Well I'm a different guy, but sincerely curious HOW.
Not saying you're blowing smoke – I believe you.
The reason this happens is due to a magnifying glass effect by the lenses, focusing the intense sunlight to a point, burning elements in the screen.
I can't imagine a way for this to happen wearing them. The angles don't work.
I don't remember when they were exposed in a manner to cause this damage, but I don't remember a lot of what was going on around me when flying, my attention is usually focused on something.
It could have an entirely different explanation.