MIGS arrives in Western Victoria
There is finally some relief in sight for glaucoma sufferers in Western Victoria with the arrival of Minimally Invasive Glaucoma Surgery (MIGS).
Dr Vincent Lee recently delivered a lecture on ‘MIGS Treatment Algorithms’ to a group of 15 Optometrists from the region. The lecture, on 20 March 2018, was organized through Optometry Victoria Director, Mr Jayson Ward of Warrnambool and Portland Eye Care, and held at the Lady Bay Resort in Warrnambool. Attending Optometrists received 3 CPD points, as approved by Optometry Victoria.
As Dr Lee explained, this class of surgery has been steadily evolving over the last 20 years and will soon make a difference to thousands of patients in our region. As its name implies, the big advantage of MIGS lies in the fact that there is a great reduction in the incisional surgery required as compared to traditional filtration operations such as trabeculectomy and insertion of drainage tubes that many glaucoma sufferers eventually require.
Similar to traditional surgery, MIGS targets both excessive production of aqueous as well as diminished drainage. However, due to advances in technique made possible by breakthroughs in technological development, MIGS procedures take a much shorter operating time and carry considerably less risk. And in terms of success rates, MIGS compares well with traditional surgery.
Presently, there are three new MIGS procedures that have been approved in Australia, with a fourth soon to be introduced. These procedures involve the implantation of devices that enhance outflow of aqueous, but each implant targets different outflow pathways.
The iStent Inject (Glaukos) was the first MIGS device to be approved in Australia in 2016 and provides a direct route for aqueous into Schlemm’s canal. It is the smallest medical device approved for use in humans and consists of a heparin-coated non-ferromagnetic, titanium stent measuring 360 microns by 230 microns. It is inserted into Schlemm’s canal through the trabecular meshwork, essentially bypassing it. Two stents are inserted in the nasal quadrant where there is an increased density of aqueous drainage veins thereby maximizing the efficacy of the shunt.
The Hydrus Microstent is a MIGS stent made of a super-elastic, biocompatible alloy (nitinol) that has been used in over 1 million implants to date. It is an intracanalicular scaffold - a type of support structure inserted into the primary fluid canal (known as Schlemms canal) to allow blocked fluid to flow more freely, therefore reducing eye pressure. It is often used in moderate glaucoma. The Hydrus microstent can be described under the category of MIGS procedures known as canaloplasty, in which the primary drainage canal inside the eye is improved in its function.
The Xen Gel Stent (Allergan) is a 6mm long gelatin stent. It is inserted via an ab interno approach through the scleral wall from the anterior chamber to the subconjuctival space. It results in a new trans-scleral aqueous outflow pathway into a low lying extraocular filtration bleb, similar to a mini-trabeculectomy.
To measure efficacy, clinical trials measured magnitude of unmedicated IOP reduction, proportion of patients not requiring medication and magnitude of decrease in medication use.
All three of these procedures result in a significant reduction in IOP (20-50%) as well a significant decrease in medication burden (50-85%). In addition, 40-80% of patients remained medication free postoperatively for the follow up periods of between 2-3 years. Follow up is continuing and there are numerous ongoing trials investigating these and other results.