I have no doubt that a couple of weeks ago, in the weakened state in which he was left after putting off death for a while, 18-year old Paddy cat had gone blind. The evidence was convincing - he kept bumping into things, and he had difficulty finding his food dish. The vet couldn't make up his mind: "it's hard with cats."
A steroid injection, a daily kidney pill, and some (apparently very tasty) paste in his food and he is now much restored and enjoying a healthy appetite.
And he can see again. His sight is back - or at least some of it. He can follow my movements. He looks out of the window. He avoids obstacles and can find his food. What more does an elderly cat need?