Lacrimal drainage system irrigation. A, Complete canalicular obstruction. The cannula is advanced with difficulty, and irrigation fluid refluxes from the same canaliculus. B, Complete common canalicular obstruction. A “soft stop” is encountered at the level of the common canaliculus, and irrigated fluid refluxes through the opposite punctum and sometimes partially from the same canaliculus as well.C, Complete nasolacrimal duct obstruction (NLDO). The cannula is easily advanced to the medial wall of the lacrimal sac, then a “hard stop” is felt, and irrigation fluid refluxes through the opposite punctum. Often, the refluxed fluid contains mucus and/or pus. With a tight valve of Rosenmüller, lacrimal sac distension without reflux of irrigation fluid may occur. D, Partial NLDO. The cannula is easily placed, and irrigation fluid passes into the nose as well as refluxing through the opposite punctum. E, Patent lacrimal drainage system. The cannula is placed with ease, and most of the irrigation fluid passes into the nose.