My age requires the use of tri-focal corrective lenses. Problem is, there is no way to focus while shooting. The top portion allows target focus, but the front and rear sights are badly out of focus. The mid-range portion covers the sights, but the target is blurred. The bottom is only good for the rear sight. Same problem with rifles/shotguns. My optomertist was no help at all, he must be a klintonite. Has anybody else faced this problem ? What's the recommended solution ?