Gamasutra and explained how company's pursuits enables it to "improve the experience of both able and disabled gamers."
In addition to previously documented research into sign language, Valve's Ambinder also expresses interest in "the potential of eyetrackers and the eventual ability to let gamers use their eyes as active controller inputs." With this method, you may be able to control a game completely hands-free ... without having to use your entire body as an input device. "It may be possible in the future to let the eyes act as a proxy for the mouse cursor, letting gamers transmit navigation and targeting inputs via eye movements. If you couple this approach with the use of blinks or other proxies for button presses, you may remove the need for a mouse and keyboard (or gamepad) all together," Ambinder added.
While eye tracking sounds particularly ambitious, there are many other efforts in place by designers to make a game work better for disabled gamers. Read the full Gamasutra write-up for more.