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Today's VeTerinary PracTice | January/February 2016 | tvpjournal.com obserVaTions in oPhThalmology Peer reviewed 82 Uveitis Uveitis (intraocular infammation) can also cause anisocoria. although this can occur as a result of iridal swelling, more commonly, prostaglandins active within the eye during acute infammation act directly on the iris sphincter muscle to cause miosis. Thus, a unilateral or asymmetric uveitis can lead to anisocoria. 9 additional signs of uveitis include blepharospasm, episcleral hyperemia, deep corneal vascularization, diffuse corneal edema, aqueous fare, swollen and/or hyperemic iris, and decreased intraocular pressure. These should be assessed before a neurologic cause of anisocoria is investigated. Posterior Synechia Posterior synechia—adherence of the iris to the lens—can result in a fxed, nonmobile pupil that can either be relatively miotic, mydriatic, or abnormally shaped. Immune-Mediated or Infectious Disease immune-mediated or infectious disease can affect any portion of the central nervous system (cns), causing visual, sympathetic, or parasympathetic dysfunction in any combination. The majority of dogs with immune-mediated cns disease require immunosuppressive therapy to control their clinical signs; this, however, requires that infectious and neoplastic causes are frst eliminated. 10,11 infectious agents implicated as causes of cns disease include viruses, bacteria, fungi, protozoa, and, rarely, rickettsial infections. Treatment and prognosis varies depending on the cause of the infection. Glaucoma glaucoma (increased intraocular pressure) can cause a unilateral mydriasis. The mechanism by which mydriasis occurs in glaucoma is not entirely clear, but likely involves iris or optic nerve dysfunction associated with elevated intraocular pressure. other signs may include blepharospasm, episcleral hyperemia, deep corneal vascularization, and diffuse corneal edema. Trauma Brachial Plexus Avulsion brachial plexus avulsion is a common cause of damage to the second order sympathetic neurons between T1 and T3. brachial plexus injury commonly occurs after vehicular trauma and may result in partial or complete loss of the affected nerve roots. amputation of the affected limb may be indicated if recovery is not likely; however, ocular sympathetic dysfunction does not resolve with amputation of the limb. Head Trauma head trauma is a common cause of parasympathetic dysfunction due to compression of the midbrain at the level of the Psn cn iii. compression occurs secondary to hemorrhage or increased intracranial pressure, resulting in herniation of the brain. elevated intracranial pressure, with damage to the cerebrum or diencephalon, results in miosis due to disinhibition of the parasympathetic fbers and, possibly, damage to the sympathetic fbers. as brainstem compression occurs, miosis progresses to mydriasis with absent P lr. Prognosis is guarded when miosis is detected, and grave after mydriasis, with absent P lr, is identifed. 1 Treatment to decrease intracranial pressure should be started as soon as possible. Jugular Venipuncture Jugular venipuncture can cause anisocoria due to iatrogenic damage to the second order sympathetic neuron as it courses through the jugular groove, deep to the jugular vein. excessive probing for the vein may result in damage to this nerve. care should be exercised when attempting jugular venipuncture, Hei D i Bar N es Heller Heidi Barnes Heller, DVM, Diplomate ACVIM (Neurology), is a clinical assistant professor at University of Wisconsin–Madison. Her research interests include feline seizure disorders and the development of anti- epileptic drugs, brain and spinal cord surgery, and infammatory CNS disease. She received her DVM from Michigan State University, completed a rotating internship at University of Illinois, and completed a combined neurology and neurosurgery residency at University of Florida. e llisoN BeNTleY Ellison Bentley, DVM, Diplomate ACVO, is a clinical professor and section head of comparative ophthalmology at University of Wisconsin–Madison. Her research interests include ocular applications of high resolution ultrasound, glaucoma, management of ocular pain, and non-healing corneal erosions in dogs. She received her DVM from University of Florida and completed a small animal internship at North Carolina State University and a residency in comparative ophthalmology at University of Wisconsin–Madison.