1. Makati Medical Center Philippines David H. Gosiengfiao Jeffrey N. Racoma Mikhail Pador Santiago A. Sibayan * None of the authors have any financial interest to disclose

2. Introduction External migration of tube shunts is of particular concern in growing eyes. Management includes repositioning, adding a tube extender, replacement of the drainage device or additional glaucoma surgery. These frequently involve conjunctival surgery and consequent risks. We present a novel approach to the rescue of an intra-stromally migrated Ahmed tube.

3. The case An externally migrated Ahmed valve was found in a 7 year old who had previously undergone successful implantation. Examination revealed an uncontrolled IOP of 60 mmHg recalcitrant to medical management with the tip of the tube located intra-stromally, occluded by the posterior corneal lip. We used radiofrequency energy delivered through a sclerothalamotomy tip † (Oertli, Switzerland) to ablate the posterior lip, ensure the patency of the tract and re-establish flow. †not US-FDA approved

4. Sclerothalamotomy 1,2  Uses RF energy to create thalami in TM to lower IOP Tip dimensions ○ 300 um wide x 600 um high x by 1000 um long RF energy ○ 500 kHz ○ 7 W 1. B.Pajic, G.Pallas, G.Heinrich, M.Boenke. A novel technique of ab interno glaucoma surgery: follow up after 24 months. Graefe’s Arch Clin Exp Ophthal 2006 Jan;244(1):22-7 2. Operating Instructions CataRhex VC820100S. Oertli Instruments AG, Switzerland

5. The tube is externally migrated and no longer visible on gonioscopy Methodology

6. The anterior chamber was entered using a 1.6 mm keratome and filled with a cohesive viscoelastic

7. The internal lip was ablated using RF delivered via STT probe A spatula was used to ensure the patency of the tract

8. The Ahmed valve was re-primed resulting in a good bleb

9. Outcome The post-operative course was uneventful. 1 day after surgery, the eye was quiet with IOP at 12 mmHg. A mature bleb was observed around the body of the Ahmed valve. The IOP remained controlled at 16 mmHg at last follow up 1 year after surgery.

10. Discussion While outright replacement of the glaucoma drainage device or additional glaucoma surgery are possible, the advent of commercially available tube extenders has made them less desirable alternatives. Restoration of flow using tube extenders often leads to rapid IOP control to pre-migration levels because of the presence of an already mature pseudocyst or bleb around the plate. 3 Tube extension however, entails conjunctival dissection and may cause unwanted inflammation in close proximity to the bleb. Ab interno ablation using RF re-establishes flow while avoiding conjunctival dissection. 3. S.Sarkisian and P.Netland. Tube extender for Revision of Glaucoma Drainage Implants. J Glaucoma 2007;16:637-639

11. Ab-interno RF rescue of externally migrated shunt Pro’sCon’s  No conjunctival dissection  No conjunctival inflammation  Short procedure  Violates the anterior chamber  May release inflammatory cytokines from ablated tissue  Introduces energy

12. Conclusion An ab-interno approach to the rescue of an externally migrated glaucoma tube shunt may be a good alternative to conjunctival surgery Further studies should be conducted to assess long term success and lento- iridocorneal effects.