I had that happen to a cat, who eventually went blind... the vet said it was likely a form of feline diabetes that came on in his later years...

He survived a good year or two blind... even started going out and sitting under the cedar tree a few feet from the door for half an hour at a go or so...

Then one day he went out and didn't come back... probably went off somewhere to die, the good ol' bugger...

11 years is a pretty good age fer a cat....