Joe O’Connor, 62, who lives near Worcester, Mass., was diagnosed with Parkinson’s disease six years ago. Exercise is one of the only things that slows the progress of the chronic disease, so he works out avidly — often in a virtual reality world. He dances. He plays tennis. He enjoys games that help him work on his short-term memory and hand-eye coordination. “VR has been a very big help with Parkinson’s, both in slowing the progression and in helping me calm down,” O’Connor says.