Use irons every time I shoot my muzzle loaders, or the Sharps, which is more often than the modern stuff, now a days.
Turned 70 last spring and have worn glasses since I needed them to see gophers at 35 yards, back when I was 42.
The open sights are fuzzy, but I still seem to win at both more than not, with only a moderately fuzzy front sight.
The back sight is well, nasty fuzzy.
Except - wide V and bead front sight works the best. The ball hits the centre of the fuzzy bead.