"Eyeball Control" coordinates the convergence angle between eyes and their focusing (accommodation). When you look at distant objects the convergence angle approaches zero (both eyes straight ahead) and the accomodation is near minimum. (The cornea compression muscles are most relaxed.) For close-up objects the convergence angle becomes appreciable and the accommodation approaches maximum.
Brains have the equivalents of look-up tables, generated by adaptive neural networks, that provide proper coordination of these functions. (Iris control figures in too, but is not addressed in this discussion.)
When you watch a 3-D movie or use a stereo-viewer the convergence angles between your eyes vary as a function of the original distances from the objects to the camera(s) that recorded them but the distance from your eyes to the images is fixed. When your brain employs its normally coordinated look-up tables, you get focusing commands (accomodation control) that conflict with the convergence controls. This is called an accomodation convergence conflict.
In short, and this is just my opinion, you can strip some neural gears in your head by using artificial 3-D viewing schemes, including virtual reality (VR) systems. This leads to two things. You get a headache (as the gears are stripping) and ever thereafter your look-up tables become fuzzier logic systems.
As a teenager and young adult I did a lot of artificial stereo viewing,
the kind that I claim will strip some of your neural gears. When I was 26
years old, I nearly got washed out from Navy pilot training because of
marginal performance on the navy's depth perception testing. I can't
authoritatively claim an actual connection between the 3-D "experiments"
and my depth perception tests difficulties, but I have a gut
feeling that it exists.
My advice is that if you want to retain your very best depth perception (for whatever reason), then don't go to 3-D movies, don't use stereo viewers, read 3-D comics with the red-blue viewers, or use any product that displays stereoscopic depth information on a flat surface. (I would especially avoid using virtual reality 3-D systems.)
Maybe it's time that somebody actually conducts a study to see if any long term effects accrue as a result of using VR/3D devices. Subjects would be rigorously tested for their depth perception ability before, during, and periodically for weeks, months, and years afterward.