Eyeworld

EW GLAUCOMA 60 by Matt Young EyeWorld Contributing Editor A smarter way to reposition a glaucoma tube Minimally invasive method could help correct more than tube occlusion W hen a glaucoma drainage device (GDD) is not posi- tioned properly, there's a lot more at stake than tube occlusion. A malpo- sitioned tube risks corneal endothe- lial damage, chronic iritis, and cataract formation, according to Robert J. Campbell, F.R.C.S.C., oph- thalmology department, Queen's University, Kingston, Ontario. Dr. Campbell recommended a new technique to deal with GDD tube posterior malpositioning in a minimally invasive way. The report on the technique was published on- line in December 2010 in Clinical and Experimental Ophthalmology. "This technique is straightfor- ward to perform, and has success- fully maintained proper drainage device tube position during more than 1 year of follow-up," Dr. Campbell noted. Describing the technique Traditionally, repositioning a GDD tube has required an intricate process to redissect the scarred con- junctiva and patch graft and then remove and reinsert the tube, Dr. Campbell wrote. "This difficult and delicate dis- section carries a significant risk of intra-operative complications such as inadvertent tube damage, diffi- culty with tube reinsertion and wound healing problems, which may lead to tube or patch graft ex- posure," Dr. Campbell reported. "As an alternative, in some cases, simply shortening the tube via an internal approach may relieve tube contact with the cornea, lens or iris. How- ever, this technique may not effec- tively remove internal contact without excessively shortening the tube and risking tube extrusion from the anterior chamber." Dr. Campbell and colleagues described a technique that does not require tube shortening, but reposi- tions the tube in a less invasive manner. He described the technique, as implemented during a case of a pos- teriorly malpositioned GDD tube after an operation to remove silicone oil in a 41-year-old female patient, as follows in his report: The surgeon uses a crescent blade to make a 3-mm incision in the peripheral cornea over the tip of the tube. This occurs about 2 mm from the limbus. The incision should be created perpendicular to the tube direction, with the depth being half of the corneal thickness. Two side incisions are then cre- ated with a 22.5-degree blade. These incisions run radially from the ends of the first incision to the limbus. A half-thickness "reverse" corneal flap is then created with the crescent blade. This flap is made over the anterior chamber tube por- tion. "Fashioning the flap in a non- traditional 'reverse' direction allowed the dissection to extend to the peripheral anterior chamber and trabecular meshwork without dis- turbing the overlying conjunctiva or patch graft," Dr. Campbell wrote. The flap is retracted. "Using the GDD tube width of 0.6 mm as a guide, a small section (approximately 0.5 mm by 0.5 mm) of the sclera and trabecular mesh- work overlying the peripheral ante- rior chamber entry point of the tube was excised using the 22.5-degree blade," Dr. Campbell wrote. "This created a small space immediately anterior to the tube at its entry point into the anterior chamber. This al- lowed for anterior movement of the tube away from the iris." Right beside the tube, a 10-0 prolene suture should be passed through the deep corneal layer, about 1 mm away from the limbus. Now the surgeon should capture the tube. This involves passing the needle and suture under the posteri- orly misdirected tube and out of the anterior chamber through the over- lying deep corneal layer, opposite the tube. The surgeon can then pull the tube anteriorly by altering the suture tension. The tube needs to be lifted off the iris, yet remain far enough away from the corneal en- dothelium. The flap can then be reposi- tioned into place and secured with three 10-0 nylon sutures. Superficial corneal sutures should later be re- moved. The deep suture securing the tube can be left in place. Potential technique complica- tions do exist, including flap avul- sion. But overall, this is a safe and effective method to resolve posterior GDD tube malpositioning, Dr. Campbell concluded. David Gosiengfiao, M.D., Makati Medical Center, Makati City, Philippines, advocated ab interno rescue of an externally migrated glaucoma tube shunt in Posters on Demand at the 2009 ASCRS•ASOA Symposium & Congress in San Fran- cisco. He calls external migration of tube shunts a "particular concern in growing eyes." In one case of an externally mi- grated Ahmed valve (New World Medical, Rancho Cucamonga, Calif.) in a 7-year-old who previously un- derwent successful implantation, the child had uncontrolled IOP of 60, with the tip of the tube located in- trastromally, occluded by the poste- rior corneal lip. "We used radiofrequency energy delivered through a sclerothalamo- tomy tip (Oertli, Switzerland) to ab- late the posterior lip, ensure the patency of the tract and re-establish flow," Dr. Gosiengfiao reported. "One day after surgery, the eye was quiet with IOP at 12 mm Hg. A ma- ture bleb was observed around the body of the Ahmed valve. The IOP remained controlled at 16 mm Hg at last follow-up 1 year after surgery." EW Editors' note: Dr. Campbell has no fi- nancial interests related to his com- ments. Dr. Gosiengfiao has no financial interests related to his poster. Contact information Campbell: rob.campbell@queensu.ca Gosiengfiao: drgosh@yahoo.com February 2011 April 2011 A diagram of fluid movement in the eye. A new technique handles GDD malpositioning in a mini- mally invasive way, preventing corneal endothelial damage and other risks Source: National Eye Institute, National Institutes of Health

• Cover