Well, I know this is an old thread, but this is an important issue, although for a few people only.
I have first encountered this eye strain problem when quite a few years ago I have sold my MAG500T Trinitron CRT and bought a flat screen TFT. It was - as far as I remember - a 22" 16:9 Acer with TN panel, 6+2 bit dithering and a CCFL backlight - all the bad things. I was happy. Well... for about half an hour, when my eyes started to hurt. I have tried every setting possible, looked up some forums... in the end, after spending a few hours in front of this monitor, I got such a terrible headache and eye strain that I literally could not work for a week. I could not watch TV or sit in front of a monitor, my eyes swelled up, it was tragic.
So I did some "research", and bought an S-PVA display - a Samsung 971P. I still have it. I turned down brightness, turned up contrast, etc. Also got a lamp behind the monitor that lights the wall, and I was happy again 🙂 Later on I bought a BenQ BL2400T, which has an AMVA panel. It was somewhat harder to set up, but it was OK once again.
However, just today I got a Dell U2515H. I wanted to do some color sensitive work, get WQHD resolution, etc... And now again, my eyes are starting to melt. I look at the BenQ beside the Dell, and it's a relief. I look back, and it's starting to hurt again.
I am still evaluating this, but I strongly suspect that for me, it all comes down to contrast. And contrast is... well, more complicated than one might think. I am perfectly fine with the AMOLED screen of my Tab 8.4 S, even though it has very tiny text. I am also OK with the *VA panels, as they have about 3x the contrast of IPS panels: I can set brightness to almost zero, while turning up the contrast, so that I have really deep blacks. But on an IPS... even the blacks radiate. If I turn down the brightness up to the point where it is fine for me, the contrast becomes very low. There is just no sweet spot. If I increase the ambient light in the room, it is somewhat better, but still, IPS - and TN of course - just have way too much intrinsic light hitting my eyes, IMHO.
I would recommend to everyone that have this problem to try some sort of an *VA panel display with about 5% brightness and 50% contrast, with a lit background, and see whether it helps or not.
BTW: the U2515H was professionally calibrated.