I had a strange occurrence happen with me recently. I can't explain it logically, but it is real.
I have been shooting 45 Colt bullseye using a Holosight on my single-action revolver. I started telling myself to keep both eyes open with the sight since I started using it. I do have 20/20 vision in both eyes.
Well, on one target set out of many, I started to notice my shots were walking high. I kept shooting, and all my shots started going a little high. I knew the gun was sighted and I couldn't figure out why my hold had suddenly changed.
I started examining any possible difference in my hold, when suddenly I noticed something. I had slipped back into right-eye shooting only and was closing my left.
The next target, I remembered to keep both eyes open. I started shooting, and all my shots were back in the bullseye, with none going high.
Theoretically, the sight picture doesn't change one bit, as my right eye is still the one gathering the red light from the sight. So I do not know how this outcome is possible with me, but as I said, it's real and happening. So, something about having both eyes open must change my reaction or hold on the gun, versus having only one eye open.
I will stick with both eyes open because of my experience.