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| [[Glaucoma]] is a group of diseases affecting the [[optic nerve]] that results in [[vision loss]] and is frequently characterized by raised [[intraocular pressure]] (IOP). There are many glaucoma [[surgery|surgeries]], and variations or combinations of those [[surgery|surgeries]], that facilitate the escape of excess [[aqueous humor]] from the eye to lower [[intraocular pressure]], and a few that lower [[IOP]] by decreasing the production of [[aqueous humor|aqueous]]. | | [[Glaucoma]] is a group of diseases affecting the [[optic nerve]] that results in [[vision loss]] and is frequently characterized by raised [[intraocular pressure]] (IOP). There are many glaucoma [[surgery|surgeries]], and variations or combinations of those [[surgery|surgeries]], that facilitate the escape of excess [[aqueous humor]] from the eye to lower [[intraocular pressure]], and a few that lower [[IOP]] by decreasing the production of [[aqueous humor|aqueous]]. |
| ==Surgery== | | ==Surgery== |
| ===Procedures that Facilitate Outflow of Aqueous Humor===
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| ====Laser Trabeculoplasty====
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| A ''trabeculoplasty'' is a modification of the [[trabecular meshwork]]. ''[[Laser]] trabeculoplasty'' (LTP) is the application of a [[laser]] beam to burn areas of the trabecular meshwork, located near the base of the [[iris]], to increase fluid outflow. LTP is used in the treatment of various open-angle glaucomas. The two types of [[laser]] trabeculoplasty are ''[[argon]] [[laser]] trabeculoplasty'' (ALT) and ''selective [[laser]] trabeculoplasty'' (SLT). As its name suggests, [[argon]] [[laser]] trabeculoplasty uses an [[argon]] [[laser]] to create tiny burns on the trabecular meshwork. Selective [[laser]] trabeculoplasty is newer technology that uses a [[Nd:YAG laser]] to target specific cells within the trabecular meshwork and create less thermal damage than ALT. SLT shows promise as a long term treatment. In SLT a [[laser]] is used to selectively target the [[melanocyte]]s in the trabecular meshwork. Though the mechanism by which SLT functions is not well understood, it has been shown in trials to be as effective as the older [[Argon]] [[Laser]] Trabeculoplasty. However, because SLT is performed using a much lower power [[laser]], it does not appear to affect the structure of the trabecular meshwork (based on [[electron microscopy]]) to the same extent, so retreatment may be possible if the effects from the original treatment should begin wear off, although this has not been proven in clinical studies. ALT is repeatable to some extent with measurable results possible.
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| ====Iridotomy====
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| An ''[[iridotomy]]'' involves making puncture-like openings through the [[iris (anatomy)|iris]] without the removal of [[iris]] tissue. Performed either with standard [[surgery|surgical]] instruments or a [[laser]], it is typically used to decrease [[IOP|intraocular pressure]] in patients with angle-closure glaucoma. A ''[[laser]] peripheral [[iridotomy]]'' (LPI) is the application of a [[laser]] beam to selectively burn a hole through the [[iris]] near its base. LPI may be performed with either an [[argon]] [[laser]] or [[Nd:YAG laser]].
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| ====Iridectomy====
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| An ''[[iridectomy]]'', also known as a ''corectomy'' or ''[[surgical]] [[iridectomy]]'', involves the removal of a portion of [[iris]] tissue.<ref name="Cline">Cline D; Hofstetter HW; Griffin JR. ''Dictionary of Visual Science''. 4th ed. Butterworth-Heinemann, Boston 1997. ISBN 0-7506-9895-0</ref> A basal [[iridectomy]] is the removal of [[iris]] tissue from the far periphery, near the [[iris]] root; a peripheral [[iridectomy]] is the removal of [[iris]] tissue at the periphery; and a sector [[iridectomy]] is the removal of a wedge-shaped section of [[iris]] that extends from the [[pupil]] margin to the [[iris]] root, leaving a keyhole-shaped [[pupil]].
