My eyes are getting old - I can't shoot well with irons anymore because I can't keep the irons and the target all in focus (near sighted) with my glasses on. Or I can't keep the front and rear site in focus at the same time. Peep sights are the only ones I can shoot with any consistency. You might want to try a peep site and see if that helps.
If peeps don't do it then canting or flinching might be it - as suggested earlier. I scope or reddot/Halo most of my stuff now.