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Dr. Michael Salkin
Dr. Michael Salkin, Veterinarian
Category: Cat Veterinary
Satisfied Customers: 28538
Experience:  University of California at Davis graduate veterinarian with 45 years of experience.
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My two-year-old cat suddenly developed a left big pupil he

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My two-year-old cat suddenly developed a left big pupil he has no other neurological symptoms he's eating and drinking and cleaning himself
Customer: replied 11 days ago.
No trauma prior infections.

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.

Tracy, this is called anisocoria (unequal pupil size) and it has quite a few possible etiologies. The two most common causes are the leukemia (FeLV) virus and the spastic pupil syndrome - 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, many 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 - as you've reported. Retinal disease is relatively common in hypertensive cats and so blood pressure assessment is important in these cats. A vascular accident (stroke) is very unlikely at his age.

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 your vet may recommend referral to a board certified veterinary ophthalmologist. Please see here:

Please respond with further questions or concerns if you wish.

Customer: replied 11 days ago.
Thank you so much for the response I will not emergently take him into the vet today I will wait till Monday and get the appropriate test. Is there anything else I should be doing right now

No, there's nothing to be done as long as the eye is "quiet" - not "red" (inflamed). I agree with you. An ER visit isn't needed at this time. You're quite welcome. I can't set a follow-up in this venue so please return to our conversation - even after rating - with an update at your convenience. You can bookmark this page for ease of return.

Dr. Michael Salkin and other Cat Veterinary Specialists are ready to help you

Thank you for your kind accept. I appreciate it.

Hi Tracy,

I'm just following up on our conversation about Tracy L Cheshire. How is everything going?

Dr. Michael Salkin