My last Yorkie passed away at 15 years old from a brain tumor. The vet gave us prednisone too and it worked for a few weeks but then stopped working. I made the decision to put him down because in addition to being blind he had a stroke on one side and kept falling and was starting to cry/scream in fear/frustration. It's definitely not an easy decision to make. It's now a year later and I have two new Yorkie puppies but I still grieve over that decision. Some days I feel guilty for not doing it sooner when he was suffering so much. Other days I feel guilty for having him put down. I made the decision I did after speaking to a vet who told me the best way to make the decision is to look at how your dog is coping, if he seems to be uncomfortable or not. I know it's difficult, I'm sorry you're being faced with making this decision
thinking of you!