Many people are, like me, unable to use a keyboard and mouse/trackpad for longer periods of time. The solution, as always, is to use your head.
Moving the Mouse Pointer
iTracker doesn’t automatically start controlling the mouse pointer when launched, even if you tell it to in the preferences. Nor will it do anything when you click the icon in the menu bar and select “Track” from the menu. It will only start working when you press the global keyboard shortcut for pausing and resuming iTracker (Cmd-Shift-T by default).
iTracker is the only Mac head mouse software I know of that actually works. It uses the web camera on your Mac to locate your face, see which way it is moving, and move the mouse pointer accordingly. Sounds weird, but it quickly becomes second nature. After adjusting speed and sensitivity you should be able to reach all corners of the screen just by turning your head.