Welcome! My name is***** am a UC Davis graduate, and currently, a Medical Director of a veterinary hospital.
I am sorry to hear about this concern for Frankie.
The frequently washing back end may be a separate concern. That can freuqently occur with problems like anal gland impaction or infection, urinary tract infection, diabetes.
The walking in circles can be suggestive of a vestibular problem (loss of equilibrium), but it is usually uncontrollable. I am suspecting maybe he walks in the circles because he is trying to get at his back end.
More concerning to me is the pupils. What you are describing is called anisocoria.
Unequal pupil size is called anisocoria:Anisocoria in Cats
This link will tell you a ton of good information including differentials for possible causes. Unfortunately, there are quite a few causes, and at Frankie's age, some of them are not easy to correct/remedy.
I would start with a vet visit as soon as possible. A vet should recommend some basic testing immediately including a blood profile and urine test.
Some viral testing might also be suggested.
I wish we could help Frankie at home, but as I am sure you already knew, these are issues that can't be treated with over the counter therapy.
I will pray for a speedy recovery.
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