By Netan Choudhry, M.D, FRCS, Manjool Shah, M.D., and Jennifer George
Affecting nearly 65 million people worldwide, glaucoma is now one of the leading causes of blindness. The disease often results in irreversible damage even before the onset of any symptoms and though it has been identifiable for centuries, the cause, in most cases, is still unknown. Over the last few decades, however, several new and exciting options have emerged in the treatment of glaucoma. MIGS or Microinvasive Glaucoma Surgery has proven to be a safer alternative for patients leading to shorter recovery times than the traditional glaucoma surgeries such as trabeculectomy.
There are several varieties of glaucoma, each with a unique treatment approach. In primary open-angle glaucoma, eyecare providers prescribe eye drops that aim to reduce the production of fluid in the eye, while simultaneously assisting its natural drainage channels to improve outflow. The ultimate goal is to lower pressure within the eye, thereby preventing the progression of glaucomatous injury and irreversible vision loss. Ophthalmologists may also turn to laser surgery to combat glaucoma. Lasers can be used to stimulate cellular changes in the trabecular meshwork that can improve outflow. Until now, the last resort for glaucoma patients was surgery, such as trabeculectomy, or implantation of a glaucoma drainage device. In both options, a bypass for alternative drainage of fluid from within the anterior chamber of the eye is created.
While effective, surgical procedures such as trabeculectomy are invasive. Non-MIGS procedures (ie: trabeculectomy and tube shunts) involve substantial conjunctival dissection, a prolonged recovery period and a relatively higher rate of vision loss compared with MIGS procedures. Furthermore, these surgeries have a relatively high failure rate, thereby leading to re-operations. By contrast, MIGS procedures require less dissection and are prone to less serious side effects with faster recovery.
MIGS devices, while still under development, target different parts of the aqueous outflow pathway. Targets for MIGS devices include direct bypass of the trabecular meshwork into Schlemm’s canal, the suprachoroidal space, and under the conjunctiva. There are theoretical advantages and disadvantages to all three approaches and research is being carried out to determine how these outflow pathways can be modified to help in achieving lowered intraocular pressure.
The most commonly used MIGS device, the iStent®, shunts fluid directly from the anterior chamber, past the trabecular meshwork and into the aqueous outflow system via Schlemm’s canal. Glaukos®, maker of the iStent, has several additional versions of its trabecular bypass device under review. The HydrusTM Microstent by Ivantis also targets the canal of Schlemm, like the iStent. The CyPass® microstent bypasses the traditional outflow pathway, instead of shunting fluid into the suprachoroidal space underneath the sclera. This pathway is increasingly being recognized as an important component of the outflow system. Another device under active investigation is the XEN Gel Stent by AqueSys. Like a trabeculectomy or glaucoma drainage device, this minimally invasive stent shunts fluid into the subconjunctival space but without the need for extensive conjunctival dissection.
Often, MIGS procedures can be combined with cataract surgery to achieve additional intraocular pressure lowering and improved visual function. Numerous studies have demonstrated the intraocular pressure lowering effect of cataract surgery alone in a variety of glaucoma subtypes, and the addition of MIGS procedures may increase this effect. It is important to note that since these procedures do not, in general, result in excessive scarring of the conjunctiva, the door for traditional glaucoma surgery in the future is not closed.
MIGS devices and surgical approaches may be less invasive, but also may not provide the same degree of pressure lowering as traditional glaucoma surgeries. Proponents of MIGS procedures suggest that the role of MIGS would be to provide earlier surgical options for patients with mild or moderate glaucoma, in order to help them get off eye drops or delay a more aggressive surgical approach for a few years. The proliferation of MIGS technologies represents a potential paradigm shift in the approach to glaucoma disease management.
While traditional glaucoma surgeries could remain in the armamentarium of the glaucoma surgeon for patients in advanced stages of the disease, these new technologies may offer another option for many patients before it reaches that point. A great deal of research is taking place in this exciting area of ophthalmology and time will tell if a new era in glaucoma management is upon us.
