The past , present , and future of surgery for suprachoroidal drainage

T argeting the suprachoroidal space with surgery is not a new idea. All ophthalmologists are aware of the effect on intraocular pressure (IOP) of a cyclodialysis cleft following trauma. A small gap between the iris root and the scleral spur can cause devastating hypotony and be difficult to manage. In 1900, Ernst Fuchs, MD,1 and Leopold Heine, MD,2 both described the inadvertent and deliberate formation of a cyclodialysis cleft, which enabled seemingly endless fluid to escape the anterior chamber. The effect was often hypotony, but this did not deter Dr. Heine from inventing the cyclodialysis spatula to refine the operation and attempt to use it as a therapeutic approach to IOP lowering.2 With no control over flow and tendency of the clefts to suddenly close, however, IOP was too unpredictable and uncontrollable, and the technique never gained popularity. In 1967, James Gills, MD, reexamined the suprachoroidal space for glaucoma surgery and devised a Teflon implant in an attempt to both control the rate of flow and prevent sudden cleft closure; however, the device was hampered by its size and the difficultly of insertion.3 The suprachoroidal space as a surgical target lost favor until the early 2000s, when the effort to improve upon the gold standard of trabeculectomy began. In 2005, Yablonski3 described a revision to trabeculectomy whereby deep sclerectomy was performed beneath a trabeculectomy flap, into which a small silicone tube was placed between the intrascleral lake and the suprachoroidal space. His retrospective series included 23 eyes, in which preoperative mean IOP of 25.4 mm Hg was reduced to 13.8 mm Hg at 324 days follow-up (mean values). Mean medication use was 3.0 drops preoperatively compared with 1.1 drops at 1 year postoperative. In keeping with the route of drainage, suprachoroidal trabeculectomy resulted in barely detectable bleb formation, suggesting that most aqueous is absorbed in the suprachoroidal space, facilitated by the high colloid osmotic pressure environment of the uveal system in preference to the higher resistance route by which subconjunctival fluid drains. Driven by evidence that, despite antimetabolite use, the subconjunctival space is prone to fibrosis and hence reduction in efficacy or late failure, emphasis began to focus on how to divert drainage to a site of perceived lower resistance and scarring. In the early 2000s, two groups investigated how existing silicone tube implants could be adapted to divert flow from the equatorial subconjunctival space to the suprachoroidal space. A Turkish group modified a Krupin implant to drain from the anterior chamber directly to the suprachoroidal space.4 This technique was closely echoed by work in Germany.5 Both attempts were made in refractory eyes with high starting pressures (more than 40 mm Hg) and showed encouraging results (postoperative IOP in the mid 10s mm Hg). One of four patients in the Turkish series developed transient self-limiting hypotony,4 and two of 31 patients in the German series required tube removal due to endothelial decompensation.5