I'm glad he's doing better, but to be honest, he's very, very old, and is probably reaching the end of his lifespan. Considering that most buttons only live a couple years, you've taken great care of him, and he's had a great life.
Keep him as comfortable as you can, keep up the good work.
He's nine years old?! That's amazing. They normally live about 2-3 years.
If you still have some of the eye medicine left, I'd keep using that. You mentioned that you don't see any signs of mites, but it wouldn't hurt to put 1/4 to 1/2 a teaspoon of diatomaceous earth in his dirt batch.
I...