hpst Are you certain dithering is the main problem? By the way, I just did this with my HP 25er:
"I selected Image Control and went to Video Level. There's 3 options, Auto, Limited (16 - 325) and Full (0 - 255)."
I didn't get a good sleep last night so my eyes will be strained today no matter what, but from what I can tell using Limited is an improvement over using Full.
The screen is comparatively washed out, but it's probable the monitor is doing dithering/FRC to produce Full color.
Would this help you?
Also, I've heard many find *VA panels superior to IPS for eye comfort because of the much better contrast (that's the theory). Have you tried VA panels like the one in the ViewSonic VA2452SM?
Have you tried setting your monitor video level to Limited?
About my personal case, it can be more than just eye strain. It's also how it affects the brain. Right now with this low haze HP 25er with the video setting at Limited, with the window open in an environment moderately lit by natural light, I feel as good as can be expected given the short sleep I had last night. I'm also using a black theme with a black background and white text. I've also increased the text size 140% in my browser window and I'm sitting further back from the screen.
My best monitor in terms of comfort was a high-end 19" CRT at 100 Hz that I ran at a low resolution (800 x 600, if you can believe that) and kept at a large distance from my eyes.