10% of the people are born lefties.
Anyone can change their hand dominance, simply remover or cripple the dominant hand and soon you will be using the other hand with ease.
Of course, this doesn't happen often.
Same thing with eyesight. Unfortunately, it is pretty common for one eye to be weaker, and this is totally unrelated to which eye the brain originally chooses to be dominant.
The eye with the best vision will soon become dominant, just like someone with a perminantly injured arm, the other arm will soon become dominant.
However, as eyes work in conjunction, it is harder to realize that one eye is worse than the other. And if vision is corrected, it is corrected to 20/20 in both eyes, so if cross-dominance has occured, there is no reason for the eyes to change.
My right eye is weaker than my left eye. When I was growing up my right eye vision deteriorated quicker, so by the time for the yearly eye exam, my right eye was worse off than my left.
Because of that, my eye dominance would sometimes change, especially later in life when I went 3-4 years after college with the same eye perscription, just ordering contact lenses on-line at a discount place, when i though my eyes had finally stablized, but they hadn't.
Anyways, because of this, my eye dominance is very weak. If I shoot with two eyes open and unobstructed, I see double. Closing the left eye is easiest, however, what is best is to put some sort of blinder on (a little banana-sticker on the left shooting glass lense, positioned to line up with the eye) as it perserves peripheral vision.
Of couse, we also recently had a no knock warrant served on a home on the say-so of an informant, where the home-owner returned fire until the police properly identified themselves.
Also, we had a Hmong (ethnic group from vietnam/laos who allied with USA during that war) undercover offcier get in an altercation, call for backup, backup arrived and opened fire on the officer.