SUPRACHOROIDAL MIGS

Brian Flowers, MD

Stents that shunt aqueous directly from the anterior chamber (AC) to the suprachoroidal space may reduce intraocular pressure (IOP) more than current minimally invasive glaucoma surgery (MIGS) procedures targeting the trabecular meshwork (TM), with fewer complications than traditional filtration surgery, Brian Flowers MD, Fort Worth, Texas, told the 2015 American Society of Cataract and Refractive Surgery Symposium in San Diego, USA.

While TM-based MIGS, including implants such as iStent (Glaukos), and procedures such as Trabectome (Neomedix), are very safe and patient-friendly, their potential for reducing IOP is limited by the capacity and potential blockages of the drainage system beyond the TM. In contrast, the suprachoroidal space has almost unlimited IOP-lowering capacity due to its large surface area and negative pressure gradient, Dr Flowers pointed out.

But high outflow capacity also presents risk for hypotony and unpredictable IOP, Dr Flowers noted. So the question becomes: is suprachoroidal MIGS safe? Several large-scale clinical trials suggest two new stents are not only safe and effective. It may even be possible to prevent or even rescue failures due to inadequate reservoir formation, Dr Flowers said.

IMPROVED PERFORMANCE

In a US FDA trial of 505 patients completed in March, the CyPass Micro-Stent (Transcend Medical) met its primary endpoint of lowering IOP 20 per cent from unmedicated preoperative values, and reducing IOP more than phacoemulsification alone for 24 months after surgery.

Similarly, a European study of 83 patients saw IOP reduced 35 per cent among patients whose preoperative pressure exceeded 21mmHg, with mean medications reduced from 2.2 to 1.0 at 24 months, and no sight-threatening complications or hypotony beyond one month. (Hoeh H. J Glaucoma. 2014 Oct 9. Höh H. Klin Mondbl Augenheilkd. 2014 Apr;231(4):377-81)

CyPass Vx uses viscoelastic injected through the stent to increase the size of the filtration reservoir. Injecting 30 microliters increased the aqueous lake volume 247 per cent, and injecting 60 microliters 321 per cent beyond the CyPass alone, generating reductions in mean IOP of an additional 24 per cent and 41 per cent respectively. This raises the possibility not only of improved performance, but possibly rescuing poorly performing implants, Dr Flowers said.

The iStent Supra (Glaukos) shows similar performance and safety, lowering IOP from 24.8 to 17.0 24 months after surgery. (Belda J. 2014 ESCRS, London)

In Dr Flowers’ experience, patients take slightly longer to recover from suprachoroidal stent surgery versus TM-based MIGS. However, the potential for greater IOP reduction may be worth it, and the lack of hypotony is reassuring, he added. “Suprachoroidal surgery may indeed be transformative,” he said.

bflowers@oafw2020.com