For what it's worth, I used bifocals when I was flying with the cut-off aligning with the glare-shield when looking comfortably ahead. Now, long after I have retired, I have varifocals - they are very good except when I need to be aware of my spacial awareness, like climbing ladders, etc. I don't know whether this is relevant in the cockpit environment but I resisted wearing varifocals when I was flying so that I would not grab the wrong switch when reaching out near my peripheral vision.