A while back I had a very popular set of articles on eye contact in martial arts. You can find them here and here. Several of my readers gave points of view that differed somewhat. I think what is happening here is we are talking about part of the same phenomenon from different points of view (pun intended).
My contention is that you want to point your field of vision at the centerline of the opponent and keep it there, unshifting. My commentators bring up the point that peripheral vision works better and that we process better unconsciously when we are de-focussed instead of locked on a focal point.
We're talking about the same elephant here. You want to do both. you want to direct your field of vision on their centerline (perhaps nasion or suprasternal notch) and you also want to defocus into the "1000 yard stare" or " far mountain gaze" or "dead eyes" (whatever you want to call it).
Keeping your focal point fixed has a lot of advantages - see here and here, for instance, and here for the money article on the topic (it turns out that whenever you change your focal point you lose visual processing...)
Cool information, for those who want to take advantage of it - you just have to figure out how to work this into your training routine. It will make a huge difference, I promise.
You can find a set of great articles on eye control in martial arts here.