[Glaucoma drainage implants]

Abstract

Introduction: The number of available glaucoma drainage implants has increased in recent years and now offers additional therapeutic opportunities in refractory glaucoma patients.

Methods: In drainage surgery two different functional principles are practised. The most commonly used implants (Ahmed, Krupin, Schocket, Molteno, Baerveldt) drain ocular fluid via a silicone tube into an episcleral reservoir. Multiple studies have compared the operative results of tubes, which differ in insertion, valve, material and surface characterstics. In analogy a miniature stainless steel implant (Ex-PRESS) is implanted at the limbus into the anterior chamber and drains subconjunctivally. These implants shunt ocular fluid under a scleral flap or directly under the conjunctiva. Intrascleral systems (Seton, SLOX, Silicone tubes) drain ocular fluid from the anterior chamber into the suprachoroidal space to regulate intraocular pressure (IOP).

Results: In the literature the postoperative success rates in tube shunts range between 22 % and 100 % depending on glaucoma form and implant. Most of the studies were retrospective. Miniature stainless steel devices (Ex-PRESS) placed directly under the conjunctiva may cause erosion of the conjunctiva and hypotony. Implantation under a scleral flap decreases these complications. Compared with trabeculectomy the implantation of this shunt under a scleral flap reduces the early postoperative rate of hypotony and choroidal effusion. Microimplants of Schlemm's canal ab externo or interno should reduce the intraocular pressure by connecting the anterior chamber and Schlemm's canal. Suprachoroidal shunts are an option in patients with scarred conjunctiva. Though, complications of fibrous encapsulation and dislocation are described.

Discussion: The development of drainage implants allows the reduction or avoidance of complications which are typical of traditional glaucoma filtering surgery. However, in the absence of long-term follow-ups, the procedures with their new side effects have to be further evaluated.