Complications and Management of Glaucoma Filtering Treatment & Management

Updated: Nov 17, 2021
  • Author: Madeleine Puig, MD; Chief Editor: Hampton Roy, Sr, MD  more...
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Approach Considerations

No cure is available for glaucoma, but, in some cases, disease progression can be controlled. Even with effective treatment, patients must have regular eye examinations. Treatment often continues for the patient's lifetime.

Lowering the intraocular pressure (IOP) is the focus of treating patients with glaucoma. Lowering IOP is done to a level to limit further optic nerve damage; this level is referred to as the target pressure and is determined by the ophthalmologist based on the structural and functional examination of each patient. The target IOP differs for each patient, and a patient's target pressure may change during the course of a lifetime. The IOP may be controlled by medical or surgical therapy.


Medical Therapy

For open-angle glaucoma, the ophthalmologist may prescribe medications to lower IOP. Topical or oral medications, inserts (waferlike strips of medication that are put in the corner of the eye), or eye ointments can be used.

Topical Medications

Topical medications lower IOP by increasing outflow of aqueous humor from the eye or decreasing the amount of aqueous humor produced. Systemic adverse effects can be reduced and higher intraocular concentration of medication can be achieved with topical medications compared to oral drugs. Topical medications include the following:

  • Miotics  (eg, pilocarpine, carbachol) - Increase the outflow of aqueous humor from the eye through trabecular meshwork. This is achieved by the miotic effect of cholinergic drugs that leads to contraction of ciliary muscles and thus reduced resistance to outflow via the trabecular meshwork. Due to its short duration of effect, miotics need to be applied 3 to 4 times daily. Miotics are third line medications due to adverse effects, the burden of frequent application, and relatively small effect on lowering IOP. [29]  
  • Prostaglandin analogs  (eg, latanoprost) - Increase the outflow of aqueous humor through secondary uveoscleral route, with little to no effect on trabecular outflow pathways. [30]  
  • Epinephrine compounds  - Increase the outflow of aqueous humor from the eye through trabecular and uveoscleral routes. [31, 32] Possible mechanisms include the effect of epinephrine on endothelial cells or ciliary body tone. [2]
  • Beta-blockers  (eg, timolol, betaxolol) - Reduce the amount of aqueous humor produced in the eye. [33] Beta blockers can be used as monotherapy in early stages of glaucoma as first line drugs.
  • Local Carbonic anhydrase inhibitors - Reduce the amount of aqueous humor produced in the eye
  • Alpha-adrenergic agonists  (eg, clonidine, apraclonidine, brimonidine) - Reduce the amount of aqueous humor produced in the eye. Alpha 2 agonists can cross the blood brain barrier and induce systemic hypotension, which in turn lowers IOP. [34] Brimonidine has also been shown to facilitate aqueous outflow via uveolscleral pathways. [35]

Oral Medications

Oral medication can control IOP. Carbonic anhydrase inhibitors (CAIs), which slow the production of aqueous humor in the eye, are the most common. Examples include acetazolamide and methazolamide. Systemic CAIs have been shown to reduce IOP by 20% to 30%. [2]

Many of the same medications used to treat patients with open-angle glaucoma are used to treat patients with angle-closure glaucoma. Angle-closure glaucoma can cause IOP to rise quickly. To rapidly lower the pressure to prevent vision loss, the ophthalmologist may administer a hyperosmotic agent. The effects of this drug last only 6 to 8 hours; therefore, it is not used for the long-term management of glaucoma.

Adverse Effects

Any medication, including eye drops, may have adverse effects. Most adverse effects are not serious and usually resolve, and not every patient experiences them. However, patients with glaucoma must carefully adhere to their prescribed treatments and discuss any adverse effects with their ophthalmologist. If an adverse effect is serious enough or intolerable, the patient and the ophthalmologist may decide to change the medication or the type of treatment.

Possible adverse effects associated with glaucoma medication include the following: (see Glaucoma Medications for further details)

  • Stinging or redness of eyes
  • Blurred vision
  • Headache
  • Bradycardia or bronchospasm
  • Changes in sexual desire
  • Mood changes
  • Tingling of fingers and toes
  • Drowsiness
  • Loss of appetite
  • Change of iris color (in patients with light-colored eyes taking prostaglandin analogs)

Surgical Therapy

For some patients, surgery might be the best option. Surgery may be performed first or after attempts to lower IOP with medications are tried. Several types of surgery are available to treat patients with glaucoma. The type and the severity of the glaucoma, the patient's other ocular diseases, and the patient's health are all considerations in selecting the type of operation. Surgery may be performed by using a laser or with more conventional approaches, such as incisional surgery, viscocanalostomy, or tube shunt placement.

