[citation][nom]jamie_1318[/nom]Ever heard of computer vision syndrome? It is only temporary but a huge number of people have it all the time. It impacts the ability to focus your eyes, and causes poor ability to adjust to bright sunlight.[/citation]
I have a story from my experience you might find interesting. About 3-4 months ago I got a 3D monitor. When I first started to use it, my eyes would feel a little strained at times, almost always as result of a particular game I chose to play as my 1st run through, Lora Croft: Underworld. The straining was sometimes images would appear as though it was at your nose in depth. I eventually learned to adjust conversion and the problem stopped.
Now to the interesting part. After gaming with it for a month, and not playing normal games without the glasses, I went to play a game I was already playing in 3D, but in normal 2D (Gothic III). The interesting thing was, my eyes felt strained to play the game in 2D. My mind was used to playing the game in 3D, so it would try to refocus like I normally do with 3D and in the real world, but the game was in 2D, so it would have to refocus again.
This leads me to believe one of the reasons people may feel eye strain is that you are trained to use a 2D screen, and just need to readjust, which takes a little bit.
The only times I might feel eye strain now, is if I go to 2D, or if a game tries to display things at a depth too close to your face. I have also experienced it when experimenting with different Hz, but that's not a hardware issue.