Mydriasis associated with local dysfunction of parasympathetic nerves in two dogs

In clinical practice, photophobia resulting from persistent mydriasis may be associated with dysfunction of ocular parasympathetic nerves or primary iris lesions. We encountered a 5-year-old Miniature Dachshund and a 7-year-old Shih Tzu with mydriasis, abnormal pupillary light reflexes, and photophobia. Except for sustained mydriasis and photophobia, no abnormalities were detected on general physical examination or ocular examination of either dog. We performed pharmacological examinations using 0.1% and 2% pilocarpine to evaluate and diagnose parasympathetic denervation of the affected pupillary sphincter muscles. On the basis of the results, we diagnosed a pupillary abnormality due to parasympathetic dysfunction and not to overt primary iris lesions. The test revealed that neuroanatomic localization of the lesion was postciliary ganglionic in the first dog.