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MIGS not yet widely used in Asia-Pacific region
Based on the consensus statement on surgery for open-angle glaucoma by the World Glaucoma Association, trabeculectomy is the incisional procedure of choice in the previously unoperated eye.
However, the procedure is far from perfect. The two most common problems are failure and complications. Though trabeculectomy is a proven treatment to effectively lower IOP, the outcome is not always predictable as the complication rate is relatively high by our present day standard. Minimally invasive glaucoma surgery (MIGS) is one major challenge to this current gold standard procedure.
The definition of MIGS is still under development. In general, it should meet two criteria. Firstly, it is a surgical procedure that requires less incisional scale than trabeculectomy. Secondly, it shall cause significantly less vision-related complications. If one agrees on such criteria, then MIGS limits to ab interno angle surgery that either by-pass trabecular meshwork and connect aqueous directly to the Schlemm’s canal (iStent by Glaukos and Trabectome by Neomedix) or into the suprachoroidal space (CyPass by Transcend Medical). The ab externo procedure that can also fit into this definition is the Ex-PRESS (Alcon) device when using a corneal approach without conjunctival incision to create a scleral pocket and insert the implant through a small conjunctival incision.
If both smaller scale incision and safer surgery are preferred, a procedure like canaloplasty (iScience) may not be classified as MIGS, though it attains significant IOP reductions accompanied by an excellent short- and long-term safety profile. It involves a similar scale of incision to trabeculectomy; alternatively, canaloplasty may be classified as a non-penetrating procedure.
Perhaps another term should be coined, such as “safer filtering surgery” or “trabeculectomy alternatives” to encompass all newer glaucoma surgeries. The Ex-PRESS device with a regular conjunctival and scleral flap dissection would fit into this category. The ab externo approach for a suprachoroidal drainage device like the Gold Shunt (Solx) and perhaps all non-penetrating filtering procedures may also be classified into this category as well. At present, there is no consensus on these definitions. So, MIGS is still mixed with safer filtering surgery (SFS).
AP region
The Asia-Pacific region covers a wide area, with 61% of the world population. Glaucoma is inevitably one of the major health problems in the region. At present, MIGS and SFS are not commonly performed. Four main reasons why trabeculectomy is still the dominant form of surgery in the region are: 1) proven IOP lowering efficacy as none of the MIGS or SFS show significantly better hypotensive efficacy over trabeculectomy, 2) economic consideration as most MIGS and SFS are either costly or time-consuming and have no economic analysis to substantiate their superiority, 3) availability of these devices is poor or non-existing, and 4) physician and patient mindset.
However, many metropolitan areas are beginning to adopt these safer surgery alternatives in a non-uniform fashion. For example, canaloplasty, Ex-PRESS and the Gold Shunt are performed in Bangkok but not in the upcountry of Thailand. We see the value of these procedures that benefit select patients. The general adoption will follow the path of advanced technology IOLs, but selectively and gradually.
MIGS, SFS
MIGS and SFS are viable options with proven benefits to both surgeons and patients. As glaucoma patients are not uniform in their type, severity, expectation and individual characteristics, their surgeries cannot be one-size-fits-all. This also applies to surgeons with variable surgical expertise and interest. Perhaps the biggest group that will drive the use of MIGS is patients with coexisting cataract and mild to moderate glaucoma that may need cataract surgery. The surgeons seek the opportunity to add a glaucoma procedure that can be performed in the same sitting, but without compromising the visual outcome of cataract surgery. This is why we see so many studies where MIGS and SFS are being combined with phacoemulsification and IOL. The unclear answer is how much lens removal alone contributes to IOP-lowering and what percentage is from the additional MIGS or SFS. Because combined phaco-trabeculectomy is not always the procedure of choice, we will definitely see more and more MIGS and SFS in our practice.
MIGS and SFS address issues around filtering surgeries and should benefit our practices when used selectively.
References:
Bull H, von Wolff K, Körber N, Tetz M. Three-year canaloplasty outcomes for the treatment of open-angle glaucoma: European study results. Graefes Arch Clin Exp Ophthalmol. 2011;249(10):1537-1545.
Cioffi GA, Van Buskirk EM. Corneal trabeculectomy without conjunctival incision. Extended follow-up and histologic findings. Ophthalmology. 1993;100(7):1077-82.
Khaw PT, Chiang M, Shah P, Sii F, Lockwood A, Khalili A. Enhanced trabeculectomy – the Moorfields safer surgery system. Dev Ophthalmol. 2012;50:1-28.
Minckler DS, Hill RA. Use of novel devices for control of intraocular pressure. Exp Eye Res. 2009;88(4):792-798.
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Prin Rojanapongpun, MD, is associate professor and chairman, Department of Ophthalmology, Chulalongkorn University & Hospital, and a consultant at Bumrungrad International Hospital, Bangkok, Thailand. He can be reached at prinoph@gmail.com.
Disclosure: Dr. Prin Rojanapongpun has no relevant financial disclosures.