I have to guess (not being trained in such matters) that it isn't exactly an optometrist question since it isn't (I think) about focus or optical sensitivity per se but more about the speed with which either your eyes or brain can detect changes in what you see.
Long before DLPs and their rainbows, long before widescreen TVs, Sony produced a 29 inch (4x3) TV with 100hz.
Walked into the local Sony Centre with my colleague. Immediately I can pick out the 100hz TV - the lack of flicker is immediately obvious to me. Whereas, he doesn't have a clue what I'm on about.
10 (?) years later and he now admits he can see the difference.
Visibility of CRT refresh rate flicker and rainbows is, I suspect caused by the same thing - can I call it 'fast eyes'? And, my sevsitivity is certainly getting worse (ie more sensitive) as I age. The evidence from my colleague, starting from a less sensitive point, is the same.
And the pojnts made by others here are well made. At worst, you see, and are nausated by, DLP rainbows almost immediately. At best you have no idea what the problem is. In between and you may find yourself becoming 'tired' or uneasy at watching - without being able to detect exactly why.
As for keeping your screen size small and/or staying far enough away from it to avoid lateral scanning to keep rainbows at bay - this is surely tending towards defeating the whole point of home cinema - to get (close to) a cinema-like experience in the home. Rare, I think, to go to the cinema and not have to laterally scan a wide picture. Might as well buy a TV?
Roll-on 3-chip DLPs at realistic prices Until then, it's LCD (with its greyish blacks) for me - no contest.