They have a system worked out: If he loses track of the ball, she says "cold, cold" if he's far from it or "hot, hot" as he gets closer. And then he finds it!
Myron is a boxer-border collie mix who has been blind since birth. I did a little googling, and it turns out he's a bit of a celebrity in Australia (and now here on the Cute!). He has his own Facebook page and Facebook group and now he even has a book called The Magic of Myron!