A minimally invasive ab interno collagen stent may be a viable alternative to other glaucoma drainage methods, according to a review to be published in the Journal of Cataract & Refractive Surgery.
In the review, author Richard A. Lewis, MD, explained that the XEN gel stent (Aquesys) — developed to avoid hypotony and optimize aqueous drainage to the subconjunctival space — has undergone extensive preclinical and animal testing, and clinical trials are now in progress.
“Determining the optimum size of the device lumen to avoid hypotony while maximizing long-term outflow is crucial. Specific characteristics are critical in designing an implant. These include implant material, length, diameter, flexibility, stability and biocompatibility of the implant,” Lewis wrote.
The XEN gel stent is a hydrophilic tube made of porcine gelatin cross-linked with glutaraldehyde. Bovine and porcine versions of the implant have been developed, and both have been successfully cross-linked to become stable, permanent implants, according to Lewis.
“Hydrolytic stability shows no evidence of hydrolytic degradation. The biocompatibility properties of gelatin are well established and do not cause a foreign-body reaction,” he wrote.
In human eye testing, the implant material remained mobile, with no adhesions or fibrosis, for 6 months in the subconjunctival space, according to Lewis.
Three 6-mm implants with varying internal diameters for IOP control were designed.
“The implant is hard when dry but is designed to be soft and flexible when hydrated. After being implanted in the eye, it becomes soft within 1 to 2 minutes,” Lewis wrote. “In its natural hydrated state, the implant is straight but adapts to the tissue shape, becoming tissue-conforming. Implant flexibility is an important criterion to avoiding migration and potential erosion.”
Disclosure: Lewis received financial support from Aquesys as a consultant.