Mr. Sandman

Plot:

Shortly after each-other, people are attacked by a revolting fly Wesen, which causes blindness by licking, thus introducing river blindness-type parasitic worms. Nick is affected himself. Monroe and Rosalee work out they only have a few hours to prevent permanent blinding by capturing the Wesen in feral form, scooping up an eye and mixing it in a concoction. So they must find it even faster, using heirloom Grimm record clues.