MIGS LOOKS PROMISING

Micro-Invasive Glaucoma Surgery (MIGS) is a promising approach for patients whose disease isn’t severe enough to require trabeculectomy, but for whom drops aren’t quite doing the job either.

This was one of the key messages from Ike Ahmed MD, an assistant professor of ophthalmology at the University of Toronto. He is one of Canada’s leading authorities on glaucoma and spoke at the recent annual Walter Wright Day – Update in Ophthalmology in Toronto, Canada.

“We have a gap between medications and trabeculectomy. MIGS is an alternative for that big space that’s empty right now which is mild-to-moderate glaucoma,†he told EuroTimes in an interview.

However, at this point, MIGS is most commonly used for mild-to-moderate glaucoma in patients who undergo cataract removal rather than being used for glaucoma on its own.

MIGS entails implanting a small device designed to reduce intraocular pressure by enhancing aqueous flow. It spares the conjunctiva, does not destroy surrounding tissues, and preserves the trabecular meshwork. Compared to traditional surgery it is a much safer option with rapid recovery.

Because it is a surgical approach, it comes with surgical risks, albeit small – and the risk-benefit profile hasn’t been fully evaluated, Dr Ahmed said. But in glaucoma patients undergoing phaco, the incision is already there and consequently MIGS performed in that environment shouldn’t represent an increased risk for that population.

MIGS procedures are all ab interno and each device enhances flow through one of three routes: Schlemm’s canal, uveal sclera outflow, or enhancing subconjunctival flow. There have been substantial advances in the development of MIGS just in the past few years because of improved technology and better understanding of surgical intervention in terms of physiology, Dr Ahmed said.

At this point five devices have been developed, though only two are on the market internationally: the iStent (Glaukos) and the Trabectome (NeoMedix). Both devices enhance flow via Schlemm's canal, albeit in slightly differently ways, and the number of stents in an eye could vary. Studies show on average, patients end up with an IOP of about 15mmHg on after MIGS.

“MIGS is not a procedure to lower IOP to 10 or so, nor is it a procedure for very advanced disease where patients need single-digit IOPs,†Dr Ahmed said. Patients who get the implants can achieve IOPs in the mid-to-low teens. “It would be great if we could get them down to 12 or so with no medications, but there is a limit in terms of what MIGS can do based on normal physiology,†he said.

Improving compliance However, if a medication is added, sometimes even lower levels can be attained. Generally, successful outcome for MIGS is determined by the ability to reduce the number of a patient’s medications. Many glaucoma patients take multiple types of drops throughout the day, and compliance is often poor. If the number of medications can be reduced, the better the compliance may be with the remaining eye drops they may need.

Another reason MIGS is performed along with phaco is that phaco is often associated with lowering of IOP. There can be some advantages with phaco and MIGS working together, he said. Studies to date show MIGS to be a very safe procedure, though issues can arise that accompany any implantable device. Some of those problems can include fibrosis around the device, or internal lumen blockage from fibrin, blood or pigment.

“These are all issues with the healing process of the eye and need to be combated as devices evolve in their development. Also, as surgeons we need good technique and [need to] be as atraumatic as possible. Certain patients might fail or will have limited success because of those reasons,†Dr Ahmed said.

As one of the few Canadian glaucoma surgeons to perform MIGS, Dr Ahmed sees the approach as something that doesn’t have to be limited to sub-specialists. General ophthalmologists could perform the procedures. No special equipment is needed aside from a gonioscopy lens and surgical microscope.

A review of glaucoma procedures and devices was published recently in Ophthalmology (July 2011). In “Novel Glaucoma Procedures, a report by the American Academy of Ophthalmologyâ€, authors reported on devices and procedures that are either approved for use in the US or are in phase-III clinical trials, and included the iStent and Trabectome. The authors noted these show promise as alternative treatments for lowering IOP in open-angle glaucoma, but said there is not yet enough information on how devices compared to each other in terms of efficacy. Nor is it known yet how they compare to other procedures such as trabeculectomy. Randomised controlled trials are needed.

Additional MIGS devices in the pipeline are Cypass (Transcend), Hydrus (Ivantis) and the Aquesys. The Hydrus is a Schlemm’s canal device, with the Cypass enhancing flow through the suprachoroidal space, while the Aquesys is intended to work via the subconjunctival space.

MIGS has the potential to change the algorithm ophthalmologists use when treating glaucoma patients, Dr Ahmed said. Right now, less invasive approaches for milder glaucoma cases start with one and then multiple medications, followed by SLT. Later, with disease progression, patients may undergo trabeculectomy. Some patients undergo either a second trabeculectomy or a drainage tube implant.

In future, that algorithm could change to starting with one medication or SLT. Patients who need a lower target pressure or whose disease progress could then be treated with one MIGS device and then even another if needed. Perhaps conventional outflow may be targeted first, with movement to alternative outflow pathways as needed. After that, either the ExPress device (Alcon) could be offered, or trabeculectomy or a tube.

Overall, MIGS could allow for less invasive and less traumatic procedures overall, and help preserve natural ocular physiology. But right now, their use is primarily for those in-between glaucoma patients who undergo phaco.