pupil

one of my dogs eye is dilated and the other is not.  what could this mean?

[Aleda M Cheng, D.V.M., C.V.A]

The problem of unequal pupil sizes in your dog  is called Anisocoria.

There are many causes for Anisocoria and all of them require investigation by your veterinarian ASAP.  

The causes include diseases of the nervous system such as:
Head trauma, Optic nerve or other cranial nerve disorders, other brain disorders, and Horner Syndrome;

Disorders of the eyes themselves:
Anterior uveitis (inflammation of a portion of the eye), Glaucoma (increased pressure in the eye), Iris muscle abnormalities, and several other eye problems.

Some drugs and toxins can cause Anisocoria.  

Anisocoria can also be a symptom of several serious infectious or systemic disorders.

Diagnoses requires blood and urine tests, X-Rays, sophisticated eye tests, MRI's, CT scans, Ultrasound and more.

Treatment depends upon the cause of the problem.