I have noticed that, mine are now left of center focus, so the reader part is in focus when I am playing guitar and reading sheet music which to my left. That really helps when shooting right handed, but hampers me when shooting left handed. My vision is nearly 20/20 with an astigmatism, so I take the glasses off sometimes, when I shoot left handed. It does not affect my aim, since I use the the secondary indirect method either way.