Anisocoria (unequal pupil sizes) in Cats

Cats

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

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 eyelid opening

A change in eye color or clarity

Inflammation

Eye pain

Diagnostic Tests for Anisocoria (unequal pupil sizes) in Cats

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 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.

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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  The right eye of this cat has Horner's syndrome. The four classic signs are a small pupil, a narrowed opening to the outer eyelids, protrusion of the third eyelid, and sinking of the eye into the socket. Photo provided courtesy of Dr. Rhea Morgan