A personal computer system includes a visual display, an imaging device adapted to provide eye-tracking data by imaging the face of a viewer of the visual display, and an input device for accepting eye-tracking control data and other input data. The imaging device is switchable between at least an active mode, a ready mode and an idle mode, and the switching time from the idle mode to the active mode is longer than the switching time from the ready mode to the active mode. The eye-tracking data provided in the ready mode may include eye position but not eye orientation. The system may include a dedicated input device for forcing the imaging device into active mode by directly triggering an interrupt; alternatively, the dedicated input device forces it permanently into idle mode.