I'm "only" 66 but had an incident with my right eye this past fall that got me close to thinking about this very topic. My wife is disabled and I am the chief cook and bottle washer, pilot and mechanic. While dealing with the vision issue I had decided that if my right eye was lost I'd hang up the keys - not a second thought. Too much at stake. Too many poor drivers out there to contend with now than ever before. I think we all know when the time comes it just that some of us will not admit it. As it turned out my eye is fine and I will continue to drive until I reach that "time" myself.