Glaucoma Surgical Devices
Robert Noecker, MD, MBA
Glaucoma surgical procedures are continuing to evolve and many new devices that are under investigation or have been introduced into the market have continued the trend towards increasing safety, less surgical manipulation and use of existing physiologic pathways. There has been a trend toward procedures that can be performed in conjunction with cataract surgery with minimal additional anesthesia and minimal effects on refractive error.
Glaucoma surgery has arguably lagged in innovation as compared to cataract and refractive surgery over the past several decades. Trabeculectomy has remained the gold standard procedure despite the unpredictability and risk associated with intra-operative variation and patient healing. Glaucoma drainage devices (Baerveldt, Ahmed, Molteno) have remained the most commonly used second line devices and have remained largely unchanged over the past 30 years.
The trend toward less invasive glaucoma procedures began with the introduction of canaloplasty, endocyclophotocoagulation (ECP), trabectome and the Express minishunt. All of these devices are currently available in the United States market and have been in use for a number of years.
ECP (EndoOptiks) has shown improved outcomes with the improvement in fiber optics and laser technology, as well as treatment algorithms that have allowed for more aggressive treatment and better IOP lowering outcomes. ECP also is the one procedure that works on the inflow aspect of aqueous flow through selective ablation of the ciliary epithelium and can be used in conjunction with outflow procedures. Canaloplasty (iScience Interventional) has emerged as an effective procedure that lowers IOP over an extended period of time through augmenting the eyes natural outflow apparatus. Canaloplasty appears to lower IOP through the creation of a Descemet’s window and dilation and tensioning the trabecular meshwork using a unique microcatheter system with the placement of a suture in Schlemm’s canal. Felt by some surgeons to be technically challenging, the clinical data around IOP lowering is compelling.
Trabectome (Neomedix) is a thermal cautery device that is used to ablate a quadrant of trabecular meshwork under direct gonioscopic visualization. The procedure is relatively quick to perform in which as section of the trabecular meshwork is removed to facilitate outflow and is frequently performed in conjunction with cataract surgery. It appears to lower IOP marginally well.
The Ex-press glaucoma filtration device (Alcon) has improved upon the traditional trabeculectomy by standardizing the procedure and providing restriction to outflow in the intraoperative and immediate post-operative period. This stainless steel mini-shunt is placed under a scleral flap and makes filtering surgery more reproducible and less traumatic. Another advantage is that the Ex-PRESS procedure appears to provide faster recovery and less post-operative intervention than traditional trabeculectomy surgery.
There are several new devices currently being evaluated in clinical trials in the United States. These newer glaucoma procedures can be grouped into those that improve upon traditional outflow bypass procedures. Those that increase outflow through a trabecular bypass strategy and those that lower IOP by increasing outflow through the uveoscleral pathway.
Another new device that is used for filtering surgery and currently in clinical trials, is the AqueSys Implant. This device is implanted in the eye from an ab interno approach to create a pathway to the subconjunctival space. A preloaded needle is inserted through the cornea, across the anterior chamber, and into the subconjunctival space. The implant keeps the outflow pathway open to the subconjunctival space and remains permanently or until it is removed.
iStent trabecular micro-bypass (Glaukos) is a small titanium stent that is used as a trabecular bypass device that allows aqueous fluid to drain directly into Schlemm’s canal. The device is placed through a clear corneal incision into Schlemm’s canal under gonioscopic visualization. Current trials are investigating placement of more than one iStent to further lower pressure. This device is used for targeted for use in early to moderate glaucoma, frequently in combination with cataract surgery.
Hydrus (Ivantis) is a similar intracanalicular implant, that is placed is placed into Schlemm’s Canal under gonioscopic visualization. This device is larger and opens more clock hours of Schlemm’s canal. It may work by both creating a relatively large opening through the traditional source of flow blockage and may provide a scaffolding effect within Schlemm’s canal. It too is in clinical trials to evaluate use both alone and in conjunction with cataract surgery.
CyPass (Transcend Medical) is in clinical trials to evaluate its safety and efficacy in lowering IOP via the suprachoroidal space. It is a microstent that is placed into the supraciliary space in order to increase uveoscleral outflow. It is implanted through a clear corneal incision and can be combined with cataract surgery.
Another device that is placed into the suprachoroidal space is the Gold micro-shunt (SOLX). This 3 x 6 mm device made of goal that is less than 0.1 mm thick and is very biocompatible. The device is placed into the supraciliary space from an external approach through a 3 mm incision in the sclera. It is in clinical trials in a population that has failed prior glaucoma procedures.
Newer devices are lowering the bar for performing glaucoma surgery and appear to hold promise for less invasive procedures with associated faster visual recovery and effective IOP lowering. As more become available to glaucoma surgeons, surgery will become more customizable to the specific physiologic deficiencies in each eye.