Laser surgery

Trabeculoplasty is most often used for patients with open-angle glaucoma. A laser is applied to stimulate the trabecular endothelial cells to pump more efficiently to transport aqueous humor out of the eye. Furthermore, contraction of the burns induced by the laser increases the spaces in the adjacent (untreated) tissue, resulting in increased outflow in the drainage area of the eye (the trabecular meshwork).

Iridotomy is another laser surgery that is frequently used to treat patients with angle-closure glaucoma. The laser makes a small hole in the iris to allow the aqueous humor to flow more freely within the eye from the posterior to anterior chamber.

In cyclophotocoagulation (CPC), a laser is used to freeze selected areas of the ciliary body (the part of the eye that produces the aqueous humor) to reduce fluid production. This procedure may be used to treat more advanced or aggressive cases of glaucoma.

Most laser surgeries can be performed in the ophthalmologist's office or in an outpatient surgical facility. Because patients usually have little discomfort, eye drops are used to numb the eye for topical anesthesia. Recovery is quick, and patients may have local eye irritation, but they can usually resume their normal activities within 1 to 2 days.

Incisional surgery

Filtering surgery (trabeculectomy) is usually performed in a hospital or in an outpatient surgical center with local anesthesia and sometimes sedation. Using delicate instruments, the ophthalmic surgeon removes a tiny piece of the sclera, leaving a tiny hole where aqueous humor can flow into a space between the conjunctiva and sclera, thereby reducing IOP. The bloodstream then reabsorbs the aqueous humor.

Some patients require the placement of a glaucoma drainage device or tube shunt (eg, Ahmed, Molteno, Baerveldt). This device is adhered to the sclera between the rectus muscles, and a drainage tube is inserted into the anterior or posterior chamber through a tiny incision in the sclera. It allows the fluid to flow out from the interior of the eye, where it can be reabsorbed.

Recuperation from incisional surgery is generally short. An eye patch is usually worn for a few days after surgery. Activities that expose the eye to water (eg, showering, swimming) should be avoided. To avoid complications, refraining from heavy exercise, straining, or driving for a short time are recommended.


Viscocanalostomy was developed as an alternative to trabeculectomy. Although many viscocanalostomy techniques are available, the procedure involves production of superficial and deep scleral flaps, excision of the deep scleral flap to create a scleral reservoir, and unroofing of the Schlemm canal. A high-viscosity viscoelastic, such as sodium hyaluronate, is used to open the canal and create a passage from a scleral reservoir to the canal. The superficial scleral flap is then sutured to become watertight, trapping the viscoelastic until healing takes place. [36] According to one study, in terms of complete success and number of antiglaucomatous medications required postoperatively, IOP control appears to be better with trabeculectomy than with this procedure. [37] However, viscocanalostomy is associated with fewer early postoperative complications.

Shunt placement

The Ex-PRESS shunt is a 3-mm device that is inserted at the edge of the cornea. It is a microscopic conduit that drains excess fluid out of the eye and into the tissues that surround the eye. Standard glaucoma surgeries can take from 30 minutes to 1.5 hours, but surgery with this new shunt takes 10 minutes. According to one study, the incidence of complications after the implantation of an Ex-PRESS shunt directly under the conjunctiva was unacceptably high, despite a significant reduction in the IOP. [3]


Preoperative Details

Glaucoma surgery is generally performed as an outpatient procedure with the patient under local anesthesia with sedation. Before glaucoma surgery, the ophthalmic surgeon must evaluate the patient carefully to assess for concurrent ocular disease, neovascular glaucoma, uveitis, and/or conjunctival scarring, all of which guide an individualized surgical approach. The surgeon will discuss the specific condition, the details of the procedure to be performed, and the risks and the benefits of the procedure with the patient. The patient is required to sign an informed consent agreement before glaucoma surgery is performed.


Intraoperative Details

Multiple individualized considerations are taken into account during glaucoma surgery. Intraoperative application of mitomycin-C (MMC) or 5-fluorouracil (5-FU) may also be considered by the surgeon for prevention of filtration fibrosis and failure. It is important to note the patient’s other concurrent ocular conditions, if any, because 5-FU is toxic to the corneal epithelium, and both 5-FU and MMC have been associated with hypotony maculopathy from bleb leaks and an increased risk for endophthalmitis. Extreme caution must be taken when applying these agents to the filtration site during glaucoma surgery.


