Glaucoma drainage devices (GDD) have become essential in the management of glaucoma, but tube exposure is a potentially vision-threatening complication affecting 2.5% to 9.0% of cases. During Glaucoma Subspecialty Day on Saturday, Victoria M. Addis, MD, explained several key choices that surgeons can make to help lower the risk of tube exposure.
Potential causes. According to Dr. Addis, early tube exposure is often caused by dehiscence of the suture securing the material overlying the device. Late-onset exposure, however, is likely related to erosion of the overlying patch or conjunctiva. This degradation may be due to micromovements of the tube caused by blinking or ocular movements, increased tension at the overlying conjunctiva, or abnormal positioning of the tube.
Risk factors. Several risk factors for tube exposure have been proposed; among them are preoperative intraocular inflammation, female gender (possibly because of smaller fornices), diabetes, neovascular glaucoma, and a higher number of preoperative glaucoma medications. There is no solid evidence that patch graft material or GDD type affects the risk of tube exposure.
Location, location, location. The location of GDD placement, on the other hand, does matter. Devices that are implanted inferiorly are more likely to become exposed than those implanted superiorly. Dr. Addis explained that this is likely due to less available superficial tissue for implant coverage inferiorly, leading to increased tissue tension at the sutured sites.
Consider avoiding patch grafts completely. Some data suggest that partial-thickness scleral flaps and scleral tunnels carry a lower risk of tube erosion compared with implantation using patch grafts. One possible reason is that the host sclera acts as a vascular bed for releasing growth factors that enhance tissue viability.
At the end of her talk, Dr. Addis again emphasized the key takeaway from her presentation: “Implant superiorly whenever possible to decrease the risk of tube exposure.” —Keng Jin Lee, PhD
Financial disclosures: Dr. Addis: None.
Read more news from AAO 2019 and the Subspecialty Day meetings.