[BamaFan121s]

Well, not a Yorkie, but I had a Peke that went blind gradually over time...old age, bless her.
As someone mentioned, one thing important is to not make any major changes with how things are arranged in your house. Don't allow for furniture or large objects to be out of place. Renee became very dependant on vocalization in some situations, like coming in from outside--she learned to follow our voice when she was in places that she wasn't extremely familiar with. Start doing that with her now. Every once in a while you could tell that she was kind of 'lost' in where she was and would just stand still and kind of 'stare' around, but we could say something to her and she'd immediately figure it out and get going again.
Luckily, she was able to make the adjustments as she needed gradually rather than complete vision loss all at once. And really, it was harder on us than on her. She never acted like it bothered her.