One more thing that may be relevant when testing out a monitor. Most people on computers, and in general, have a tendency of staring rather than using their eyes more easily, actively, and naturally. This is partly why glasses are so prevalent. When the eye muscles tense up from repeatedly using the eyes in a tense, overly focused way, they permanently elongate and the person becomes myopic.
I notice these days it's typical for most people to wear dark sunglasses just being outside. They can't seem to tolerate light or glare very well at all. So just try to keep the eyes moving and relaxed. When testing a monitor one is more likely to want to focus too hard to look for problems and defects.
Just an update on excessive lenses use: where I am it's very dusty and I was just on my bike, and picked up quite some grit into my eyes, which obviously is irritating, so one of the reasons people may be wearing sunglasses as much as they do could have to do with keeping dust and grit out of their eyes.
One other note for keeping the eyes hydrated: every so often, you should take a moment just to close your eyes and collect your thoughts. Just 1 minute like this every hour will help a lot.