Ok guys I have a quad 27 inch iMac that I bought back in 2009. I have been having severe eye strain and migraines that have gotten really really bad to the point where looking at the screen for five minutes now makes me sick to my head. I've read pretty much everything on the net about what might be causing this. Most people say it's the glare on the iMac (which I don't agree with). Some say to turn the brightness down, others say to turn it up. Some people recommend having some light in the room so the light from the display is not too harsh on the eyes. Some people say to place the iMac further away. Some people say the resolution is too high. Some people say it's the LED back lighting technology, some say it's the flicker when you dim the display etc, etc. Well I've spent time thinking about it and actually looking into how the display panel is built and I think I've possibly discovered what it is. If you take a really close look at the top left corner of the 27 inch display at an angle (with glass panel off), you can see two layers, the transparent lcd surface where pixels reside (don;t know what you call it) and the actual backlight surface panel. I have three other non apple displays that I use at home of different sizes and have compared them with the 27 imac screen and have noticed that the imac has at what looks like a 1/4 inch gap between these two surfaces, while the other non apple displays have less than that. My theory is that the terrible eye strain that I have been experiencing and that many people have been mentioning in posts on the net has to do with this 1/4 inch space. The eyes need a solid surface to focus on, if there is a huge gap like the apple displays use, the eyes constantly fight to focus between the two, hence the eye strain. As the space between these two surfaces increases the worse it gets. I have been dealing with this issue for a while know. I even went to my eye doctor and everything checked out fine as he said I had 20/20 vision. He did say to spend less time on the computer. I probably spend 1 hour a day which is very little. Right now I have an apple 23 cinema display which I use with absolutely no eye strain or headaches and I can use that for hours. I am now in the process of putting the iMac up for sale on ebay. I love my iMac very much. I like looking at it, but can't look at it if you know what I mean. What I would like to do is get a good used apple 30" cinema display and pair it with a mac mini or older mac pro. What do you guys think of all of this. Comments please.