eye dominance
I shoot handguns from the Chapman stance (modified Weaver) and just slightly shift my head to the right to line the left eye up with the sights. Doesn't affect binocular sight or peripheral vision or any of that. It's not a big deal for most shooters.
I’ve instructed in firearms on and off at the local regional police academy since 1988 and in the ANG as a combat arms instructor for 10 years and as an LEO since 1982. It is my observation that about 20% of the population have a cross dominant master eye.
When shooting rifle, I fire from the right shoulder, close my left eye, and shoot with the right eye. Some people (10%?) can't independently close one eye or the other and leave the other eye open (often can't close the master eye) and I'm not sure what the solution is for those folks when they're shooting a long gun. Some people have a greater natural tendency toward bilateralism/ambidexterity than others, and some can fire off the weak shoulder with some ability, but most people can't do that.
I know a minority of instructors try to take a cross-dominant shooter (right handed -- left master eye, for example) and try to teach them to shoot left handed. That's worked well for some shooters and not at all for others . . .
I can't use occluded eye gunsights with my particular set of vision characteristics, and in my experience most cross-dominant shooters can't either, but I do know a few cross-dominant operators who can without significant difficulty. So, it's a little hard to come to a rule that's "carved in stone", particularly since a person's eye sight may significantly change over the course of their lifetime/shooting career.