Arc flash is essentially a sunburn on one's eyeballs. Like a sunburn, it occurs over the course of time, one needn't be looking directly at the arc in order to get it, some time elapses between exposure and onset, and it's temporary. Arc flash does not cause blindness, but it is uncomfortable while it lasts, and too much exposure during one's life can cause cataracts to develop.
The arc light can burn one's skin as well, just like the sun.
