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Anisocoria in Dogs

By: Dr. Bari Spielman

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Anisocoria is an inequality of pupil size, when one pupil is dilated and the other is constricted. The cause of anisocoria varies. Nervous system abnormalities, as well as infection, inflammation, cancer or trauma involving the eye can also result in anisocoria.

Nervous System Causes

  • Head trauma
  • Disorders of the optic nerve, the primary nerve to the eye
  • Disorders of the oculomotor nerve, a cranial nerve that provides muscle sense and movement of the eye
  • Disease of the cerebellum, a portion of the brain
  • Disorders of the optic tract, a bundle of nerve fibers associated with the eye

    Ocular Causes

  • Anterior uveitis (inflammation of a portion of the eye)
  • Glaucoma (increased pressure in the eye)
  • Iris muscle abnormalities
  • Eye cancer
  • Medications that change the function of the pupil
  • Spastic pupil syndrome

    Anisocoria can be associated with multiple disease processes, and may be just the initial sign of severe or even life-threatening illness.

    What to Watch For

  • A change in pupil size
  • A change in eye position
  • A change in vision
  • A change in the shape or position of the eye opening
  • A change in eye color or clarity
  • Inflammation
  • Eye pain

    Diagnostic Tests

  • Complete eye examination
  • Thorough physical examination
  • Complete blood count (CBC)
  • Biochemical profile
  • Urinalysis
  • Chest X-rays if trauma is suspected
  • Tonometry to measure intraocular eye pressure
  • Ultrasound of the eye and the tissues behind the eye
  • Cerebrospinal fluid tap (CSF)
  • Electroretinography (ERG) to evaluate retina function
  • Visual evoked potential (VEP) to evaluate optic nerve and brain function
  • Computed tomography scan (CT) or magnetic resonance imaging (MRI)


    It is difficult to treat dogs with anisocoria symptomatically, as there can be multiple underlying causes that are treated in very specific ways. Your veterinarian may recommend several treatments while results regarding an underlying disorder are pending.

  • No treatment may be needed in disorders such as iris atrophy or hypoplasia, in which the iris is underdeveloped or decreased in size.

  • Antibiotics and/or anti-inflammatory drugs may be recommended for certain bacterial or inflammatory disorders.

    Home Care

  • Administer any prescribed medication as directed by your veterinarian.

  • If your pet is not improving, and/or there is development of additional clinical signs, contact your veterinarian.

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