Chronic Hypotony After Tube Shunt Surgery: A Pooled Analysis of Data From Three Randomized Clinical Trials

To describe the incidence and risk factors for chronic hypotony following tube shunt surgery.

Pooled analysis of 3 independent, multicenter randomized clinical trials.

A total of 621 patients with medically uncontrolled glaucoma, including 276 from the Ahmed Baerveldt Comparison Study, 238 from the Ahmed Versus Baerveldt Study, and 107 from the tube group of the Tube Versus Trabeculectomy Study.

Enrolled patients had been randomized to placement of either an Ahmed glaucoma valve (model FP7) or a Baerveldt glaucoma implant (model 101-350). Baseline and follow-up data were obtained on a per patient level and pooled. The associations between baseline risk factors and chronic hypotony were explored using a Cox proportional hazards regression model.

Chronic hypotony, defined as intraocular pressure (IOP) ≤ 5 mm Hg on 2 consecutive visits after 3 months, tube ligation, or implant removal for hypotony.

The cumulative probability of chronic hypotony after tube shunt surgery was 4.1% (95% CI = 2.6%-6.1%) at 5 years. Reduction in visual acuity (VA) from baseline was observed in 15 patients (71%) at the time of hypotony diagnosis. Significant predictors of chronic hypotony in multivariable analysis included randomized treatment (for Baerveldt glaucoma implant; HR = 5.12; 95% CI = 1.51-17.43; P = .009), uveitic glaucoma (HR = 3.75; 95% CI = 1.26-11.15; P = .017), and preoperative VA (per logMAR unit increase; HR = 1.55; 95% CI = 1.04-2.32; P = .031).

Chronic hypotony is an uncommon complication of tube shunt surgery that usually produces a reduction in VA. Baseline factors associated with this complication are Baerveldt implantation, uveitic glaucoma, and poor VA. This study analyzes the largest prospectively collected dataset to date on tube shunt surgery.