Modern aqueous shunt implantation: future challenges.

The aqueous shunts that are currently available are based on the principles of the Molteno implant, i.e., a permanent sclerostomy, routing of aqueous to the equatorial subconjunctival space, and an end plate to prevent obstruction, and also to determine the surface area for absorption. While the Ahmed Glaucoma Valve appears to have improved the predictability of early intraocular pressure (IOP) control, the Baerveldt Glaucoma Implant has a tendency towards a lower rate of long-term excessive encapsulation. As a result of improvements in predictability, shunts are used more widely. Because of these positive factors, and ongoing concerns regarding the bleb-related problems associated with mitomycin C trabeculectomy, there is an increasing interest in the use of shunts as primary surgical management for primary glaucoma. At present, the main barrier to wider use of shunts in less-complicated glaucomas will probably be the unknown long-term effect on corneal endothelium, an issue that has not yet been properly addressed.