Just thought that I would post this here for the benefit of search engines. When I recently moved to a new machine but kept the same 19" Envision CRT, I noticed the same symptoms of blurry text in the center. I checked the display adapter settings, and the new system (NVidia 8500 GT) had defaulted to 60 Hz refresh rate. I set it back to the 75 Hz that my previous ATi card was using for years. Bingo! Man, what a difference. All blurriness gone, sharp as a tack.
I don't know if this will resolve issues for everyone experiencing this problem. Probably not, if the issue is truly hardware-related. But, it doesn't take long to check, and the improvement is definitely worth the time!