That would depend also on what country and what state you are in....here in the US what constitutes self-defense and how much force is allowed to be used varies. States with very liberal weapons regulations like Texas you probably could blind someone in self-defense (even if permanently) and face no repercussions.
But in some states burglars have been injured while breaking into homes and they have sued the homeowner for compensation - and won! Hard to believe..... In some places you probably could be sued, and lose, if you blinded someone in self defense. But whether or not you'd face criminal charges would depend on so many variables it's impossible to say.
Mostly it's about "reasonable" force.....if someone punches you, you have the right to punch them back, but you don't have the right to then go on and kill that person. That would be unreasonable force. Someone who's going at you with a deadly weapon and you blind them with a laser, I'd think that would be very reasonable, especially if that's the only thing you had on you that could be used as a weapon.