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Minimally invasive glaucoma surgical devices: Are they ready for primetime use?

Srinivasan, Sathish FRCSEd, FRCOphth, FACS

Journal of Cataract & Refractive Surgery: July 2017 - Volume 43 - Issue 7 - p 867-868
doi: 10.1016/j.jcrs.2017.07.007
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The pessimist complains about the wind.

The optimist expects it to change.

The realist adjusts the sails.

—William Arthur Ward

Glaucoma is the leading cause of global irreversible blindness. It has been estimated that 60.5 million people were affected by primary open-angle glaucoma (POAG) globally in 2010.1,2 A recent metaanalysis of 50 population-based studies showed that the global prevalence of glaucoma for the population aged 40 to 80 years is 3.54%. In 2013, the number of people (aged 40 to 80 years) with glaucoma worldwide was estimated to be 64.3 million, increasing to 76.0 million in 2020 and 111.8 million in 2040.3 This represents a 74% increase in the global number of people with glaucoma from 2013 to 2040.

Although glaucoma is a complex and poorly understood neurodegenerative disorder, the primary goal of therapy is to lower the intraocular pressure (IOP), which is not only the most important risk factor for the progression of the disease but also the only modifiable one. Medical therapy is the primary treatment modality in glaucoma patients. On a fundamental level, IOP-lowering drugs have decreased pressure by reducing aqueous production or by enhancing aqueous outflow. Medical therapy for glaucoma fails because of progression of the disease resulting from inadequate IOP control or because of poor compliance and/or intolerance to topical therapy. In the 1990s, 3 new classes of IOP-lowering medications—namely prostaglandin analogues, topical carbonic anhydrase inhibitors, and topical α-2 agonists—were commercially introduced, which reduced the need for glaucoma surgery.4

The surgical treatment of glaucoma dates back to 1856, when von Graefe realized that iridectomy was an effective surgical treatment for acute glaucoma. In 1867, de Wecker described the technique of anterior sclerostomy in which a full-thickness scleral incision was made in the posterior limbus resulting in a “fistula” through which the aqueous egressed out of the anterior chamber.5 Following de Wecker’s sclerostomy, several modifications and techniques were introduced for creating a full-thickness fistula on the eye wall (ie, sclera) to drain aqueous to the subconjunctival space.6 In 1962, Sugar7 described guarded filtering surgery and later, in 1968, Cairns8 described this technique as trabeculectomy. Even today, trabeculectomy (with or without wound-healing modulation) is considered the gold standard filtration procedure by glaucoma surgeons.

The history of using devices to shunt aqueous dates back to 1876 when de Wecker described the use of gold wire as an implant for glaucoma patients. In 1954, Qadeer9 devised a plastic plate with drainage channels engraved in it. The plate was inserted subconjunctivally, and the head was placed in the anterior chamber. In 1969, Molteno10 described a new shunt that has since undergone several iterations. At present, several drainage shunts, valved and non-valved, are available to use in refractory glaucoma patients. All these devices have a tube that is inserted in the anterior chamber and a plate fixated on the scleral surface. The Tube Versus Trabeculectomy Study,11 a multicenter randomized clinical trial, showed that IOP reduction was similar between the 2 groups at 3 years.

Recently there has been much enthusiasm among glaucoma and anterior segment surgeons about microinvasive glaucoma surgery (MIGS), which includes the use of various drainage devices that seek to reduce IOP with less surgical risk compared with the traditional and more established glaucoma drainage procedures. Table 1 shows the currently available MIGS drainage devices. The potential advantages of MIGS procedures are that they are minimally invasive, have a higher safety profile, provide rapid patient recovery, are usually performed through an ab interno approach, can be performed during cataract surgery, and can be easily adapted by an anterior segment/cataract surgeon.

Table 1:
Comparison of the new generation of MIGS devices for glaucoma.

In this issue Fea et al. (pages 886–891) report the 2-year outcomes on the use of a Schlemm canal scaffold microshunt during cataract surgery in 92 eyes. Of the 67 patients who completed the 2-year follow-up, 64% were medication free. This multicenter retrospective study showed a 20% reduction in IOP from baseline at 2 years. Numerous studies have shown that cataract surgery reduces IOP in normal eyes and glaucomatous eyes. This reduction in IOP is more profound in eyes with acute or chronic angle-closure glaucoma.12 The IOP reduction in eyes with POAG is less pronounced, with a reported reduction of 13% after cataract surgery.13 Also, Hsia et al. (pages 879–885), in a prospective study that used anterior segment optical coherence tomography, found that in POAG cases, the IOP reduction was higher in eyes with narrow angles and that the preoperative IOP and anterior segment morphology were preoperative predictors of a postoperative IOP reduction.

At the time of this writing, there are only 2 prospective randomized clinical trials (RCT) comparing cataract surgery with cataract surgery and MIGS devices for IOP reduction.14,15 It is possible that MIGS will usher in a new era of surgical innovation for mild to moderate POAG. Until the time when there are more robust RCTs and long-term prospective data for each of these devices, we have to be cautious in their clinical use. History will be the judge.

Sathish Srinivasan, FRCSEd, FRCOphth, FACS


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© 2017 by Lippincott Williams & Wilkins, Inc.