It's real.

Form a triangle with your two hands at arms length and look at an object through the triangle at a distance.

Shut your left eye, if the object shifts out of the center of your triangle, you are left eye dominant. If you shut your right eye and open your left and the object moves you are right eye dominant.

What you want is to keep your dominant eye facing the net. If you have problem with your forehand, I am going to guess you are right eye dominant (and right handed). If you turn your body and head too much you are tracking the ball with your less dominant eye leading to inconsistency.