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Ask Dr. Michael Salkin Your Own Question
Dr. Michael Salkin
Dr. Michael Salkin, Veterinarian
Category: Cat Veterinary
Satisfied Customers: 30324
Experience:  University of California at Davis graduate veterinarian with 45 years of experience.
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I just noticed my 10 yrs. old Siamese woke up from his nap &

Customer Question

I just noticed my 10 yrs. old Siamese woke up from his nap & his pupils are different sizes. What could cause that?
Submitted: 11 months ago.
Category: Cat Veterinary
Expert:  Dr. Michael Salkin replied 11 months ago.

You're speaking with Dr. Michael Salkin. Welcome to JustAnswer. I'm currently typing up my reply. Please be patient. This may take a few minutes.

Expert:  Dr. Michael Salkin replied 11 months ago.

Jeanie, this is called anisocoria and it has quite a few possible etiologies. The two most common causes are the leukemia (FeLV) virus and the spastic pupil syndrome (most likely in Max) - a condition unique to cats in which owners report anisocoria, which may sometimes be transient and independent of ambient light levels. Clinically, cats with this syndrome appear to be healthy, are visual, and have no ocular abnormalities beside unusual behavior of the pupils. Unfortunately, most affected cats test positive for FeLV at the initial presentation but not all which confounds the diagnosis.

Anisocoria also results from primary iridal (iris) disease - an example of an inflammatory process causing miosis (an abnormally small pupil); and primary neurologic disorders involving cranial nerve III and Horner's syndrome. Retinal disease - hemorrhage and/or detachment needs to be considered as well. If the retina isn’t perceiving light or telling the brain that light has been perceived, the pupil will become mydriatic – larger than usual. Retinal disease is relatively common in hypertensive cats and so blood pressure assessment is important in these cats.

The initial database should involve testing for FeLV and a complete ophthalmic examination including menace response, dazzle, palpebral, pupillary light, and vestibulo-ocular reflexes. Fluoroscein staining of the cornea should be performed looking for corneal trauma and intraocular pressure should be measured (the elevated pressure of glaucoma will enlarge the pupil (mydriasis) and the lowered pressures of uveitis will make the pupil miotic).

Much of the above is beyond the capability of many generalist vets so Max's vet may recommend referral to a board certified veterinary ophthalmologist. Please see here: www.acvo.org

Please respond with further questions or concerns if you wish.

Expert:  Dr. Michael Salkin replied 11 months ago.
Hi Jeanie,
I'm just following up on our conversation about Max. How is everything going?
Dr. Michael Salkin