Fig. 26. Deep sclerectomy with viscocanalostomy: development of the superficial scleral flap. Flap development with NPFS is decidedly more complicated than trabeculectomy. It is inherently more difficult to make two flaps from 1 mm of sclera than one flap. The superficial scleral flap should be approximately 300 microns in thickness, 5 by 5 mm and parabolic in shape to aid in eventual closure. The most common mistake is making the flap too thin with dissolution as the limbus is approached. The flap should look like C, as the limbus is approached. Various free-hand techniques may be used to dissect the flap including a razor blade (A), diamond blade (B), or a lollipop blade (C) made by Greishaber for dissecting a uniform flap.