For starters, I lack the appropriate knowledge to make such a thing. I just thought of the idea and figured someone out there would have the interest and ability to do it.
So here goes,
I know raspberry pi is going to have a camera module released at some point. So what if someone could program the camera to detect your eye movements, since there is already is facial recognition.
I think connecting raspberry pi to the computer/laptop should be wireless via bluetooth (they have bluetooth mice these days, right?). Or it connects to the computer/laptop via USB (some how, maybe via GPIO). And of course someone would have to write a driver for this part.
Also someone will have to design a case where the pi + camera can mount on the monitor. Or I believe some tape should suffice.
So to control the mouse, you will have to just look. I imagine winking to click. Left wink is left click, right wink is right click. If you cant wink, then your outta luck. Just kidding, if you cant wink then some sort of keyboard short cut will have to be assigned.
At the end of the day, I could see the mouse being somewhat imprecise but if it falls into the right hands or the technology of eye tracking develops, this could be a really awesome project.