I just came across an old article on computer glasses. The author, Jim Seymour (PC Magazine, Oct 24, 1995) claims that what he called the "lag of accommodation" means that the eye focuses a bit further back than the physical distance to the screen, at the "resting point of accommodation". This differs for individual people, and is the correct focus plane distance for computer glasses. The article says that this applies to either CRT or LCD screens.
Hope this is of some interest and/or help.