Manu Kumar had a bad case of repetitive strain injury from too much typing a few years ago that made clicking his computer mouse a painful chore. So he thought: why not eliminate the mouse entirely? Kumar, a Ph.D. candidate at Stanford University's computer-science department, looked at ways of making a device that could track eye movements and move the cursor on the computer screen accordingly. The problem with previous attempts to make eye-activated mice was that the cursor tends to zip around the screen with each spurious movement of the pupil. "A person's eyes are never really stable," he says. He wrote computer software that ignored the eyes' lesser movements and followed the overall direction of a person's gaze. His program, EyePoint, has an error rate of about 15 percent, compared with 5 percent for a standard mouse. Kumar hopes to commercialize the software, but he wants to finish his thesis first.