There are very few, if any injuries documented, involving conkers, unless it's accidentally eating them in mistake for sweet chestnuts*. However, my great grandmother lost an eye playing with those toy pistol caps - they're still around though! Mind you, it was possibly the century before last when they were first available.

*The way to tell, sweet chestnuts have a point on them, horse chestnuts don't. The skins are completely different too, with sweet chestnuts looking almost hairy. These in turn are not to be confused with Plane fruit, which have stalks and no nuts.

LTS