Postoperative Details

Postoperative appointments are scheduled for the day after the surgery and for several weeks thereafter. Postoperative medications generally include an antibiotic drop, an anti-inflammatory drop, and a cycloplegic drop, which maintains pupil dilation and helps manage pain. Glaucoma drops may be continued at a level determined by the ophthalmologist if needed.



The postoperative period generally lasts 2 to 3 months. Most patients do well after surgery and find that surgery controls their glaucoma without the need for continued topical medications.

For excellent patient education resources, visit eMedicineHealth's Eye and Vision Center. Also, see eMedicineHealth's patient education articles Ocular Hypertension, Normal-Tension Glaucoma, Glaucoma FAQs, Glaucoma Medications, and Subconjunctival Hemorrhage (Bleeding in Eye).



Complications of glaucoma filtration surgery include the following:

  • Intraoperative and postoperative suprachoroidal hemorrhage [38]
  • Hypotony
  • A flat anterior chamber and elevated or normal intraocular pressure (IOP), which includes suprachoroidal hemorrhage, aqueous misdirection, and pupillary block
  • Visual loss
  • Intraoperative complications of filtration procedures (eg, conjunctival buttonholes and tears, scleral flap disinsertion, and vitreous loss)
  • Postoperative complications of filtration procedures (eg, bleb leaks, early and late failure of filtering blebs, encapsulated blebs, symptomatic blebs, cataract formation, and bleb-related ocular infection)

Each of these complications is discussed below.

Intraoperative and postoperative suprachoroidal hemorrhage

Suprachoroidal hemorrhage is a serious complication that can be seen during or after any intraocular surgery. If it occurs intraoperatively and cannot be controlled (ie, expulsive hemorrhage), it can lead to loss of vision. The incidence of this complication in the general population after cataract extraction is approximately 0.2%. The incidence of a suprachoroidal hemorrhage in patients with glaucoma who undergo various types of intraocular surgery is reportedly 0.73%.

Ocular risk factors for a suprachoroidal hemorrhage are glaucoma, aphakia, pseudophakia, previous vitrectomy, vitrectomy at the time of glaucoma surgery, myopia, and postoperative hypotony. Systemic risk factors are arteriosclerosis, high blood pressure, tachycardia, and bleeding disorders. The source of the hemorrhage is usually one of the posterior ciliary arteries, particularly at the point of entrance of the short posterior ciliary vessels into the suprachoroidal space. Vascular necrosis seems to be present with subsequent rupture of the vascular wall.

Intraoperative suprachoroidal hemorrhage can be associated with a sudden collapse of the anterior chamber and loss of the red reflex noted under the microscope. The patient may complain of sudden pain that breaks through local anesthesia. If the process is gradual, a dark mass that evolves slowly can be observed through the pupil; however, if the process is abrupt, the hemorrhage may be expulsive. If noticed intraoperatively, it is important to stop the procedure and to close any intraocular incisions with suture.

Postoperative suprachoroidal hemorrhage usually occurs within the first week after glaucoma surgery and is generally associated with postoperative hypotony. Typically, the development of a suprachoroidal hemorrhage is acute and associated with the sudden onset of severe pain.

Examination of the anterior segment frequently reveals a shallow anterior chamber and normal or high IOP. On the fundus examination, a detached and dark choroid is noted. The choroidal elevations have a dark, reddish brown color. Some patients present with bleeding into the vitreous cavity and, uncommonly, retinal detachment. Ultrasonography can be used to aid in the diagnosis of a suprachoroidal hemorrhage when a fundus examination is not possible. Control of hypotony with referral to a retinal specialist for evaluation is important in the setting of suprachoroidal hemorrhage. [38]


Hyphema is a common postoperative occurrence in glaucomatous eyes after filtration surgery and surgical peripheral iridectomy. Bleeding commonly arises from the ciliary body or cut ends of the Schlemm canal, although it might arise from the corneoscleral incision or the iris.

Hyphema generally occurs during surgery or within the first 2 to 3 days after surgery. Intraoperatively, if a bleeding spot does not stop spontaneously, it must be identified and coagulated. During filtration surgery, performing the internal sclerostomy as far anteriorly as possible decreases the risk of bleeding.

