I've used that idea of putting fingers together (though I have a one handed way of doing it) to get enough focus to look for my glasses when I've had them fall off the bedside table and "out of sight" a few times in the past

And the pinhole sunglasses were one of the things I think Tomorrow's World mentioned years ago as eye trainers as they allowed you to see but also encouraged your eye muscles to work to help keep them healthy and better able to focus on things (though those of us with astigmatism need more than strong eye muscles!)

http://www.jdharris.co.uk/product_info.php?pName=pinhole-glasses