Really sorry to hear he's not getting better. Our Pit Bull George, had a tumor on his brain. We thought he had dementia and had gone mostly blind. But his eyes were fine as the vet checked. It's was the tumor that showed on xray that was the problem. He could see. Just couldn't process the visual info coming in. In the end, at 13+, it was just his time to go. Didn't want him to suffer and the vet agreed, while they could give him med's to make him comfortable, it was just a band-aid and we weren't going to prolong it just to delay him going for our sake.
If you haven't already, perhaps a second opinion.
Like children and old folks when they're cognitively on the decline, they can still realize how to get attention by making a fuss. So one can't rule that out. But unfortunately, it just may be the time for the hard choice we all hate to admit it may be time to make.
Really wish the best for you.
Bert