Stateside here, our rule is that the closest thing to your eyes excluding prescription eyewear MUST be an ANSI Z87.1 rated full-seal goggle with a strap, at least for airsoft. Paintball requires unmodified premanufactured paintball masks with no exceptions.
With the airsoft skirmishing, we've generally been told that we can wear non-regulation headgear, eyewear and masks as long as we've got compliant eye protection beneath.
But then, airsoft pellets aren't as dangerous as paintballs.