Those look like Eskimo bone glasses, made to cut down on glare from the snow. http://upload.wikimedia.org/wikipedia/commons/c/cb/Inuit_Goggles.jpg http://uploa

Those look like Eskimo bone glasses, made to cut down on glare from the snow. http://upload.wikimedia.org/wikipedia/commons/c/cb/Inuit_Goggles.jpg http://upload.wikimedia.org/wikipedia/commons/c/cb/Inuit_Gog... Note that if the slit is narrow enough, it will still focus light thought the pinhole effect (also giving you polarized light (if the material is electrically conductive)).