Same problem here. Ironically, just today I posted the follow comment to a huge apple discussions forum thread of 90 pages with nearly 1400 responses on the issue of ill effects from apple displays (https://discussions.apple.com/message/22134685#22134685):
I just returned my new 27-inch iMac because of the screen. Like people are reporting here, it immediately gave me serious eye strain, tightness in the eyes, foggy/light-headedness, nausea and mild headache. After a few days it got a little better, but never abated completely. It seemed like there was a very faint shimmer to the monitor -- not a flicker, but a very subtle shimmering. I had a very hard time focusing on the screen -- it felt like my eyes kept jumping around. I could barely look at the screen when scrolling. My eyes would not refocus on text when scrolling stopped. I turned down brightness, I installed f.lux to adjust the color temperature, I installed bias lighting. While it helped somewhat, the unpleasant effects never fully abated. Plus I found myself staring at a very dim yellow screen. Seems to defeat the purpose of having a $2,000 iMac.
I have absolutely no problems with other LCD monitors or screens. I have been staring at a 17-in iMac (2006 rev 4,1) for the last 7 years for hours on end 6-7 days a week, with no ill effects. I use an HP 22-inch at the office, have a 2008 13" MacBook that I use regularly, and an iPad 2 that I use all the time. No problems with any of them.
I am now back to using my 2006 iMac running OS Tiger, which is very long in the tooth. I was so looking forward to the new iMac. I will likely buy a mini when it is refreshed, hopefully within the next couple months, and start searching for a monitor that will not make me sick. I have seen some suggestions in this thread, but if anyone can point me to monitors (models, or specific characteristics -- type of backlighting, coatings, etc.) that might work for me, I would be grateful.
I wish I knew what was causing this so I would know what to avoid in a new monitor. It could be any number of things in combination or alone: the LED backlighting (the brightness, reported at 407 cd/m2, or the high blue color spectrum), the IPS, the glossy screen, the front glass being laminated to the LCD, the particular anti-glare coating that is used, the contrast ratio (reported as 904:1), the PPI (reported as 108.79). Ever since I got the new iMac and experienced the problems I have been scouring the internet for answers. I can't say I am much the wiser.
Didn't realize it was you who posted there...I just left a follow-up as well. Thanks for sharing, glad I'm not just randomly having severe issues.
Took back the iMac yesterday unfortunately. My eyes still physically hurt and I can work decently on my Air or Dell monitors but having lingering effects. I had no issues at all before I bought this machine
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Did you experience this problem out of the box?
I did, noticed it the moment I fired up the machine. Then things got worse the more I tried to use it.
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I would say it's definitely the glossy screen on the iMac. I know they are supposed to have reduced that somewhat, but having looked at it in store I thought it was still too reflective for my taste. I had symptoms like you describe when I first got my MacBook Pro. At least with that, I can tilt the screen so it doesn't pick up as much reflection. Really wish they would make a matte screen version of the iMac.
What is strange is that I didn't have the slightest issue on my 2012 or 2011 iMacs which were glossy as well. I also have my office setup so glare either from overhead lights or windows is a non-issue so I would hope that isn't the main problem, but I'm sure it's not helping.