Distance doesn't matter for a fatigue perspective. Light intensity and time are big factors, though.

Focusing on a short distance for a long period of time has been associated with myopia (though I'm not sure if they've established a causal link).

I didn't really answer your question. Sorry. No I'm not aware.

Not aware. But I was once examined by an eye doctor after having been exposed to a quite intensive amount of light. He said that during eye surgery they used very powerful light. So I think the bar is quite high, in comparison to AR glasses

Photons don't care about distance.