Sinusotomy and deep sclerectomy.

Non-penetrating filtering surgery (NPFS) started in 1962 with the first sinusotomy performed by Kraznov. At that time, the author of this new technique believed that the outflow resistance in the majority of cases of primary open-angle glaucoma was located at the level of scleral aqueous drainage veins and not in the trabeculum. He therefore developed a safe NPFS technique, leaving in place the trabeculum and the inner wall of Schlemm's canal. Because of difficulties with the microsurgical technique and the small reduction in intraocular pressure (IOP) compared with trabeculectomy, sinusotomy was abandoned. In the last decade, with the widespread use of operating microscopes, NPFS has been the subject of renewed interest. IOP reduction with the new NPFS techniques is comparable to that obtained with trabeculectomy, with significantly lower pre- and post-operative complications. The new NPFS techniques such as deep sclerectomy, ab externo trabeculectomy and viscocanalostomy present definitively different mechanisms of filtration compared with early sinusotomy. This article will review the history of NPFS as well as describing the different new non-penetrating filtering surgeries.