Thanks for the reminder! I find it's helpful to take frequent breaks when working on these densely packed pages. For a break, leave the computer and walk around the house for a few minutes, or at the very least, stare off into the distance for a bit (so you work your eyes differently).
My other strategy is to break things up with a short transcription or two.
I recently transcribed a verrrry long (4-col broadsheet with dense type and a 3-column run-on paragraph!) that I worked on over a 2-day stretch--- before I realized documents get released after 20 minutes of inactivity. However, lucky me, it ended up being mine in the end.
The never-ending paragraph gave little visual respite, and no easy stop-points. I imagined a reviewer tsk-tsking at the shovelful of typos I'm sure I made!