Editing Glaucoma (section)

====Glaucoma drainage implants====
{{Main|Glaucoma valve}}
The first glaucoma drainage implant was developed in 1966.<ref>{{cite web |url=http://www.glaucoma.org.nz/memberFiles/Eyelights11-05.pdf |title=Eyelights Newsletter: About Glaucoma New Zealand |publisher=Glaucoma.org |access-date=20 February 2014 |url-status=live |archive-url=https://web.archive.org/web/20150113141756/http://glaucoma.org.nz/memberFiles/Eyelights11-05.pdf |archive-date=13 January 2015 }}</ref> Since then, several types of implants have followed on from the original: the Baerveldt tube shunt, or the valved implants, such as the Ahmed glaucoma valve implant or the ExPress Mini Shunt and the later generation pressure ridge Molteno implants. These are indicated for glaucoma patients not responding to maximal medical therapy, with previous failed guarded filtering surgery (trabeculectomy). The flow tube is inserted into the anterior chamber of the eye, and the plate is implanted underneath the conjunctiva to allow a flow of aqueous fluid out of the eye into a chamber called a [[bleb (medicine)|bleb]].

*The first-generation Molteno and other nonvalved implants sometimes require the ligation of the tube until the bleb formed is mildly fibrosed and water-tight.<ref name=VicrylTie>{{cite journal | vauthors = Molteno AC, Polkinghorne PJ, Bowbyes JA | title = The vicryl tie technique for inserting a draining implant in the treatment of secondary glaucoma | journal = Australian and New Zealand Journal of Ophthalmology | volume = 14 | issue = 4 | pages = 343–354 | date = November 1986 | pmid = 3814422 | doi = 10.1111/j.1442-9071.1986.tb00470.x | doi-access = free }}
</ref> This is done to reduce postoperative hypotony—sudden drops in postoperative intraocular pressure.
* Valved implants, such as the Ahmed glaucoma valve, attempt to control postoperative hypotony by using a mechanical valve.
* Ab interno implants, such as the Xen Gel Stent, are transscleral implants by an ab interno procedure to channel aqueous humor into the non-dissected Tenon's space, creating a subconjunctival drainage area similar to a bleb.<ref>{{cite journal | vauthors = Lewis RA | title = Ab interno approach to the subconjunctival space using a collagen glaucoma stent | journal = Journal of Cataract and Refractive Surgery | volume = 40 | issue = 8 | pages = 1301–1306 | date = August 2014 | pmid = 24943904 | doi = 10.1016/j.jcrs.2014.01.032 }}</ref><ref>{{cite web|title=Xen Gel Stent|url=http://www.aquesys.com/xen.aspx|website=AqueSys|access-date=27 June 2015|url-status=dead|archive-url=https://web.archive.org/web/20150629022832/http://aquesys.com/xen.aspx|archive-date=29 June 2015}}</ref> The implants are transscleral and different from other ab interno implants that do not create a transscleral drainage, such as iStent, CyPass, or Hydrus.<ref>{{cite news|title=Advances in Glaucoma Filtration Surgery|url=http://glaucomatoday.com/2014/04/advances-in-glaucoma-filtration-surgery|access-date=27 June 2015|publisher=Glaucoma Today|url-status=live|archive-url=https://web.archive.org/web/20150629194028/http://glaucomatoday.com/2014/04/advances-in-glaucoma-filtration-surgery|archive-date=29 June 2015}}</ref><ref>{{cite journal | vauthors = Otarola F, Virgili G, Shah A, Hu K, Bunce C, Gazzard G | title = Ab interno trabecular bypass surgery with Schlemm´s canal microstent (Hydrus) for open angle glaucoma | journal = The Cochrane Database of Systematic Reviews | volume = 2020 | issue = 3 | pages = CD012740 | date = March 2020 | pmid = 32147807 | pmc = 7061024 | doi = 10.1002/14651858.cd012740.pub2 }}</ref>

The ongoing scarring over the conjunctival dissipation segment of the shunt may become too thick for the aqueous humor to filter through. This may require preventive measures using antifibrotic medications, such as 5-fluorouracil or mitomycin-C (during the procedure), or other nonantifibrotic medication methods, such as collagen matrix implant,<ref>{{cite journal | vauthors = Rosentreter A, Schild AM, Dinslage S, Dietlein TS | title = Biodegradable implant for tissue repair after glaucoma drainage device surgery | journal = Journal of Glaucoma | volume = 21 | issue = 2 | pages = 76–78 | date = February 2012 | pmid = 21278584 | doi = 10.1097/IJG.0b013e3182027ab0 | s2cid = 40206358 }}</ref><ref name="Capsule excision and Ologen implant">{{cite journal | vauthors = Rosentreter A, Mellein AC, Konen WW, Dietlein TS | title = Capsule excision and Ologen implantation for revision after glaucoma drainage device surgery | journal = Graefe's Archive for Clinical and Experimental Ophthalmology = Albrecht von Graefes Archiv für Klinische und Experimentelle Ophthalmologie | volume = 248 | issue = 9 | pages = 1319–1324 | date = September 2010 | pmid = 20405139 | doi = 10.1007/s00417-010-1385-y | s2cid = 10384646 }}</ref> or biodegradable spacer, or later on create a necessity for revision surgery with the sole or combinative use of donor patch grafts or collagen matrix implant.<ref name="Capsule excision and Ologen implant"/>