NARROWER STENTS

Thomas W Samuelson MD

New narrower stents may make filtration surgery using subconjunctival blebs less invasive, and less prone to hypotony and other complications, while matching the unparalleled effectiveness of trabeculectomy in lowering intraocular pressure (IOP), Thomas W Samuelson MD, Minneapolis, told the ASCRS Glaucoma Day 2015 in San Diego, USA.

With a 210-micron outer diameter and a 45-micron lumen, three Xen (AqueSys) gel implants can fit inside the lumen of a Baerveldt tube, Dr Samuelson noted. The Xen is designed for ab interno delivery through an injector inserted through the cornea into the angle and on into the subconjunctival space, eliminating conjunctival dissection and its risks. An anti-fibrotic is injected to prevent scarring.

The Xen’s 45-micron lumen and 6.0mm length were calculated to provide enough flow to substantially lower IOP and enough resistance to minimise hypotony risk, Dr Samuelson said. Twelve-month follow-up data from 69 patients presented at ESCRS 2014 and American Glaucoma Society 2015 showed a mean IOP reduction of 44 per cent to 12.8mmHg from pre-op best medicated values. Six patients, or 8.6 per cent, experienced hypotony, or 6.0mmHg or less on day one, with one requiring anterior chamber re-inflation and none persisting past one month. With a 350-micron outer diameter, 70-micron lumen and 8.5mm length, the InnFocus MicroShunt is about one-third the inner diameter of conventional tubes, but is implanted similarly, requiring conjunctival dissection. The ab externo approach means more tissue disruption, but is more familiar to surgeons, Dr Samuelson said.

OUTFLOW MECHANISM

Early data from 22 patients followed for three years show mean IOP of 10.9mmHg, with a mean 0.5 medications and 73 per cent on no medication, down from 24.0mmHg on 2.8 medications before surgery with none on no medication. Ten per cent experienced hypotony after day one with all resolving spontaneously.

Both the Xen and MicroShunt bypass the entire physiological outflow mechanism, making them suitable for many types of glaucoma, Dr Samuelson said. Both also deliver aqueous well posterior to the limbus, promoting better bleb morphology and function.

These and other devices are making transscleral filtration surgery more standardised and less invasive, eliminating the need for sutures to control IOP, Dr Samuelson said.

He reported that the early non-published results are very promising. But widespread adoption will likely depend on their long-term safety and effectiveness mitigating hypotony, and the success of competing canal-based glaucoma procedure.

Thomas W Samuelson: twsamuelson@mneye.com