Yes...the vieable screen portion of a 24" iMac sits higher than you (or at least I) would normally adjust a 24" monitor. With bifocals it makes it even worse to have the screen sit so high.
Remedies are: 1) Lower desk - just bought a new desk to accomodate the iMac and my existing 24" monitor in a dual configuration, so that was out. 2) Buy a higher chair - my seat height is already 20.5" off the floor, which is almost the max for most chairs....and I'd want a "good" replacement chair that would cost minimum $400 and gain me maybe an inch more height - so that's out for the time being. 3) figure out a way to lower the iMac height - iMac doesn't come with VESA mounting holes...you need to buy a VESA adapter ($25), spend an hour installing it, then buy a VESA arm or stand capable of supporting a 24" monitor that weighs 25 pounds. I took choice 3.
Otherwise, I LOVE the iMac!