Although we have two eyes for depth perception and for spare parts, there is a natural tendency for one eye (the master eye) to take precedence over the other,
regardless of the relative visual acuity of each eye. It is a fortunate condition when the eye on the side of the shoulder where one is comfortable mounting a gun is also the dominant eye.
To test for eye dominance:
Pick out a small object several feet away.
With both eyes open, center your right index finger vertically over the object.
Close your right eye.
If your finger appears to jump to the right, you are right eye dominant.
Then open your right eye and close your left eye.
If your finger remains in position in front of the object, you have confirmed your right eye dominance.
Alternatively, if in the above test, upon closing your right eye your finger remains in position covering the object, you are left eye dominant.
If you close your left eye instead and your finger appears to jump to the left you have confirmed your left eye dominance.
Eye dominance problems can be treated with
1. A severely-cast, crossover stock to bring the dominant eye in line with the gun's line of sight,
2. A patch over the dominant eye, or just a small piece of frosty Scotch tape on shooting glasses intercepting the dominant eye's line of sight,
3. Fully or partially closing the dominant eye, or 4. Learning to shoot from the dominant-eye shoulder.
While less convenient, methods that retain the use of both eyes better preserve the ability to perceive depth in three-dimensional space, a great benefit in wingshooting.