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| ===Filtering Procedures: Penetrating vs. Non-penetrating===
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| Filtering [[surgery|surgeries]] are the mainstay of [[surgery|surgical]] treatment to control [[IOP|intraocular pressure]].<ref>Jacobi PC, Dietlein TS, Krieglstein GK. "Technique of goniocurettage: a potential treatment for advanced chronic open angle glaucoma." ''Br J Ophthalmol''. 1997 Apr;81(4):302-7. PMID 9215060.</ref> An ''[[anterior]] sclerotomy'' or ''sclerostomy'' is used to gain access to the inner layers of the eye<ref name="pmid10150851">{{cite journal| author=Berlin MS, Yoo PH, Ahn RJ| title=The role of laser sclerostomy in glaucoma surgery. | journal=Curr Opin Ophthalmol | year= 1995 | volume= 6 | issue= 2 | pages= 102-14 | pmid=10150851 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=10150851 }} </ref><ref name="pmid9215060">{{cite journal| author=Jacobi PC, Dietlein TS, Krieglstein GK| title=Technique of goniocurettage: a potential treatment for advanced chronic open angle glaucoma. | journal=Br J Ophthalmol | year= 1997 | volume= 81 | issue= 4 | pages= 302-7 | pmid=9215060 | doi= | pmc=PMC1722166 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=9215060 }} </ref> in order to create a drainage channel from the [[anterior chamber]] to the external surface of the eye under the [[conjunctiva]], allowing [[aqueous humor|aqueous]] to seep into a bleb from which it is slowly absorbed. Filtering procedures are typically divided into either penetrating or non-penetrating types depending upon whether an intraoperative entry into the [[anterior chamber]] occurs.
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| Penetrating filtering [[surgery|surgeries]] are further subdivided into guarded filtering [[procedure]]s, also known as protected, subscleral, or partial thickness filtering procedures (in which the [[surgeon]] [[suture]]s a [[sclera]]l flap over the sclerostomy site, and full thickness procedures. ''[[Trabeculectomy]]'' is a guarded filtering [[procedure]] that removes of part of the trabecular meshwork. Full thickness [[procedure]]s include sclerectomy, posterior lip sclerectomy (in which the surgeon completely [[excision|excises]] the [[sclera]] on the area of the sclerostomy, trephination, thermal sclerostomy (Scheie procedure), iridenclesis, and sclerostomy (including conventional sclerostomy and [[enzymatic]] sclerostomy).
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| Non-penetrating filtering [[surgery|surgeries]] do not penetrate or enter the eye's [[anterior chamber]]<ref name="pmid12048520">{{cite journal| author=Hamard P, Lachkar Y| title=[Non penetrating filtering surgery, evolution and results]. | journal=J Fr Ophtalmol | year= 2002 | volume= 25 | issue= 5 | pages= 527-36 | pmid=12048520 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=12048520 }} </ref><ref name="pmid11880725">{{cite journal| author=Lachkar Y, Hamard P| title=Nonpenetrating filtering surgery. | journal=Curr Opin Ophthalmol | year= 2002 | volume= 13 | issue= 2 | pages= 110-5 | pmid=11880725 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=11880725 }} </ref>. There are two types of non-penetrating [[surgery|surgeries]]: Bleb-forming and viscocanalostomy. Bleb forming [[procedure]]s include ab externo [[trabeculectomy]] and deep sclerectomy. Ab externo [[trabeculectomy]] (AET) involves cutting from outside the eye inward to reach [[Schlemm's canal]], the trabecular meshwork, and the [[anterior chamber]]. Also known as non-penetrating [[trabeculectomy]] (NPT), it is an ab externo (from the outside), major [[ocular]] [[procedure]] in which [[Schlemm's canal]] is [[surgery|surgically]] exposed by making a large and very deep [[sclera]]l flap. The inner wall of [[Schlemm's canal]] is stripped off after [[surgery|surgically]] exposing the canal. Deep sclerectomy, also known as nonpenetrating deep sclerectomy (PDS) or nonpenetrating [[trabeculectomy]] is a filtering [[surgery]] where the internal wall of [[Schlemm's canal]] is [[excision|excised]], allowing sub[[conjunctiva]]l filtration without actually entering the [[anterior chamber]]<ref name="pmid15005582">{{cite journal| author=Lachkar Y, Neverauskiene J, Jeanteur-Lunel MN, Gracies H, Berkani M, Ecoffet M et al.| title=Nonpenetrating deep sclerectomy: a 6-year retrospective study. | journal=Eur J Ophthalmol | year= 2004 | volume= 14 | issue= 1 | pages= 26-36 | pmid=15005582 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=15005582 }} </ref>; it is commonly performed with the Aquaflow® collagen wick. ''Viscocanalostomy'' is also an ab externo, major [[ocular]] [[procedure]] in which [[Schlemm's canal]] is [[surgery|surgically]] exposed by making a large and very deep [[sclera]]l flap. In the VC procedure, [[Schlemm's canal]] is [[cannulation|cannulated]] and [[viscoelastic]] substance [[injection|injected]] (which [[mydriasis|dilates]] [[Schlemm's canal]] and the aqueous collector channels).