In most cases, no treatment is necessary, and the blood is absorbed within a brief period of time. Cycloplegics, corticosteroids, restriction of activity, and elevation of the head of the bed 30° to 45° (to prevent blood from obstructing a superior sclerostomy) are recommended. Increased IOP can occur, particularly if the filtering site is obstructed by a blood clot; if necessary, it should be treated with aqueous suppressants. Injection of a tissue-plasminogen activator may be considered to break up the fibrin clot.

Surgical evacuation can be considered depending on the level of IOP, the size of hyphema, the severity of optic nerve damage, the likelihood of corneal blood staining, and the presence of sickle cell trait or sickle cell anemia (infarction of the optic nerve can occur at a relatively low IOP, and carbonic anhydrase inhibitors are contraindicated). Liquid blood can be easily removed with irrigation. If a clot has formed, it can be removed by expression with viscoelastic or with a vitrectomy instrument set at low vacuum. An example of hyphema is shown in the image below.

Hyphema. Deposition of RBCs in the anterior chambe Hyphema. Deposition of RBCs in the anterior chamber.


Hypotony, or IOP less than 6 mm Hg, after glaucoma surgery can result from excessive aqueous humor outflow related to excessive filtration, wound leak, or cyclodialysis cleft or from reduced aqueous humor production related to ciliochoroidal detachment, inflammation, inadvertent use of aqueous suppressants, or extensive cyclodestruction. These conditions can coexist; for example, low IOP due to overfiltration can induce ciliochoroidal detachment, which contributes to decreased production of aqueous humor.

Possible complications of hypotony include the following:

  • Flat anterior chamber
  • Gradual failure of the bleb
  • Visual loss
  • Cataract
  • Corneal edema
  • Descemet membrane folds
  • Choroidal hemorrhage
  • Hypotony maculopathy
  • Chorioretinal folds

According to Spaeth, the severity of a flat anterior chamber can be classified as follows: grade I, when peripheral-iris apposition is present; grade II, when pupillary border-corneal apposition is present; and grade III, when lens-corneal touch is present.

The depth of the central anterior chamber can be described relative to corneal thickness. Choroidal effusion occurs when fluid collects in the suprachoroidal space, resulting in forward movement of the lens-iris diaphragm with the anterior chamber becoming shallow. On fundus examination, moundlike elevations of the choroid, commonly in the periphery, are visible.

Flat anterior chamber and elevated or normal IOP

The following three conditions should be considered in patients with a postoperative flat anterior chamber and elevated or normal IOP: (1) suprachoroidal hemorrhage (see Intraoperative and postoperative suprachoroidal hemorrhage above), (2) aqueous misdirection, and (3) pupillary block.

Aqueous misdirection

Aqueous misdirection is also called malignant glaucoma or ciliary block glaucoma. It is characterized by a shallowing (flattening) of the anterior chamber without pupillary block (ie, in the presence of a patent iridectomy) or choroidal disease (ie, suprachoroidal hemorrhage) and commonly with an accompanying rise in IOP. Aqueous misdirection occurs in 2% to 4% of patients who have undergone surgery for angle-closure glaucoma, but it can occur after any type of incisional surgery. The chance of developing malignant glaucoma is greatest in phakic hyperopic (small) eyes with angle-closure glaucoma. In this condition, the aqueous humor is diverted posteriorly toward the vitreous cavity, increasing the vitreous volume and creating a forward pressure shallowing the anterior chamber.

Decompression and shallowing of the anterior chamber appear to be predisposing factors by inducing forward movement of the peripheral anterior hyaloid. Small choroidal effusions and a shallow anterior chamber sometimes occur before the episode of aqueous misdirection. The anterior hyaloid could be placed into direct apposition with portions of the secreting ciliary processes. Thus, the aqueous humor might move directly into the vitreous cavity. In hyperopic eyes (with a crowded middle segment), the peripheral anterior hyaloid in its normal position probably is close to the posterior ciliary body. In such eyes, cataract and filtration surgeries should be considered as high risk for aqueous misdirection.

In normal circumstances, the anterior hyaloid and the vitreous offer insignificant resistance to forward fluid flow. In some cases, pupillary block occurs first and is followed by aqueous misdirection. It is possible that a sudden onset of pupillary block forces the aqueous humor into the vitreous and expands the vitreous volume, with forward displacement of the peripheral hyaloid into direct apposition with the ciliary body.

