Idiopathic Horner's syndrome in collie dogs.

Seven cases of idiopathic Horner's Syndrome in the Collie are described. Five males and two females presented with unilateral miosis, ptosis of the upper eyelid, enophthalmos and protrusion of the third eyelid. Thorough examination, pharmacological testing with phenylephrine, complete blood counts and radiography of the tympanic bullae and thorax were performed. The etiology was not identified in any of the cases. Clinical signs improved with pharmacologic testing within 20-40 min. In five dogs, total resolution of clinical signs was observed at 4 and 16 weeks after their initial appearance. Pharmacological testing suggested that the deficit could be at the preganglionic neuron.