People with hand, arm and shoulder mobility issues use headmice to control computers. A typical headmouse combines a high resolution web camera and a reflective dot on a user’s forehead.
Here’s a link to a free headmouse tool that doesn’t require extra hardware (assuming you already have a webcam on your computer). I tested it out with my laptop’s built-in webcam. After making sure my face was adequately lit, it worked quite well for me.
It’s a little cumbersome to learn how to use initially. It’s actually quite useful, once you get the hang of it. The research group responsible for the software has created several other assistive software applications on their website for download.
Here’s a link to a site that sells the more expensive devices.