Aqueous misdirection usually occurs in the early postoperative period after either filtration surgery or cataract surgery. The anterior chamber is shallow, and the IOP is high. However, with a functioning filtration bleb, the IOP may not be high. The peripheral iridectomy is patent, and a dilated examination and a B-scan ultrasonography confirm the absence of choroidal effusion or hemorrhage. If the adequacy of the surgical iridectomy is in doubt and pupillary block is possible, a laser iridotomy should be performed.

A trial of cycloplegics, aqueous humor suppressants, and hyperosmotic agents can be applied to reduce the volume of the vitreous cavity. On occasion, Argon laser therapy to shrink the ciliary processes may be required. If there is no response, Nd:Yag laser to the anterior hyaloid face or an anterior pars plana vitrectomy can be attempted.

Pupillary block

Pupillary block can be caused by adhesions between the iris and the lens, the pseudophakic lens, or the vitreous. The inability of the aqueous humor to pass from the posterior chamber to the anterior chamber results in the forward movement of the peripheral iris and closure of the drainage angle. Pupillary block typically occurs as a flat (shallow) anterior chamber with normal or elevated pressure. Distinguishing pupillary block from malignant glaucoma may be difficult. Although a peripheral iridectomy is intended at the time of filtration surgery, only the stroma of the iris is removed and the posterior pigment epithelium is left intact in a few patients. In these patients, blockage may develop. In other patients, the iris may become incarcerated in the wound or the iridectomy may be obstructed by intraocular tissue, such as the Descemet membrane, the anterior hyaloid surface, the vitreous (in aphakic eyes), or ciliary processes.

Therapy with cycloplegic-mydriatics may resolve pupillary block, but an Nd:YAG peripheral iridotomy should be performed. The anterior chamber readily deepens after an iridotomy is performed, although in the presence of localized compartments of blockage, multiple iridotomies are necessary. Usually, this deepening is associated with the sudden escape of aqueous humor through the iridectomy, confirming the diagnosis of pupillary block. If the laser iridotomy cannot be completed, a surgical iridectomy should be performed.

The development of a flat anterior chamber after glaucoma surgery is a relatively common complication. Therefore, the ophthalmic surgeon who performs intraocular glaucoma surgery should anticipate and be prepared to manage a postoperative flat anterior chamber.

A prolonged flat anterior chamber with hypotonia may result in serious consequences. According to a recent study, most eyes in which a flat anterior chamber with hypotonia developed after glaucoma surgery eventually acquired late cataract. This finding confirms a previous clinical impression that hypotonia is a cause of late cataract. When the anterior chamber is flat, contact can occur between the cornea and the lens. Contact between the corneal endothelium and the anterior lens capsule usually results in damage to the cornea. Corneal damage can be further aggravated by the elevated IOP caused by the development of peripheral anterior synechiae.

Without proper medical and surgical interventions, the eye with a persistent flat anterior chamber with hypotonia can acquire superimposed secondary glaucoma that is difficult to control. Fortunately, most flat anterior chambers with hypotonia and choroidal detachment after a filtering procedure may spontaneously reform. However, this reformation usually occurs at the expense of varying degrees of peripheral anterior synechiae, closure of the filtering fistula, and late cataract formation.

The flat anterior chamber with hypotonia can be with or without a detectable external wound leak. When the Seidel test result is positive, a wound leak can be easily ascertained. However, in many instances, the Seidel test result is negative with an undetectable wound leak, implying that a flat anterior chamber with hypotonia can occur in the absence of a detectable external wound leak.

Medical management of a postoperative flat anterior chamber

The first step in managing a postoperative flat anterior chamber with hypotonia is a trial of medical treatment.

Cycloplegic agents are known to decrease the vascular transudation by decreasing the vascular permeability. Cycloplegic agents also relax the ciliary muscle and, thus, the posterior movement of the lens-iris diaphragm. The mydriatic effect of cycloplegic agents is also beneficial in preventing posterior synechiae. The theoretic implication of an increase in the uveoscleral outflow of the aqueous humor by cycloplegic agents should be considered.

Hyperosmotic agents may increase the depth of the anterior chamber by decreasing vitreous volume and suprachoroidal fluid.

Carbonic anhydrase inhibitors decrease the aqueous humor production. Reduced aqueous humor formation diminishes flow through the filtering fistula, increasing the chance of closure of the fistula and reformation of the anterior chamber. However, the use of a carbonic anhydrase inhibitor may work against reformation of the anterior chamber by further decreasing the aqueous humor secretion that is already curtailed in an eye with a flat anterior chamber with hypotonia.

