetic nervous system to the eye.
 
Sympathetic Nervous System
The autonomic nervous system has great control over our bodies.  There are 2 major branches: the parasympathetic branch and the sympathetic branch. The parasympathetic branch operates during relaxation ("rest and digest") and the sympathetic branch operates during times of stress ("fight or flight").
 
Sympathetic control of the eye:
  • Opens (dilates) the pupil
  • Gives tone to smooth muscle in the upper eyelids helping them to be held up
  • Gives tone to the muscles behind the eye to push it to a frontal position
  • Gives tone to smooth muscle in the third eyelid resulting in it being pushed down (the globe in frontal position also does this)
Symptoms of Horner’s syndrome are opposite to this because the sympathetic branch is NOT FUNCTIONING
 
Clinical signs of Horner’s syndrome:

Dog                                                                 Cat                                                                Horse
Pupil constriction                                            Pupil constriction                                         Pupil constriction slight
Prominent third eyelid                                    Prominent third eyelid                                 Third eyelid slightly raised
Globe sunken into the orbit                           Globe sunken into the orbit                         Globe sunken in
Drooping of the upper eyelid                         Drooping of the upper eyelid                      Drooping of the upper eyelid
                                                                                                                                               Sweating on the neck

Pathway of the Sympathetic Branch of the Autonomic Nervous System:
The nerve starts in the hypothalamus and midbrain, travels down to the mid thoracic spine, through the chest, up the neck, through the middle ear and finally to the back of the eye. 

 
Pharmacological Testing

Lesion location                                                         Time to resolution
Post-ganglionic (3rd order)                                       <15 minutes
Pre-ganglionic (2nd order)                                        20-40 minutes
1st order neuron                                                       >45 minutes or not at all
 
Phenylephrine testing is only a guide to determining where a lesion may be.  In certain cases further workup or neurological assessment with MRI may be required.
 
Breed predisposition
At Melbourne EyeVet most cases of Horner’s syndrome are seen in Golden Retrievers.  Other commonly affected breeds are Collies and Cocker Spaniels.  Diabetic patients also have a predisposition to developing Horner's syndrome.
 
Treatment for Horners
There is no actual treatment for Horner’s.  Most cases are idiopathic meaning a cause cannot be found.  In the majority of patients the symptoms resolve on their own over 6-8 weeks.  If the third eyelids are very prominent and causing a reduction in vision, phenylephrine drops can be given for the time the dog is active.


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