Trying to figure out what triggers allow a single eye to define what "in focus" means. Seems sharpness has something to do with it, since pictures that are blurry confuse my eye. However if that is true, then i've gotta figure out how to translate that into simple triggers.
So far i was thinking that if certain qualities bleed into each other in areas, the eye will attempt to adjust. However there are plenty of objects with slowly changing appearance and that doesnt make the eye want to refocus. It might be a question of how fine the bleeding needs to be to trigger a refocus. You could probably describe where and how much a change occurs on those objects that doesnt require a refocus, but if you close one eye and look past your finger, the fuzzyness surrounding your finger is almost increscribably finely mixed.
Plus, whatever system I come up with I wont have to employ for the entire eye since it seems impossible to reflexively focus on objects in your peripheral vision.