Virtual Reality (VR) headsets and it's health risks

VR hardware has been a big break this 2015. A whole bunch of companies big and small with their headsets. I have tried some of the mobile headsets from cheap gogle cardboard types in plastic and a good version of Zeiss VR one headset as well. The experience is there at varying degrees. But one thing everyone talks about is motion sickness and I had problems with strains in my eye with VR one though it has good quality optics. How safe are these headsets in the long term for the eye for prolonged users? Another thing I notice is the brightness of some content which is quite bright and moving right in front of your eyes whether it be a video game or some 3d content. This surely has impact on our eyes as well compared to a console or a pc which is not in right in front of eyes but at a distance and most times some ambient light as well. What do you guys think about this in the long run? I do enjoy some of games and content with these headsets but as am trying out things I had been wondering how this is affecting my eyes.

Motion sickness is not a problem if your graphics hardware is fast enough to run your particular application. Anything below 75 Hz makes me feel sick, and anything above that feels okay.

With respect to your eyes, I don't think there's any kind of issue if your VR experience is good. I certainly haven't noticed anything, and I've had a DK2 for about four months.

A blackened scene with small, bright objects could be compared to a disco environment with black lights and glow sticks. Have there been any studies on discos and the long term effects on the eyes? Then again, I suppose this could not be much worse than driving at night while seeing all the oncoming headlights.