Eyes tire more when working w/ detail on the computer, compared to casual browsing; & I work a lot. Does this add up over time & dmge ur eyes sooner?

No. You cannot harm your eyes by using them to see. If you want to reduce fatigue, some glasses may be helpful for this.
Possibly. Constant strain on the eyes may contribute to earlier onset of myopia, also known as nearsightedness in lay terms. One study that I reviewed indicated that subjects that worked at a computer terminal all day for 2 years, but not controls, developed myopic change at a statistically significant level.