MIGS FUTURE BRIGHT

A range of ab-interno devices and techniques that provide moderate to excellent intraocular pressure (IOP) control with much less risk than traditional filtration or tube surgery are set to revolutionise glaucoma treatment, Iqbal “Ike” K Ahmed told the 2014 Symposium & Congress of the American Society of Cataract and Refractive Surgery (ASCRS) in Boston.

Collectively known as Microinvasive Glaucoma Surgery (MIGS), these include implants and instruments for enhancing physiological outflow, such as microstents and the trabectome, as well as shunts that open suprachoroidal channels or create scleral subconjunctival blebs. Together they fill the historical treatment gap between less effective but safe topical medications and lasers and effective but risky trabeculectomy and tube surgery, which typically are seen as treatments of last resort, Dr Ahmed said in the 2014 ASCRS Binkhorst Lecture.

“The promise of MIGS is that you can intervene early in the disease, reducing the morbidity of progression. This hopefully will reduce the need to expose ourselves and our patients to more aggressive surgical options when we are already too late in the disease process,” said Dr Ahmed, who is assistant professor at the University of Toronto where he also directs research, and clinical assistant professor at the University of Utah.

The effectiveness of some devices now in clinical tests rivals trabeculectomy, the current gold-standard for controlling IOP, without the long-term infection risk. If proven effective long-term these minimally invasive techniques could replace trabeculectomy altogether, he said. “I hope this will happen sooner rather than later. There is no reason why an ab-interno bleb cannot do just as well as an external bleb.”

Big role for cataract surgeons

That the Binkhorst Lecture, which usually examines cataract and refractive surgery, this year focused on glaucoma reflects the growing role for cataract surgeons in glaucoma treatment.

About 15 per cent to 20 per cent of patients undergoing cataract surgery also have glaucoma, Dr Ahmed noted. Phacoemulsification and lens extraction by itself often lowers IOP significantly and reduces the need for topical medications to control pressure. Adding MIGS technologies, such as the iStent (Glaukos) and Trabectome (NeoMedix), further reduces post-op IOP and medication needs, and these can be done with cataract surgery with very little additional risk.

“Any patient with glaucoma going to cataract surgery I think needs a really hard look for possibly combining [MIGS] with phaco. You’ve heard of a zero-sum game. This is a zero-loss game. We have very little to lose by trying an implant that does not preclude future [glaucoma] surgery, particularly in mild to moderate patients,” Dr Ahmed said.

The iStent is among the most studied of MIGS technologies and the first approved by the US FDA. Trials have shown that two iStents work better than one. Newer Schlemm’s bypass devices include the injectable iStent, which resembles a rivet and is delivered through the clear cornea with a 26-gauge injector. The Hydrus (Ivantis), a scaffolding device inserted in Schlemm’scanal, also has been shown to reduce IOP and greatly reduce medication use when placed in combination with phaco compared with phaco alone.

Studies also show that placing the iStent closer to a major collection channel further improves performance. Dr Ahmed recommended that surgeons interested in implanting Schlemm’s canal bypass devices familiarise themselves with the anatomy of aqueous veins and how to locate them in patients’ eyes, and place devices close to major outflow channels to maximise effectiveness. Familiarity with gonioscopy and visualising the angle are also essential skills for placing any type of outflow stent. Focal blood reflux after placing a Schlemm’s bypass stent is usually a good sign that it is properly placed close to an aqueous vein.

Suprachoroidal micro-stents create a channel from the angle to the suprachoidal space, taking advantage of the pressure gradient to drain aqueous into a collector lake, where it is resorbed. Early trials of the CyPass (Transcend) show it is effective in lowering IOP in patients with pre-op levels exceeding 21 mmHg. The iStent Supra also targets the suprachoroidal outflow channel.

The Xen implant (AqueSys) is an ab-interno device that creates an external subconjunctival bleb. But since it is delivered through an injector through a clear corneal incision, no external dissection is required, reducing long-term infection risk. Combined with an intraoperative injection of mytomycin C, Xen has been shown to reduce IOP by about 40 per cent over nine months, performance comparable to trabeculectomy.

Dr Ahmed sees Schlemm’s canal and suprachoroidal stents as low-risk options for mild to moderate glaucoma, with subconjunctival approaches possibly useful for full-spectrum disease. However, more data is needed to further support such indications. He is confident that MIGS will alter the traditional treatment algorithm. In addition to routine use in cataract surgery, the safety of MIGS will allow MIGS solo procedures, and possibly multiple MIGS procedures before resorting to trab or tubes.

Ike Ahmed: ike.ahmed@utoronto.ca