One of my bettas started to lose his sight a bit when he was about 2 1/2, but I'm not sure how old he was when I brought him. I had to help him find food by keeping my finger over it. He couldn't see the pellet very well so he would miss a few times. XD
I'm gald your fish is doing well. It is a bit annoying helping a weak sighted fish eat. I don't know what I would have done if my fish needed more than glasses. >.>
even if he IS blind, there's nothing to worry about. having a blind betta is just like having a betta that can see. only difference is, you may have to train him to eat from a certain spot, and be a bit more careful with the decor you put in there.