John is a classical pianist and he's suffering from repetitive stroke injury. As a result, he wants to minimize his computer work. Leo says that the first thing to try is a track ball. It's a different experience in navigating the screen that uses different muscles but still does the same job as a mouse. He should research ergonomics. It's not only what equipment he uses, but also how he sits, how he places his hands on the keyboard, the keyboard itself, and more.
There are also different kinds of mice including a foot mouse, a mouse he'd hold in the air, and even a facial reader that looks at where he looks on the screen and translates that into mouse movement. A touch screen laptop is another option that may even be better. Then he doesn't have to use a mouse at all. On the Apple side, an iPad Pro would be great.