Topical and systemic steroids may be tried for their action of decreasing the transudation and in counteracting the portion of the aqueous humor hyposecretion that may be caused by inflammation. Steroids also reduce the incidence of posterior synechiae and peripheral anterior synechiae.

A firm application of an eye patch or a tamponade with contact lens or scleral shell may be beneficial. Conjunctival tamponade against the filtering corneoscleral fistula implements a decrease in filtration and a better chance of reformation of the anterior chamber.

Medical therapy is of little value in the presence of an external wound leak, necessitating surgical repair.

Many eyes reform on this regimen. However, with the exception of a wound leak closure, the practical value of each measure is not clear, aside from theoretic considerations. Medical therapy is considered a failure if the anterior chamber fails to form after 5-6 days. At this point, the ophthalmic surgeon is obligated to surgically reform the anterior chamber.

Surgical management of a postoperative flat anterior chamber

Posterior sclerotomy for drainage of ciliochoroidal detachment and reformation of the anterior chamber may be performed at a readily exposable scleral site over the ciliary body rather than over the choroid, 6 mm to 10 mm from the limbus.

Posterior sclerotomy and reformation of the anterior chamber may be performed either off site or on site. In the off-site technique, a partial-thickness incision is created through the peripheral cornea at a site off the filtering surgery. An attempt is made to reform the anterior chamber with air, which usually fails unless the fluid from the supraciliary space and the suprachoroidal space is drained. A posterior sclerotomy is performed to drain fluid from the supraciliary space, which is continuous with the suprachoroidal space.

The area of the sclera, 3 mm to 5 mm from the limbus and a meridian away from a rectus muscle, is cauterized using a wet-field cautery. Then, a full-thickness radial incision of the sclera, about 2 mm in length, is created, entering into the supraciliary space to drain the accumulated fluid. Enough fluid is drained so that the anterior chamber can be fully reformed with air. Even when a choroidal detachment cannot be detected on ophthalmoscopy, enough transudate is usually present in the supraciliary space.

A balanced salt solution instead of air was previously used to reform the anterior chamber. The use of air is preferred because there is a better chance of maintaining a fully formed chamber and less chance of having to repeatedly reform the anterior chamber. The peripheral corneal incision may or may not be closed with a suture. The conjunctival wound overlying the scleral incision is closed by suturing.

After surgery, a strong topical cycloplegic agent and steroid-antibiotic combination eye drops are applied to the eye. Topical phenylephrine hydrochloride is also used to prevent posterior synechiae and the rare possibility of pupillary block by the air.

Postsurgical preventive measures for a reformed flat anterior chamber

Even with the successful reformation of a flat anterior chamber after glaucoma surgery, the development of late cataract is often a problem. Precautionary measures (at least those of theoretic significance) appear important in the prevention of a flat anterior chamber after an intraocular procedure. One precautionary measure is to avoid both sudden and large magnitudes of globe decompression during intraocular surgery. Preoperatively, IOP is decreased to a low level by using topical and oral glaucoma medications. The globe is gradually decompressed by slowly letting out the aqueous humor. The ophthalmic surgeon should avoid external pressure and excessive trauma to the globe, especially after the eye is opened.

Preoperative recognition of eyes in which intraoperative ciliochoroidal detachment might develop, despite the usual preventive measures, is important. Eyes with elevated episcleral venous pressure are particularly predisposed to severe ciliochoroidal detachment. Elevated episcleral venous pressure may be idiopathic or familial, or it may be associated with Sturge-Weber syndrome, other causes of orbital and episcleral arteriovenous malformation or fistula, or superior vena cava syndrome. In these eyes, performing preventive posterior sclerotomy incisions at the time of an intraocular surgery may be indicated.

Adequate closure of the wound in filtering surgery is important. Closure of the scleral wound must be just right; that is, it must be tight enough to retain the air in the anterior chamber according to the air test. The air test involves introduction of air into the anterior chamber with a 30-gauge cannula connected to a syringe filled with air, positioned under the lamellar scleral flap or through a paracentesis tract. If the air stays in the anterior chamber without tendency to extrude, the closure of the lamellar scleral flap in trabeculectomy or the size of the corneoscleral wound in other filtering procedures is considered optimal. If any air tends to extrude, then the closure is inadequate. In this case, one or more interrupted sutures are placed for tighter closure of the lamellar scleral flap or partial closure of the filtration wound. Then, the conjunctival wound is closed to form a watertight seal. 

