Poor little lamb.
I have a ball just like that. He was a rescue, and I don't even WANT to know what the owners did to that poor snake, but he's scared of his own shadow. literally!
What I did to help him, as strange as it sounds, was to handle him MORE often, instead of less.
I got him out daily for 20-30 minutes at a time. At first, he'd just sit in a ball and not move a muscle. After a few days of that, he'd gradually poke his nose out to look at me, as long as I stayed perfectly still. A few more days, he was sticking his whole head out and looking around, and I was getting really good at playing statue.
Within 2 weeks, he was climbing and cruising around like any normal, happy ball. Right around then was when he started eating for me.
He's still VERY head shy, he doesn't want me to touch him closer than about 4" down from his head. But I still get him out 4 times a week for about 30 minutes at a time. As long as I move slowly and carefully around him he does okay. He just needed re-assurance I wasn't going to hurt him. And after the whole "leave him alone" thing didn't work, I decided to try something else.
Gale