How MIGS are changing glaucoma treatment

Historically, first-line treatment of glaucoma has been topical therapy in a vast majority of cases with laser trabeculoplasty being favored when drops alone do not achieve target intraocular pressure (IOP).

Surgical intervention was traditionally reserved for advanced glaucoma cases in which other modes of treatment were determined to be insufficient. This is due to the fact that undergoing trabeculectomy can set the patient up for several adverse side effects.

Side effects from trabeculectomy may include hyphema, bleb leak, choroidal effusion, and infection.

Minimally (or micro-) invasive glaucoma surgery (MIGS) advancements have changed how glaucoma surgery is viewed due to their lower side effect profile compared to past glaucoma surgeries.

Previously from Dr. Casella: The dangers of starting and stopping glaucoma treatment

The iStent (Glaukos), for example, is inserted directly into the trabecular meshwork during a procedure combined with cataract surgery in order to facilitate trabecular drainage into Schelmm's canal.¹ This mechanism creates a way of bypassing part of the trabecular meshwork, which is the location of the most aqueous outflow and is the largest area of resistance to outflow.  Another MIGS device, XEN Gel Stent (Allergan) shunts fluid directly from the aqueous chamber to the subconjunctival space, thus creating a new drainage pathway.

Episcleral venous pressure is the limit of IOP reduction. This means that IOP cannot fall below episcleral venous pressure.¹ This principle may account for why some patients improve following implantation of iStent better than others.

Tapping into the suprachoroidal space

A previously untapped part of ocular anatomy with respect to glaucoma is the suprachoroidal space between the choroid and the sclera. This space is malleable and can accommodate fluid-such as aqueous humor.

Checking a patient’s IOP after blunt force trauma to the eyeball is important for determining whether or not a break occurred and if aqueous humor was let into the suprachoroidal space. If a break occurred, it can cause extremely low IOP and needs to be fixed.

Related: Helping patients better understand glaucoma

Creating a controlled breach between the anterior chamber and the suprachoroidal space is a new technique. CyPass (Alcon Inc.) is a stent that creates such a communication.¹ It is just over 6 mm in length and is inserted through a corneal incision.

In addition to being a potential space for the drainage of aqueous humor, the suprachoroidal space is also being studied as a potential drug delivery site for retinal diseases.² The FDA requires comparison of such novel technologies to conventional treatment such as topical medications.

With that said, it would not be far-fetched for a procedure such as these aforementioned or facsimiles thereof to become first-line preference one day. Insurance coverage for newer surgical procedures typically falls short if documented efficacy of conventional therapy seems sufficient. As more companies invest in research and development, our aging population will soon have more options for therapy and competition may drive down the cost of MIGS procedures.

Advancements help lessen burden

Scientists should continue to strive to discover therapies that rely less on patient participation, such as using drops-sometimes numerous drops-every day. Health care is trending toward lessening the burden on the patient, which should lead to better patient outcomes.

We likely all have patients who would benefit greatly from these novel surgical techniques.

References

1. Pillunat LE, Erb C, Jünemann AG, Kimmich F. Micro-invasive glaucoma surgery (MIGS): a review of surgical procedures using stents. Clin Ophthalmol. 2017 Aug 29;11:1583-1600.

2. Moisseiev E, Loewenstein A, Yiu G. The suprachoroidal space: from potential space to a space with potential. Clin Ophthalmol. 2016; 10: 173–178. 

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