High Magnification in vivo Evaluation of the Mechanism of Failure of An Ex-PRESS Shunt Implanted Under the Sclera Flap

Abstract

To investigate the mechanism of fibrosis-related failure of an Ex-PRESS shunt implanted under the scleral flap in trabeculectomy. A patient with end-stage secondary open-angle glaucoma on his only functioning right eye was referred for glaucoma valve implantation. His right eye had undergone congenital cataract surgery in early childhood and posterior chamber lens implantation 20 years ago. During the last 18 months, the right eye underwent pars plana vitrectomy with silicone oil implantation, silicone oil removal, 2 sessions of cyclophotocoagulation, 2 failed trabeculectomies (one of them combined with Ex-PRESS shunt implantation under the scleral flap), and 4 trabeculectomy revisions. At presentation, the intraocular pressure varied between 47 and 52 mm Hg on maximal systemic and topical intraocular pressure-lowering medication. Serial limbus parallel scans made with the CAM-L cornea lens adapter of the Optovue Fourier-domain optical coherence tomograph revealed that the space between the inner surface of the scleral flap and the external orifice of the Ex-PRESS shunt was filled by scar tissue, and the scar tissue appeared to invade the lumen of the shunt. The findings suggest that failure of an Ex-PRESS shunt is not always caused by episcleral fibrosis but may also be caused by scar formation between the scleral flap and the implant, inside the surgical sclera tunnel.