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| ===Other Surgical Procedures===
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| ''Goniotomy'' and ''trabeculotomy'' are similar simple and directed techniques of microsurgical dissection with mechanical disruption of the trabecular meshwork. Gonotomy [[procedure]]s include [[surgery|surgical]] goniotomy and [[laser]] goniotomy. A [[surgery|surgical]] goniotomy involves cutting the fibers of the trabecular meshwork to allow [[aqueous humor|aqueous fluid]] to flow more freely from the eye. [[Laser]] goniotomy is also known as goniophotoablation and [[laser]] trabecular ablation. In many patients suffering from [[congenital]] glaucoma, the [[cornea]] is not clear enough to visualize the [[anterior chamber]] angle. Although an [[endoscopic]] goniotomy, which employs an [[endoscope]] to view the [[anterior chamber]] angle, may be performed, a trabeculotomy which accesses the angle from the exterior surface of the eye, thereby eliminating the need for a clear [[cornea]], is usually preferred in these instances. A specially designed probe is used to tear through the trabecular meshwork to open it and allow fluid flow.
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| ''Tube-shunt [[surgery]]'' or ''drainage implant [[surgery]]'' involves the placement of a tube or [[glaucoma valve]]s to facilitate [[aqueous humor|aqueous]] outflow from the [[anterior chamber]]. Trabeculopuncture uses a Q switched [[Nd:YAG laser]] to punch small holes in the trabecular meshwork with<ref name="pmid4022580">{{cite journal| author=Epstein DL, Melamed S, Puliafto CA, Steinert RF| title=Neodymium: YAG laser trabeculopuncture in open-angle glaucoma. | journal=Ophthalmology | year= 1985 | volume= 92 | issue= 7 | pages= 931-7 | pmid=4022580 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=4022580 }} </ref><ref name="pmid121373">{{cite journal| author=van der Zypen E, Fankhauser F| title=The ultrastructural features of laser trabeculopuncture and cyclodialysis. Problems related to successful treatment of chronic simple glaucoma. | journal=Ophthalmologica | year= 1979 | volume= 179 | issue= 4 | pages= 189-200 | pmid=121373 | doi= | pmc= | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=121373 }} </ref>. ''Goniocurretage'' is an "ab interno" (from the inside) [[procedure]] that used an instrument "to scrape [[pathological]]ly altered trabecular meshwork off the [[sclera]]l [[sulcus]]"<ref name="pmid9215060">{{cite journal| author=Jacobi PC, Dietlein TS, Krieglstein GK| title=Technique of goniocurettage: a potential treatment for advanced chronic open angle glaucoma. | journal=Br J Ophthalmol | year= 1997 | volume= 81 | issue= 4 | pages= 302-7 | pmid=9215060 | doi= | pmc=PMC1722166 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=9215060 }} </ref>. A [[Surgery|surgical]] ''cyclodialysis'' is a rarely used procedure that aims to separate the [[ciliary body]] from the [[sclera]] to form a communication between the suprachoroidal space and the [[anterior chamber]].<ref name="Cline"/> A ''cyclogoniotomy'' is a [[surgery|surgical]] [[procedure]] for producing a cyclodialysis, in which the [[ciliary body]] is cut from its attachment at the [[sclera]]l spur under [[gonioscopy|gonioscopic]] control.<ref name="Cline"/>
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| A ''[[ciliarotomy]]'' is a [[surgery|surgical]] division of the [[ciliary body|ciliary zone]] in the treatment of glaucoma<ref name="Cline"/>.
