Complications Common to Nonpenetrating Surgeries

Nonpenetrating glaucoma surgery encompasses techniques that involve a deep dissection to the level of Descemet’s membrane, allowing aqueous seepage. The major techniques covered by the term “nonpenetrating surgery” are deep sclerectomy with or without implant and viscocanalostomy. In large meta-analyses comparing nonpenetrating procedures to trabeculectomy, trabeculectomy resulted in lower intraocular pressures (IOP) but a higher risk of postoperative complications. Although nonpenetrating surgery is successful in lowering IOP, the amount of IOP lowering is typically not as low as can be achieved with trabeculectomy. Consequently, patient selection with regard to the target IOP is important in the decision of whether or not to perform a nonpenetrating procedure. The goal of nonpenetrating procedures is to lower IOP with fewer complications than are seen with trabeculectomy. The complications that can occur can be easily understood and predicted by an understanding of the techniques and modifications, as well as knowledge and mechanisms of the adjustments that can be used postoperatively to enhance success. After appropriate anesthetic, the techniques involve a deep dissection in the sclera to the limbus. In the case of deep sclerectomy, after the initial half-thickness flap is fashioned, a second deeper flap is created and excised. This dissection is taken to the level of Descemet’s membrane, allowing controlled flow of aqueous. A fine forceps may be used to strip the outer wall of Schlemm’s canal, further enhancing the flow. The space created by the excision can then be filled with an implant, such as collagen (AquaFlow™ Collagen Glaucoma Drainage Device; STAAR® Surgical Company, Monrovia, California) or hyaluronate (SK Gel®; Corneal Laboratories, Paris, France). For viscocanalostomy, Schlemm’s canal is identified and dilated by using viscoelastic. With deep sclerectomy, intraoperative or postoperative antimetabolites may be used to try to increase success rates by limiting the inflammatory response. Goniopuncture to the Descemet’s window is often required postoperatively (in up to 67% of cases) to enhance flow and lower IOP. The available evidence on complications of nonpenetrating glaucoma surgery is relatively sparse and may be challenging to interpret. Comparative studies between trabeculectomy and nonpenetrating surgery would seem to show fewer complications in the nonpenetrating group.