In my materials class (I'm a mechanical engineering major), we just got a guest lecture from a forensics engineer. A retired AF LtCol, he now runs his own consulting business and does all sorts of real-world engineering analysis.
One interesting case involved a KB on Kimber. The shooter was using reloads, and a round fired out-of-chamber. A piece of brass which doctor's couldn't find took out his right eye.
In the hospital, he kept telling the doctor, "I wish I'd been wearing safety glasses." The doctor told him safety glasses wouldn't have helped. So the guy thought, "If that's the case, then I'm suing Kimber."
So this retired LtCol was hired to determine if safety glasses would have helped. Estimating the speed of the piece of brass and its size, they were able to determine its kinetic energy (KE). To simulate the situation, the bought a pellet rifle which fired at 1,000 fps and used a hard-tipped pellet.
They bought over twenty pairs of safety glasses - from cheapo Walmart to top of the line from Cabela's - and fired the pellet rifle at them from 3-4 feet. The pellet had six times the KE of the piece of brass. The fired one round into each lens of all the glasses.
And none of the pellets penetrated the glasses.
So, wear 'em. They work. And don't shoot bad reloads.