Erud's comment is not valid. That does explain why he is always walking into stuff.
I started out cutting pieces from a milk jug and moving them around. You want the light to get through to prevent strain or having your sighting eye over compensate.
FTFY. Erik is generally bumping into things, and people, but sometimes I think he does it on purpose!

In my experience, I have had the same issue, though I need to take Erik's advice and get some shooting glasses and set them up appropriately (expensive as they are). The eyes need to be protected. Until that time, I usually just bend the left side of the brim of my hat down and that obscures my line of sight enough. I am, however RE/RH.