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| ==== Canaloplasty ====
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| Canaloplasty is a nonpenetrating procedure utilizing microcatheter technology. To perform a canaloplasty, an [[incision]] in made into the eye to gain access to [[Schlemm's canal]] in a similar fashion to a viscocanalostomy. A microcatheter will circumnavigate the canal around the [[iris]], enlarging the main drainage channel and its smaller collector channels through the injection of a sterile, gel-like material called [[viscoelastic]]. The catheter is then removed and a [[suture]] is placed within the canal and tightened. By opening the canal, the [[IOP|pressure inside the eye]] may be relieved, although the reason is unclear since the [[Schlemm's canal|canal (of Schlemm)]] does not have any significant fluid resistance in glaucoma or healthy eyes. Long-term results are not available.
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| ===Procedures that Decrease Production of Aqueous Humor===
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| Certain cells within the eye's [[ciliary body]] produce [[aqueous humor]]. A [[ciliary body|ciliary]] destructive or cyclodestructive [[procedure]] is one that aims to destroy those cells in order to reduce [[IOP|intraocular pressure]]. ''Cyclocryotherapy'', or cyclocryopexy, uses a freezing probe. Cyclophotocoagulation, also known as transscleral cyclophotocoagulation, [[ciliary body]] ablation, cyclophotoablation, and cyclophototherapy, uses a [[laser]]. ''Cyclodiathermy'' uses heat generated from a high frequency [[alternating current|alternating electric current]] passed through the tissue,<ref name="Cline"/> while ''cycloelectrolysis'' uses the chemical action caused by a low frequency [[direct current]].<ref name="Cline"/>
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| ==Glaucoma Drainage Implants==
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| There are also several different glaucoma drainage [[implant]]s. These include the original Molteno [[implant]] (1966), the Baerveldt tube shunt, or the valved [[implant]]s, such as the Ahmed [[glaucoma valve]] [[implant]] and the later generation pressure ridge Molteno [[implant]]s. 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 [[implant]]ed underneath the [[conjunctiva]] to allow flow of [[aqueous humor|aqueous fluid]] out of the eye into a chamber called a bleb. The Express mini-[[implant]] is currently being used as a modification of the standard [[trabeculectomy]] technique, and is a non-valved conduit between the [[anterior chamber]] and the space under the [[sclera]]l flap<ref name="express">Maris PJ, Jr., Ishida K, Netland PA. Comparison of trabeculectomy with Ex-PRESS miniature glaucoma device implanted under scleral flap. J Glaucoma 2007 January;16(1):14-9 </ref>.
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| * The first-generation Molteno and other non-valved [[implant]]s sometimes require the ligation of the tube until the bleb formed is mildly [[fibrosis|fibrosed]] and water-tight<ref name="VicrylTie">Molteno AC, Polkinghorne PJ, Bowbyes JA. The vicryl tie technique for inserting a draining implant in the treatment of secondary glaucoma. Aust N Z J Ophthalmol. 1986 Nov;14(4):343-54
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| [http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=PubMed&list_uids=3814422&dopt=Citation.]
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| </ref>This is done to reduce postoperative hypotony -- sudden drops in postoperative intraocular pressure (IOP).
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| * Valved [[implant]]s such as the Ahmed [[glaucoma valve]] attempt to control postoperative hypotony by using a mechanical valve. Studies show that in severe cases of glaucoma, double plate Molteno [[implant]]s are associated with lower mean [[IOP]] in the long term compared to the Ahmed [[glaucoma valve]] <ref name="AhmedCompare">
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| Ayyala RS, Zurakowski D et al. Comparison of double-plate Molteno and Ahmed glaucoma valve in patients with advanced uncontrolled glaucoma.
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| Ophthalmic Surg Lasers. 2002 Mar-Apr;33(2):94-101.[http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=PubMed&list_uids=11942556&dopt=Citation].
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| </ref>
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| * Second and third generation Molteno [[implant]]s incorporate a biological [[valve]] and studies show considerable improvement in postoperative outcome over the older style Ahmed and Molteno [[implant]]s.
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| The ongoing scarring over the [[conjunctiva]]l dissipation segment of the shunt may become too thick for the [[aqueous humor]] to filter through. This may require preventive measures using anti-[[fibrosis|fibrotic]] medication like [[5-fluorouracil]] ([[5-FU]]) or [[mitomycin-C]] (during the procedure), or additional [[surgery]].
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| ==References== | | ==References== |