Cumulative dissipated energy during phacoemulsification is associated with bleb failure in eyes with prior trabeculectomy

Abstract

Introduction: Trabeculectomy is the most effective method of lowering the intraocular pressure (IOP) in patients with open-angle glaucoma refractory to pharmacological treatment or laser trabeculoplasty. Many phakic glaucoma patients later require cataract surgery after trabeculectomy. The purpose of this study is to determine factors that predict bleb failure after phacoemulsification. Methods: This retrospective, observational study included 33 eyes from 30 patients with open-angle glaucoma who had successful trabeculectomy with mitomycin (MMC) and subsequently underwent uncomplicated cataract surgery by means of clear corneal phacoemulsification performed by a single surgeon between 2006 and 2018. Bleb failure was defined as an eye that required the addition of two or more glaucoma medications or had an IOP > 21 mmHg at any follow-up visit more than one month after surgery. Kaplan-Meier analysis was conducted to visualize bleb survival over the two-year study period. Results: Ten eyes (30.3%) experienced bleb failure, at an average of 325 ± 254 days after phacoemulsification surgery. A further six eyes (18.2%) partially failed over this period. Blebs that remained fully functional (51.5%) two years after phacoemulsification surgery received lower total cumulative dissipated energy (CDE; 12.6 ± 7.2 versus 19.0 ± 7.7, P = 0.027). Conclusion: Higher levels of ultrasound energy at the time of cataract surgery, as reflected by CDE, are associated with bleb failure. Removing cataracts at a stage when the lens is less dense so that it will require less total ultrasound energy and allow shorter duration for surgery may benefit eyes with functioning filtering blebs.

Keywords

• Phacoemulsification
• Trabeculectomy
• Open-angle glaucoma
• Intraocular pressure