Before you watch the video, the general idea is that there are infrared (IR) illuminators and a camera at the base of the laptop display. That is used to highlight the player’s eye, even in dark or overly bright conditions (hence the IR spectrum). The camera will determine where on the screen the player is looking at, based on the positioning of the head and eyes relative to the camera. The accuracy is about one-inch square.
In the video, the player is using Tobii as a secondary controller that is used to select the next jump target. Notice that the game’s character position and movement are not affected at all by the eye tracker.
To make this work, game developers have to revisit the code of each title, and as you can guess, how much value eye-tracking adds depends on the type of game. Also, how much work is involved will vary depending on how the game’s code was designed to begin with.