Visual loss

Unexplained loss of the central visual field "wipeout" after glaucoma surgery is rare. Older patients with advanced visual field defects affecting the central field with split fixation are at an increased risk. Early, undiagnosed postoperative spikes in IOP and severe postoperative hypotony are possible causes for wipeout. [39]


Intraoperative complications of filtration procedures

Conjunctival buttonholes and tears

Conjunctival buttonholes and tears can lead to failure of bleb formation and a flat anterior chamber. The usual cause of conjunctival buttonholes is penetration of the tissue by the tip of a sharp instrument (eg, needle, scissors, blade, teeth of the forceps). Buttonholes and tears are more likely to occur in patients with extensive conjunctival scarring.

To diagnose a buttonhole intraoperatively, the conjunctiva should be carefully examined at the end of the procedure by filling the anterior chamber and raising the filtering bleb. If recognized, the buttonhole should be closed during surgery. If it is located in the center of the conjunctival flap, a purse string closure is attempted, either internally on the undersurface of the conjunctiva or externally if the flap has been reapproximated.

When the conjunctival buttonhole or tear occurs at the limbus, it can be sutured directly to the cornea, which should be deepithelialized. A mattress suture or, if large, a running suture with 10-0 nylon can be used. When the buttonhole or tear occurs near the incised edge of a limbal-based conjunctival flap, the sutures used to close the conjunctival incision can be placed anterior to the tear.

Scleral flap disinsertion

A thin scleral flap can be torn or amputated from its base during the surgical procedure. If sclerostomy has not been performed, a new scleral flap should be dissected in a different area. If sclerostomy has been performed, reapproximation of the scleral flap can be attempted with sutures. If unsuccessful, additional tissue is needed to cover the sclerostomy. This tissue can be obtained by transferring a piece of the Tenon capsule or a flap of partial-thickness sclera from the area adjacent to the defect. Alternatively, donor sclera, fascia lata, or pericardium can be used to cover the defect.

Vitreous loss

Vitreous loss during glaucoma surgery is an uncommon complication, especially in phakic eyes. Predisposing conditions to vitreous loss include high myopia, previous intraocular surgery, trauma, aphakia, and lens subluxation. Loss of vitreous can be associated with such complications as corneal edema, epithelial downgrowth, uveitis, retinal detachment, cystoid macular edema, and endophthalmitis.

The vitreous can mechanically plug the sclerostomy, leading to filtration failure. The vitreous should be removed from the surgical site and the anterior chamber with a vitrectomy instrument, avoiding damage to the lens in phakic eyes. In the aphakic eye where the vitreous fills the anterior chamber, an anterior vitrectomy can be planned as part of the primary procedure. In phakic or pseudophakic eyes where the vitreous is in the anterior chamber, pars plana vitrectomy may be considered to adequately remove the vitreous from the posterior segment and to avoid lens subluxation and lens injury.

Postoperative complications of filtration procedures

Bleb leaks

Bleb leaks can occur early in the postoperative period or months to years after filtration surgery. An inadvertent buttonhole in the conjunctiva during a filtering procedure or a wound leak through the conjunctival incision can be responsible for an early bleb leak. Spontaneous late bleb leaks are more frequent in thin avascular blebs, which occur more often when antimetabolites are used in the filtering procedure and after full-thickness procedures.

The incidence of early and late bleb leaks is higher in trabeculectomies supplemented with antimetabolites than in nonsupplemented surgeries. Leakage of the filtering bleb can be associated with hypotony, a flat (shallow) anterior chamber, and choroidal detachment, and it may increase the chance of bleb infection and subsequent endophthalmitis. Early leaking can flatten the bleb, leading to subconjunctival-episcleral fibrosis, which jeopardizes a satisfactory long-term filtration.

Bleb leaks are detected with the Seidel test. The tear film is stained with fluorescein. A fluorescein strip is applied to the inferior tarsal conjunctiva or directly to the bleb. Without applying pressure, the eye is examined under cobalt blue illumination. If a leak is present, unstained aqueous humor flows into the tear film. If no spontaneous leakage is present, pressure may be gently applied to either the globe or the bleb while the area is examined.

