My eyes strain badly with the new iMac display - 2014

I recently bought a 2013 iMac 14.2 to replace my 2007 iMac 7.1.

I immediately noticed that my eyes were straining very badly in front of the new screen. No matter how I tweak the adjustments, I can't bear to look at the screen long enough to do any significant work.

Since I still have the old iMac in the same room, I can easily compare by just switching desks. With the old one, no problem. The moment I sit in front of the new screen, my eyes start aching and watering. It's not a question of contrast, brightness, or any adjustable parameters that I'm aware of.

I checked on the Net, and a significant number of other people report the same type of issues. I have not found any solution, nor any explanation.

I remember that in the days of the CRT monitors on PCs, I had to adjust the refresh rate as high as possible in order to avoid headache and eye strain. Anything 60Hz or below was unbearable.

Is there a similar issue with the LED backlighting?

Does anyone have an in-depth knowledge of the specificities of LED-backlit screens, such as wavelength, variation in light intensity/flickering/refresh rate, etc.?

There is a technical explanation and - hopefully - solution, and it's not "all in your head", "get glasses", "blink twice and stare at the opposite wall for one minute"...