It seems to be an unavoidable problem. I've definitely told the actors the trick of looking at the sun with their eyes closed just before the take and whether it's a placebo or not, it usually helps them deal with it.
This definitely works, I originally grabbed this trick from some photographers I knew. Closing your eyes while looking at the sun essentially "stops down" the theoretical f-stop of your eye. Sounds crazy, yes, but when the eyes are closed, and a harsh source is hitting them, light still gets through, so rather than the normal black seen behind the eyelids, some light squeezes through. As a result, your eye adjusts, and what it used to think as a good "black" is now much brighter, so handling those brights becomes much more manageable.
It's the same thing (only opposite) as turning on any light in a pitch black room, the eye was adjusted to complete darkness, and essentially "opened up" in order to get some detail in the shadows. The eye is constantly adjusting to its environment, so if you get it used to the brighter scenario, it will compensate.