Outcome of ahmed valve implantation when preoperative IOP less than 21 mm Hg

Purpose: To examine the results of Ahmed glaucoma drainage device (GDD) implantation in patients with a preoperative intraocular pressure (IOP) of 20 mm Hg or less. Methods: Noncomparative retrospective case series. Results: Sixty-six surgeries in 63 patients were analyzed. Mean follow-up was 51 months. The mean drop in IOP was 3.8 mm Hg (23.3%, P<0.0001) at 12 months and 3.9 mm Hg (24.0%, P<0.0001) at final follow-up. The number of glaucoma medications used postoperatively was significantly less than preoperatively. Although the mean visual acuity was poorer postoperatively this did not reach statistical significance. Surgical success was defined as IOP ≥5 mm Hg and 20% lower than preoperatively with or without hypotensive therapy, visual acuity perception of light or better and no further glaucoma surgery. About 57.6% and 53.0% of patients were considered a success at 12 months and final follow-up, respectively. Fourteen patients (21.2%) underwent additional glaucoma surgery, 8 of which had a second Ahmed GDD inserted whereas 6 had cyclodestruction. All failures were due to inadequate IOP control or further glaucoma surgery, with no cases considered failures due to vision loss or hypotony. Perioperative complications developed in 6 cases (9.1%) whereas long-term problems related to surgery occurred in 8 cases (12.1%). Conclusions: In patients with IOPs of 20 mm Hg or less who require IOPs in the low teens and below Ahmed GDD surgery does seem to be an effective option. The success rates of surgery, however, must be balanced against the risk of complications. In addition, the relative merits of Ahmed GDD implantation versus mitomycin trabeculectomy and/or nonvalved GDDs requires further investigation.