Calfed is right. I tried progressive lenses - fell over my own feet going downstairs (when you view strongly off-axis) and for shooting they are totally impractical (sight picture varies with the smallest head movements). You must have glasses with correction optimized for the distance to the foresight. Anything else is a false economy, and as a result a waste of money on ammo that would be better spent on getting the correct lenses!
Patrick