I have a tortie named Koshka who's pushing 18 yrs. Over the last year, she's slowed down quite a bit which I am assuming is due to her age. She still eats and drinks well. In the last two months, I've deduced that she's either going blind or is blind. She doesn't seem to "look" at anything anymore but still manages to get around the house (both upstairs and downstairs) by memory and sound. She has no problems with going to the bathroom either. She still purrs and loves attention and shows affection but mostly just sleeps through out the day. All of these things stated, last night while I was cooking dinner, Koshka was meow-ing at the wall by the water dish. I turned her around so she was in front of the water dish and she looked up. When she looked up, I noticed that her pupils were two different sizes. Her left pupil was huge and unresponsive to shadow or light, where her right pupil seemed to be operating normally.
I know she's old, but does this sound like natural age progression or should I hurry her to a vet?