http://www.pickelhaubes.com/forum/viewtopic.php?t=4290
These spectacles, specifically designed to be worn with the gas mask, were issued for front-line use to soldiers requiring eyeglasses. Since the metal arms on the regular Dienstbrille (service glasses) prevented the mask from fitting tightly against the face, the Maskenbrille had short double arms onto which adjustable cotton tapes were sewn. These tapes were looped around the ears and didn't interfere with the mask's fit. These were apparently the only eyeglasses allowed to be worn in the front lines.
