By Dr. Brit Cooper-Jones

Glaucoma – a progressive optic neuropathy (a disease that damages the nerve that enables sight) – is a leading cause of blindness, affecting more than 400,000 Canadians. While early-stage glaucoma has no noticeable signs or symptoms, many patients who have been diagnosed with glaucoma are fearful about the possibility of one day losing their sight – something so critical to our ability to perceive and interact with the world around us, to say nothing of our independence and ability to continue doing the activities we love.

So what happens in glaucoma? Elevated pressure inside the eye (called intraocular pressure) is thought to contribute to gradual and progressive damage to the optic nerve (the nerve that enables sight). The condition starts asymptomatically, but this does not mean that damage is not occurring.

As the damage to the optic nerve becomes more advanced, it eventually starts to impact sight and can ultimately lead to blindness. Fortunately, however, we can significantly slow the progression of the disease – and thus preserve patients’ sight for as long as possible – by giving treatments that help to lower the pressure inside the eye.

The current treatments for glaucoma may vary based upon the severity of a patient’s disease. In early-stage glaucoma, patients are typically prescribed eye drops that help to lower the pressure inside the eye (in turn slowing the rate of damage to the optic nerve). Patients with early-stage glaucoma may also receive laser surgery.

However, while these treatments effectively slow the progression of glaucoma, none of them can stop it completely. As a result, additional forms of treatment become necessary as time goes on. This often starts with the addition of different types of eye drops. And, as patients’ glaucoma becomes more severe, many go on to require more invasive eye surgeries (for example, implantation of a device to divert fluid outside the eye to help manage the intraocular pressure). These more invasive eye surgeries may be done independently or at the same time as cataract surgery (for patients who have both glaucoma and cataracts).

The good news is that the currently available treatments do work well. But there is always the question of how we can do better – it is at the root of medical innovation – and, in the field of glaucoma treatment, it has led to the latest surgical development: minimally invasive glaucoma surgery (also known as “MIGS” for short).

What is MIGS? Or should we say what are MIGS? Because “MIGS” actually represents a class of many different newer minimally invasive surgical options. In fact, there are currently 11 MIGS devices and procedures approved for use in Canada, although one – the CyPass Micro-Stent – was voluntarily withdrawn from the global market in August 2018.

“Minimally invasive” refers to devices and procedures that are less invasive (meaning that that require no dissection of the sclera and minimal or no manipulation of the conjunctiva), leading to the hypothesis that MIGS devices and procedures may be safer and/or have a faster recovery time than the traditional more invasive surgeries. However, is this truly the case? Have MIGS been shown to be a better option than alternative treatments, or is it still too soon to tell? If they are better, is one MIGS device or procedure superior to others? And is public health care funding warranted?

To help answer these questions, and to guide decisions about MIGS and where they fit in the glaucoma clinical care pathway, decision-makers and the health care community turned to CADTH — an independent agency that finds, assesses, and summarizes the research on drugs, medical devices, tests, and procedures — to find out what the evidence says.

CADTH conducted a Health Technology Assessment (HTA) that looked at the comparative clinical effectiveness and safety, as well as the comparative cost-effectiveness, of various MIGS devices and procedures versus each other and versus alternative current glaucoma treatments. In the HTA, the perspective and experiences of patients were also considered, alongside ethical issues and implementation issues involved in using MIGS for the treatment of adults with glaucoma. Treatment options were considered both independently as well as in combination with cataract surgery (for patients with both glaucoma and cataracts). The Health Technology Expert Review Panel (HTERP) then developed recommendations based on the findings from CADTH’s report.

Overall, it was concluded that, at the present time, there is simply not enough evidence to know whether MIGS offers a benefit beyond what is already offered with current treatment options. From a clinical effectiveness standpoint, a safety standpoint, and a cost-effectiveness standpoint, the results were inconclusive.

HTERP acknowledged that there is a potential role for MIGS for the treatment of adults with glaucoma; however, more research is still needed to determine the optimal use of MIGS and what its role should be in the glaucoma clinical care pathway.

To view CADTH’s full report, see: https://cadth.ca/optimal-use-minimally-invasive-glaucoma-surgery-health-technology-assessment

And if you would like to learn more about CADTH, visit cadth.ca, follow us on Twitter @CADTH_ACMTS, or speak to a Liaison Officer in your region: cadth.ca/Liaison-Officers.

Dr. Brit Cooper-Jones, MD is a Knowledge Mobilization Officer at CADTH.