Ab-Externo Glaucoma Drainage Device Tube Trimming: A Novel Technique

To describe a novel technique for ab-externo trimming the tube of a Glaucoma Drainage Device (GDD) in a patient with unilateral congenital glaucoma and localized endothelial decompensation.  

AKTINA Center, Athens Naval Hospital

A 19-year-old Caucasian female with a history of a GDD implanted in her left eye (OS) for primary congenital glaucoma (PCG) was referred to us due to corneal edema.  We diagnosed endothelial insufficiency related to the presence of a long GDD tube close to the posterior corneal surface. After unsuccessful attempts for intracameral tube trimming, we proceeded with an ab-externo approach, creating a clear corneal vertical incision over the tube (at a distance of 1 mm from the limbus) and the tube was subsequently trimmed through the vertical corneal incision with a fine Vannas scissors. The iris helped as a resistance plane. The patient was followed with Anterior Segment Spectral Domain Optical Coherence Tomography (AS-SS-OCT). 

One month after ab-externo GDD tube trimming, best corrected visual acuity (BCVA) improved from Hand Motion at 1 meter to 0.1 (Snellen decimal). Corneal edema resolved significantly. Central corneal thickness (CCT) was reduced from 692μm to 583μm and corneal thickness in the affected area over the GDD tube was reduced from over 700μm at presentation to below 600μm at 1 month after tube trimming. Subepithelial bullae resolved along with the patient’s symptoms. The cornea remains clear and the patient remains asymptomatic 2 years after the intervention.   

The presence of a GDD tube may cause corneal endothelial damage resulting in corneal decompensation. Trimming the GDD tube may prevent further endothelial failure, thus avoiding endothelial keratoplasty. In case traditional intracameral approach is unsuccessful, we propose an alternative ab-externo approach that may be easily and safely performed without sophisticated surgical instruments.