Study Reports Chronic Hypotony Uncommon After Tube Shunt Surgery

Many factors, such as race, sex, prior laser treatment or trabeculectomy, lens status, neovascular glaucoma, number of glaucoma medications and Ahmed (rather than Baerveldt) glaucoma valve implantation, were not significantly associated with the risk of chronic hypotony in patients who underwent tube shunt surgery in clinical trial. Photo: Justin Schweitzer, OD. Click image to enlarge. Surgical trends in glaucoma have shifted in the last decade. Trabeculectomy and tube shunt surgery, both mainstays for intraocular pressure (IOP) control in previous eras, have been giving way to early intervention with low-risk, minimally invasive alternatives. However, trabs and tubes do still have a role for advanced cases that cannot otherwise achieve IOP control.In a recent review of tube shunt clinical trials, researchers from various United States academic institutions observed the incidence and risk factors for chronic hypotony in patients who underwent this procedure. The investigative team analyzed the Ahmed Baerveldt Comparison Study, the Ahmed Versus Baerveldt Study and the Tube Versus Trabeculectomy Study. A total of 621 subjects from these studies with medically uncontrolled glaucoma were chosen for the review.“Although most studies define ocular hypotony as IOP below a specified level, definitions of chronic hypotony vary,” said the authors in their paper. “For example, some studies use IOP < 5mm Hg as a criterion for chronic hypotony, while others use an IOP threshold of 6mm Hg. However, a numerical definition of hypotony does not address the fact that some patients tolerate low IOP without structural changes and with preservation of good vision.”For their review, researchers defined chronic hypotony as IOP ≤5mm Hg measured at two consecutive visits after three-month follow-up. Additionally, if tube ligation or implant removal for hypotony was recorded in a subject’s follow-up data, then they were considered as a reported case.At five years, researchers examined the probability of chronic hypotony after tube shunt surgery, the reduction in visual acuity and the significant factors associated with this complication. They found 21 patients who presented with hypotony, resulting in a probability of 4.1% at year five. In 15 of those cases, visual acuity was reduced at diagnosis of hypotony. After calculating hazard ratios for associated factors, use of a Baerveldt implant (HR: 5.12), presence of uveitic glaucoma (HR: 3.75) and poor preoperative visual acuity (HR: 1.55) were found to be significant.“These results support the use of an Ahmed glaucoma valve in patients at higher risk for chronic hypotony,” concluded the authors, who also mentioned that their study used “the largest prospectively collected dataset to date on tube shunt surgery analyzed at a per-patient level.”Click here for the journal source. Gedde AY, Huertas L, O’Brien R, et al. Chronic hypotony after tube shunt surgery: A pooled analysis of data from three randomized clinical trials. Am J Ophthalmol. November 19, 2025. [Epub ahead of print]. This article was developed by the editorial staff in conjunction with experts in the field. In the process, AI may have been among the editorial tools used to meet the goals of human editors, who approved all content.