For shooters with two eyes of fairly equal vision, you can determine your dominant or master eye by holding your hands out in front of you at arm's length, forming an opening between your hands as shown in the photo. With both eyes open, center an object in the opening between your hands. Now, close your left eye. If you can still see the object, your right eye is dominant; if you cannot, then your left eye is dominant.
The dominant eye is important because that is the eye that your brain automatically "wants to" use when aiming a gun. Realizing which eye is dominant can be very helpful in deciding how you should practice and aim. A right-handed person with a dominant left eye may end up doing everything else right-handed, but shooting a gun left-handed.
If, like me, you find your eyes fairly equal in dominance, you should shoot with your strong hand (right for right-handed folks) and close (or at least squint) the other eye when aiming.
- Russ Chastain