Fig. 34. Deep sclerectomy with viscocanalostomy: viscocanalostomy. After identifying Schlemm's canal, Healon GV (Pharmacia and Upjohn, Uppsala, Sweden) is injected carefully into its ostia. This is a very delicate maneuver. A special cannula with an outside diameter of 150 microns and inside diameter of 110 microns is inserted 1 mm into the canal. Initially, a small amount of Healon GV is injected into the canal that refluxes out. This is irrigated away, and several more applications of viscoelastic applied, gently sliding the cannula further into the canal to a maximum of 2 mm. Great care is taken to keep the cannula in the canal. Any rotation about the axis of the cannula will cause laceration of the canal. Normally, the height of the canal is 30 microns. Dilation increases the size to approximately 200 microns. However, postoperatively, the lumen of the canal gradually decreases. Both sides of the canal are filled. After removing the deep flap, the canal is filled again to prevent reflux of blood from Schlemm's canal into the intrascleral cavern.