Hello:
In addition to making sure that even the hooded post is fully blackened to prevent any reflections and trying an adjustable MERIT iris on your glasses, some have made a replacement rear sight bar with a round hole in it instead of a notch. This has been called a "peep-slider". While this is NOT N-SSA approved, it enhances the concentricity aspect of one's sight alignment/ picture. Remember, if your front sight is fuzzy, you have a vision/ glasses/aperture SIZE issue. It's best NOT to shift one's focus back and forth between the rear sight, front sight and target. Let rear and target be slightly out of focus and concentrate on the front sight and a small, consistently maintained gap between the bottom of the bull and the top of the front post. Don't look closely at your sight picture for more than 5 -6 seconds or your dropping oxygen level will increase blurring. More than 6 seconds of concentrated focus on the front sight will actually "burn" the contrasting image of the bull into your rear eye receptors so that you see it in one place while the rifle has moved! This can be observed by staring at a light bulb and closing your eyes. Keep your eyes closed, turn aside and you can still "see" its after-image. Be sure to blink your eyes before aiming to recoat your eyes with the same amount of moisture. That BLINKING thing is SIGNIFICANT.
Regards