Ab Interno Approach to Subconjunctival Space: Materials and Biocompatibility of Minimally Invasive Collagen Glaucoma Implant
Narrative Responses:
Purpose
To describe the development of a novel, soft and permanent, minimally invasive ab interno collagen implant to optimize aqueous drainage to the subconjunctival space.
Methods
Preclinical and clinical testing was used to determine the optimal lumen size, length, diameter, tube rigidity, durability, flexibility and of the stent. Safe placement ab interno through sclera requires a flexible yet firm material that maintains shape without disrupting tissue planes. A cross linked collagen gelatin that is hard when dry but soft when hydrated was tested. Using a bending angle value as a reference, several tests were performed to compare bending forces between the gelatin stent and the most common material used to drain aqueous humor (silicone).
Results
Hydrolytic stability showed no evidence of hydrolytic degradation. A 10 year accelerated flow testing showed no changes in implant lumen or wall thickness. Data out to 6 years confirm that the implant remains stable and patent.Preclinical and human eye testing shows the implant does not seem to occlude inside the lumen and the implant material does not appear to cause any tissue reaction. The implant gives a flow of 0.02µl/sec or 1.2µl/min, (at 5 mmHg pressure gradient), thus providing around 6-8 mmHg flow resistance, which essentially eliminates hypotony. The high implant flexibility and small diameter avoid implant-tissue irritation and extrusion.
Conclusion
Subconjunctival drainage of aqueous fluid has been a cornerstone of glaucoma surgery for over a century. The ab interno placement of the gel stent offers a unique alternative for lowering intraocular pressure with a minimally invasive procedure, minimal conjunctival tissue disruption, restricted flow to avoid hypotony, and long term safety.