What is MIGS Glaucoma Surgery?
Minimally invasive glaucoma surgery or microinvasive glaucoma surgery (MIGS) is an alternative glaucoma surgery with minimal trauma, featuring small incisions, lower risk of complications during and after surgery, and faster recovery compared to conventional glaucoma surgery. Additionally, this surgical method can be performed even if conventional glaucoma surgery has failed.
Who is suitable for MIGS glaucoma surgery?
- Patients with early to moderate stage glaucoma
- Patients with open-angle glaucoma
- Patients who cannot control intraocular pressure despite using all glaucoma medications or have factors preventing eye drop use, such as allergies to glaucoma eye drops
Patients who are not suitable for MIGS surgery include those with shallow anterior chamber, inability to use eye drops or follow-up after surgery, or a history of allergy to Mitomycin C (MMC), which is a substance used in some types of MIGS surgery.
PreserFlo MicroShunt aqueous humor drainage tube, a MIGS surgical device
PreserFlo MicroShunt formerly known as MIDI-Tube, MIDI-Ray, MIDI-Arrow or InnFocus MicroShunt, is a device used in MIGS surgery developed by Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, USA
Characteristics and properties of PreserFlo MicroShunt
PreserFlo MicroShunt is a tube with drainage holes, approximately twice the size of an eyelash. It is made from poly(styrene-block-isobutylene-block-styrene) or SIBS, a material combining the properties of silicone rubber and polyurethane, meaning
- It is biostable
- Thermoplastic: flexible when heated and rigid when cooled
- Highly elastomeric, similar to natural rubber
With these properties, PreserFlo is soft and can bend to fit the shape of the eye when implanted. Theoretically, this helps reduce scarring and fibrosis at the scleral flap site. The device works by draining aqueous humor from the anterior chamber of the eye to the subconjunctival space, creating a bleb on the eye surface after surgery.
How does the PreserFlo MicroShunt drain aqueous humor?
PreserFlo MicroShunt is 8.5 millimeters long. The end of the tube inside the eye is beveled at 4.5 millimeters from the tip and has a 1-millimeter fin extending sideways. The outer diameter is 350 microns, and the drainage hole diameter is 70 microns. Both the tube and drainage hole of PreserFlo are smaller than other tube-based pressure-lowering devices. The specific design allows PreserFlo to self-regulate aqueous humor outflow, maintaining postoperative intraocular pressure above 5 millimeters of mercury.
Additionally, the tube end located about 6 millimeters from the limbus facilitates increased drainage of aqueous humor to the posterior part of the eye. PreserFlo can be used as a standalone implant or combined with cataract surgery in glaucoma patients ranging from early to very advanced stages.
PreserFlo MicroShunt received the CE mark in January 2012 and has been approved by Health Canada and the Therapeutic Goods Administration of Australia in 2021. In the United States, PreserFlo is still under study for FDA approval.
