Feline Anisocoria (unequal pupil sizes)
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
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
Anterior uveitis (inflammation of a portion of the eye)
Glaucoma (increased pressure in the eye)
Iris muscle abnormalities
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 eyelid opening
A change in eye color or clarity
Diagnostic Tests for Anisocoria (unequal pupil sizes) in Cats
Complete eye examination
Thorough physical examination
Complete blood count (CBC)
Chest X-rays if trauma is suspected
Tonometry to measure intraocular eye pressure
Ultrasound of the eye and tissues behind the eye
Cerebrospinal fluid tap (CSF)
Electroretinography (ERG) to evaluate retinal function
Visual evoked potential (VEP) to evaluate optic nerve and brain function
Computed tomography (CT) scan or magnetic resonance imaging (MRI)
Treatment of Anisocoria (unequal pupil sizes) in Cats
It is difficult to treat patients with anisocoria symptomatically, as there can be multiple underlying causes that are treated in very specific ways. Your veterinarian might 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.
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.