Maybe you don't know:"The old saying is "if you shoot with 2 eyes, you'll shoot twice as good". In my experience this is true. From a physiological standpoint, modern medicine supports this hypothesis. When you close one eye, your OPEN eye will have a sympathetic reaction. It's part of our natural nervous system. When we blink, BOTH eyes naturally blink together. When we look left or right, BOTH eyes move together. When we shift our focus from near to far, BOTH eyes with focus together. Have a friend only close 1 eye, and watch their open eye. It will react as well. The eye will slightly close, and the pupil will slightly react (usually dilate). What you CAN'T see is that the lens of the eye also reacts, and the muscles in the rear of the eye become tense.
However, if you leave your left eye open, your brain can ignore the signals from the left eye (which is the exact reason we have a "dominant eye" in the first place), and your focus can be dictated by your shooting eye.
PLUS, when you shoot with both eyes open, you have much better visual acuity. Even though your left eye won't be trained down the sights, the signal from your left eye will get processed in your brain to improve the picture of your target. Your left eye has an unobstructed view of the target, while your right eye is obstructed by the rifle and sights, or scope. Your brain will ADD the signal of the target and the range field as viewed by your left eye to complete the picture of the target, and giving you a better/wider/more complete view of the field.
ADDITIONALLY, by closing one eye, you GREATLY reduce your ability to judge distances accurately. Your brain processes the position of your eye required to focus on a given target to determine its range. Just like the adjustable objective on a rifle scope. Closing one eye takes away your ability to essentially triangulate the range, position, and speed of the target. This greatly reduces your ability to perform for action shooting and wing shooting.
For shotgunning, you need to be able to see the entire field, and need to be able to judge distances and speed of the targets, and you ALWAYS need a high visual accuity for any type of shooting. For a long day at the range, your eyes will fatigue much more quickly if you close one eye, making your shots more sloppy as the day goes along.
Bottom line, you need to learn to shoot with both eyes open."
DJ certified instructor.
The XD solution helps you to eliminate the eye cross dominance or cross firing handicap and shoot both eyes open like any other visually normal shooter