4th October 2016
MIGS: A Paradigm Shift for Glaucoma
Traditionally, glaucoma treatment has started off with drops, followed by laser treatment, and then trabeculectomy or tube shunt as the disease advances. With one or more types of antihypertensive drops being the customary first line of care, surgery has been reserved for more advanced, uncontrolled glaucoma. But that is changing.
Micro Invasive Glaucoma Surgery
Micro invasive glaucoma surgery (MIGS) is an emerging treatment option that can decrease dependency on medication. Also known as minimally invasive glaucoma surgery, MIGS utilizes microscopic devices and small incisions. This group of procedures is being developed to reduce complications that are possible with traditional glaucoma surgeries.
In most cases of open-angle glaucoma, elevated IOP is thought to be due in part to an abnormality in the trabecular meshwork. It cannot drain aqueous humor properly. MIGS devices provide various bypasses to reroute aqueous. Currently, two are available in the market—the iStent trabecular microbypass and the CyPass Micro-Stent. These are the first in a wave of devices lined up for FDA approval.
Despite the variation of MIGS devices, they share similar qualities:
- Microincisional and conjunctival-sparing
- Minimally disruptive to ocular anatomy
- Moderate IOP-lowering efficacy
- High safety profile
- Rapid recovery
MIGS with Cataract Surgery
In the US, a high percentage of cataract patients have open-angle glaucoma (OAG). In fact, more than 20% of cataract surgery eyes are on a minimum of one glaucoma drop. Both the iStent and CyPass systems are implanted at the time of cataract surgery. They increase aqueous flow and offer a high safety profile to patients with mild to moderate OAG.
This titanium trabecular micro-bypass system is FDA approved for the treatment of mild to moderate OAG in conjunction with cataract surgery. Placed in Schlemm’s canal, the snorkel-like shunt allows aqueous to bypass the trabecular meshwork. Only 1 mm in length, the stent is the smallest medical device surgically implanted into a human. At conclusion of cataract surgery, the iStent is often placed into the nasal angle, which is easily accessible via a temporal cataract surgery incision. An independent international clinical study, published by the Journal of Cataract and Refractive Surgery, showed the iStent had a 36% reduction in IOP and an 86% reduction in medication usage over a three-year period. The US IDE Pivotal study showed the following safety profile.
CyPass Micro-Stent (Alcon)
This device very recently received FDA approval for treatment of mild to moderate primary OAG. It creates a channel for aqueous fluid to flow out of the anterior chamber and into the suprachoroidal space. The stent is a 0.5 mm diameter tube that is 6.35 mm in length. It is inserted at the conclusion of cataract surgery into a space between the iris and scleral spur. FDA approval was based on the COMPASS Study, the largest MIGS study to date with two-year follow-up of over 500 mild to moderate glaucoma patients undergoing cataract surgery. Of the CyPass patients, 73% achieved 20% or more decrease in IOP. Also, 61% of CyPass patients achieved IOP between 6 and 18 mmHg at their 24-month exam without medication. This same study found the following safety profile.
Xen Gel Stent (Allergan)
The Xen device is a permanent, collagen-derived, cross-linked gelatin shunt. It is about 6 mm long and the width of a human hair. This micro device is injected into the eye across the anterior chamber, through the sclera, and into the sub-Tenon space. In this position, it creates an outflow of aqueous from the anterior chamber to the subconjunctival space. The Xen does not yet have FDA approval, but early data suggests it may lower IOP more than the iStent.
Hydrus Microstent (Ivantis)
Roughly the size of an eyelash, the Hydrus Microstent is made from a super-elastic, biocompatible alloy (nitinol alloy). The 8 mm long stent is placed through the trabecular meshwork into Schlemm’s canal where it acts as a scaffold. Clinical trials are underway.
The Microshunt is a device that shunts aqueous from the anterior chamber to a sub-conjunctival/sub-Tenon flap. It has been cleared by the FDA for clinical study.
The two FDA approved MIGS devices (iStent and CyPass) are intended for use in conjunction with cataract surgery. They are for patients with mild to moderate OAG who are on one or two glaucoma medications.
High safety profiles allow these procedures to be used earlier in the disease processes than traditional glaucoma surgeries. Contraindications include angle-closure, advanced glaucoma and other forms of secondary glaucoma.
Although not a cure, MIGS is changing the landscape of glaucoma surgery. The safety and low maintenance of these innovative devices give properly selected patients the opportunity to reduce dependency on one or more glaucoma drops. This can be especially helpful when topical medicines are ineffective due to expense, unwanted side effects, or poor compliance.
Our experience with the iStent has been positive. This procedure is currently available at all of our office locations except Albuquerque, NM, Anchorage, AK and Olympia, WA. We are excited about the future of MIGS and look forward to comparing safety and efficacy of new procedures and devices as they are developed.
If you have questions about MIGS, please feel free to contact our optometric physicians. We are always happy to help.