Glaucoma surgery is a type of eye surgery performed to treat glaucoma, a group of diseases which affect the optic nerve, resulting in vision loss. Glaucoma is characterized by increased intraocular pressure (IOP). Most glaucoma surgeries seek to lower IOP by facilitating the escape of excess aqueous humor from the eye, while others decrease the production of aqueous humor.
Procedures that facilitate outflow of aqueous humor
Filtering procedures Filtering surgeries are the mainstay of surgical treatment to control intraocular pressure. An anterior sclerotomy or sclerostomy is used to gain access to the inner layers of the eye in order to create a drainage channel from the anterior chamber to the external surface of the eye under the conjunctiva, allowing 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.
Penetrating filtering surgeries Penetrating filtering surgeries are further subdivided into guarded filtering procedures, also known as protected, subscleral, or partial thickness filtering procedures (in which the surgeon sutures a scleral flap over the sclerostomy site), and full thickness procedures. Trabeculectomy is a guarded filtering procedure that removes part of the trabecular meshwork. Full thickness procedures include sclerectomy, posterior lip sclerectomy (in which the surgeon completely excises the sclera in the area of the sclerostomy), trephination, thermal sclerostomy (Scheie procedure), iridenclesis, and sclerostomy (including conventional sclerostomy and enzymatic sclerostomy). Anterior chamber paracentesis is a penetrating surgical procedure done to reduce intraocular pressure of the eye. It is limited in its time course and usually used to lower high eye pressure until a longer lasting pressure lowering procedure can be undertaken. This term is also used for a small entry made into the anterior chamber during eye surgery for access only, unrelated to intraocular pressure (IOP).
Non-penetrating filtering surgeries Non-penetrating filtering surgeries do not penetrate or enter the eye's anterior chamber. There are two types of non-penetrating surgeries: Bleb-forming and viscocanalostomy. Bleb forming procedures 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 surgically exposed by making a large, deep scleral flap. The inner wall of Schlemm's canal is stripped off after 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 excised, allowing subconjunctival filtration without actually entering the anterior chamber. In order to prevent wound adhesion after deep scleral excision and maintain good filtering results, it is sometimes performed with a variety of biocompatible spacers or devices, such as the Aquaflow collagen wick, ologen Collagen Matrix, or Xenoplast glaucoma implant. Viscocanalostomy is also an ab externo, major ocular procedure in which Schlemm's canal is surgically exposed by making a large, deep scleral flap. In the Viscocanalostomy procedure, Schlemm's canal is cannulated and viscoelastic substance injected (which dilates Schlemm's canal and the aqueous collector channels). Where wound modulation is needed to prevent closure of surgically created drainage channels, adjuvants such as the ologen collagen matrix implants may be used to facilitate healthy tissue regeneration. Scar formation at the site of excision or operation may block aqueous humor circulation, while healthy tissue regeneration will keep newly created drainage channels functional.
Laser trabeculoplasty
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 melanocytes 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 ALT. However, because SLT is performed using a laser with much lower power than ALT, 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 to 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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