I think the glasses provide a place to rest the eyes in either looking at the rims or unfocusing the eyes looking at the lens.
My prescription lenses for near-sightedness seem to help me focus my eyes better at all distances, even though the visual clarity improvement only occurs at a far distance.
I like this thought because my personal experience is wearing regular perscription glasses and staring at a screen 10-14 hours every day with no eye strain or headaches. My sister loves and swears by the blue light filtering (but doesn't wear glasses otherwise)