Basically? It's still hard. Identifying eyes is fairly easy, of course. Identifying open, approximately centered eyes is the easiest version of this and it's w

Basically? It's still hard. Identifying eyes is fairly easy, of course. Identifying open, approximately centered eyes is the easiest version of this and it's what we want. Basic eye-tracking efforts say something like "which of these equidistant squares did your line of vision intercept?" That's still enough to produce some cool things like "look at the red box to click it", but it's not a real-world solution. But the problem is identifying small changes and cross-referencing them with the state of the world to identify what's actually being viewed. The difference between someone looking at a sticker on a window and looking out that window is big, but the evidence available to distinguish them is tiny. Other 'natural' movements can also spell doom for eye-tracking: turning your head without moving your eyes sweeps your vision, while turning your eyes saccades it and only values the endpoints. And turning your head and body while keeping focused on a single point feels simple, but identifying it means tracking three different axes of rotation as they interact!