I believe the Mishnah B’rurah quotes a Shlah that one who has his eyes open during Shmoneh Esrei will not be Zoche to see the Geulah. The M”B adds on that if one is looking in a Siddur it’s fine, if I recally correctly.
From what I recall, most Poskim don’t seem to bring this concept down. So we probably have a Makom to be Meikel (and certainly a Limud Zchus) Mistimas Divreihem.