Anisocoria is an inequality of the size of the pupil, 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 ordeal involving the eye can also result in anisocoria.

Nervous System Causes

Head trauma
Disorders of the optic nerve, the main 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 part of the brain
Disorders of the optic tract, a bundle of nerve fibers connected 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 related 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

Treatment

It is tricky to treat dogs with anisocoria symptomatically, as there can be multiple primary 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.

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)

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