Cat Pupil Difference

[Splat]

My cat who is about 10 years old started having one pupil dilated much more than the other this afternoon. I noticed it early, but was unsure because she was kind of in the dark. Later, she was in direct light and it is a very noticable difference. I'm wondering what could be causing this? Her left pupil is much larger than her right, and stays that way regardless of how well lit it is or not. Help!

[Ghilly]

Horner's Syndrome (one pupil being noticeably larger than the other) is a symptom of something else rather than a problem unto itself.  It can be caused by head trauma or it can be caused by a mass pressing on the optic nerve.  

Even if you have an idea of what might have happened to your cat to cause this, you need to make an appointment with your vet to have her checked out.  For her to present with Horner's Syndrome, if it IS due to a head trauma and not a mass pressing on the optic nerve, it had to be a pretty severe trauma to cause it, so you need to have her checked out for that.  And, of course, if it's caused by a mass pressing on or some other type of irritation of the optic nerve, you need to get that checked out as well and find out what's up.  

Please post back after you've been to the vet and let everyone know what the vet says.

Ghilly

[marissposa]

any chance of head trauma?