Fig. 19 Probing and irrigation of the nasolacrimal system. Hydraulic pressure is used in an attempt to force fluid through the obstruction at the valve of Hasner. If this attempt is unsuccessful, the cannula is slipped down to the point of obstruction and pushed through gently but firmly. Dye is injected from the syringe, and the patency of the system is confirmed by suctioning the dye from the inferior meatus with a soft pediatric-size plastic suction catheter.