With very cautious optimism, I announce that Billy's sight returned. About a week ago. As suddenly and inexplicably as it left. And we're thrilled. Although he had made tremendous strides on his own (and with training) as a blind boy, we were naturally always concerned about him and kept a close eye. And I got really concerned when his babysitters quit - after I'd given them such good press. But then I noticed that he was finding things more quickly, running more, chasing things with more accuracy, etc. And then I watched him run right at a tree full speed, knowing that there would not be a happy ending to the stunt, I was stunned to see him never break stride and run halfway up the tree. Eureka! He could see! That's why his babysitters quit; he didn't need them. His eyes don't look completely back to normal but I can't find one sight issue that holds him back. Since both of these events were without explanation, we'll hope for the best and keep an eye on him.
Billy and his babysitters and I would like to thank everyone for their kind wishes and moral support. As you can see here, he's keeping an eye on a squirrel so he's doing fine. If the situation changes, his babysitters and I will retrain him. In the meantime, we'll remain cautiously optimistic.