title: Ab interno approach to the subconjunctival space using a collagen glaucoma stent.
abstract: This review considers a minimally invasive ab interno approach to glaucoma filtration surgery. Glaucoma filtration surgery can be defined as an attempt to lower intraocular pressure (IOP) by the surgical formation of an artificial drainage pathway from the anterior chamber to the subconjunctival space. Subconjunctival drainage of aqueous fluid has been a cornerstone of glaucoma surgery for more than a century. Varying techniques have been deployed to provide access to this space. Yet, despite numerous innovations in filtering surgery to achieve safe IOP reduction, too many short-term and long-term complications are associated with this surgery. This article describes the development of a new, soft, and permanent ab interno collagen implant (XEN gel stent) to optimize aqueous drainage to the subconjunctival space. Specific characteristics are critical in designing such an implant. Determining the optimum size of the device lumen to avoid hypotony while maximizing long-term outflow is crucial. Other topics discussed include material, length, diameter, flexibility, stability, and biocompatibility of the implant. Preclinical and human eye testing shows that the implant does not seem to occlude inside the lumen and the implant material does not appear to cause tissue reaction in the eye. The ab interno placement of the stent offers an alternative for lowering IOP with a minimally invasive procedure, minimum conjunctival tissue disruption, restricted flow to avoid hypotony, and long-term safety.
  
  
  BACKGROUND
  Dr. Lewis received financial support from Aquesys, Inc. as a consultant.
authors.affiliation: From a private practice, Sacramento, California, USA. Electronic address: rlewiseyemd@yahoo.com.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Lewis
mesh_terms: D001082:Aqueous Humor / Q000502:physiology; D003094:Collagen; D003228:Conjunctiva / Q000601:surgery*; D018463:Filtering Surgery / Q000379:methods*; D005901:Glaucoma / Q000503:physiopathology / Q000601:surgery*; D020327:Glaucoma Drainage Implants; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology; D019060:Minimally Invasive Surgical Procedures; D015607:Stents; D014065:Tonometry, Ocular
chemical_list: D003094:Collagen