Intraoperatively, limbal-based conjunctival flaps and partial-thickness scleral flaps have been associated with fewer bleb leaks. Various nonsurgical and surgical modalities can be used in the treatment of a bleb leak. For instance, in early and late bleb leaks, autologous fibrin tissue glue (AFTG) offers an alternative nonsurgical treatment to limiting the bleb leak. [40]

Early and late failure of filtering bleb

Failed blebs are associated with inadequate IOP control and impending or established obstruction of aqueous humor outflow. The causes of failed filtering operations are divided into intraocular, scleral, and extraocular factors. Extraocular changes account for most failures of external filtering operations. Early failure of filtering blebs is characterized by high IOP, a deep anterior chamber, and a low and hyperemic bleb. Failing blebs should be promptly recognized because if the obstruction is not relieved, permanent adhesions between the conjunctiva and the episclera can lead to closure of the fistula. A tight scleral flap and episcleral fibrosis are the most common causes of early bleb failure. Internal obstruction of the fistula by a blood clot, the vitreous, the iris, or an incompletely excised Descemet membrane is also possible.

To reduce postoperative subconjunctival fibrosis and to preserve bleb function, postoperative topical steroids are routinely used. The use of antifibrotic agents in filtering procedures is associated with a higher success rate but also with a higher complication rate (eg, wound leak, hypotony maculopathy, ocular infection).

Intraoperative application of 5-FU has been described to limit fibroblast scarring of the filtration site. Complications associated with using 5-FU include corneal and conjunctival epithelial toxicity, corneal ulcers, conjunctival wound leaks, subconjunctival hemorrhage, and inadvertent intraocular spread of 5-FU.

MMC is approximately 100 times more potent than 5-FU. Postoperative complications associated with overfiltration, hypotony maculopathy, bleb leak, and bleb-related ocular infections can also occur when MMC is used.

Digital ocular compression and focal compression can be used to temporarily improve the function of a nonfunctioning filtering bleb. Digital ocular compression can be applied to the inferior sclera or the cornea through the inferior eyelid or to the sclera posterior to the scleral flap through the superior eyelid. Focal compression is applied with a moistened cotton tip at the edge of the scleral flap. Because of potential complications, digital ocular compression is suitable for patients who are physically capable of performing it and who have had a beneficial response to the initial massage by the ophthalmic surgeon.

In the early postoperative period, laser suture lysis can enhance the filtration. Gonioscopy performed before the laser can confirm an open sclerostomy with no tissue or clot occluding its entrance. Specially designed lenses or equipment can be used. Examples are the Hoskins, Ritch, or Mandelkorn lenses; the central button edge of the Zeis and Sussman lenses; the Goldmann lens; glass rods; or glass pipettes.

After the suture is cut, if the bleb and IOP are unchanged, ocular massage or focal pressure can be applied. Usually, only one suture is cut at a time to avoid the possible complications of overfiltration. A hole in the conjunctiva may occur because of trauma from the contact lens or the thermal burn of the laser. If a subconjunctival hemorrhage occurs, suture lysis can be difficult. In these cases, a krypton red laser or a diode laser should be used because its wavelengths are absorbed less by blood. Some sutures have more influence in restricting the aqueous humor runoff than other sutures. These key sutures should be identified during surgery, and caution should be exercised when cutting them.

The timing of suture release is critical. Suture lysis is effective within the first 2 weeks after surgery without antimetabolites; later, fibrosis of the scleral flap may negate any beneficial effect of this procedure. If antimetabolites have been used at the time of surgery, suture lysis can be effective months after surgery.

Releasable sutures are as effective as laser suture lysis. The use of releasable sutures allows the ophthalmic surgeon to tightly close the scleral flap, knowing that the flow can be increased postoperatively. The externalized sutures are easily removed and are effective in cases of hemorrhagic conjunctiva or thickened Tenon capsule tissue, both of which make laser suture lysis difficult. Disadvantages of releasable sutures include additional intraoperative manipulation and postoperative discomfort from the externalized suture, corneal epithelial defects, and, possibly, increased risk of ocular infection.

In patients with an incarceration of iris or vitreous occluding the sclerostomy, an Nd:YAG laser internal revision can be tried. When the cause of filtration failure is a blood clot or a fibrinous clot occluding the sclerostomy, tissue plasminogen activator can be helpful. Recombinant tissue plasminogen activator is a serine protease with clot-specific fibrinolytic activity. It can be injected into the anterior chamber or subconjunctivally at a dose of 7 mg to 10 mg in 0.1 mL. It works rapidly, and, within 3 hours, the effect is usually apparent. Hyphema is the most frequent complication.

In addition, transconjunctival needling procedures can be attempted to restore aqueous flow.

Encapsulated blebs

Encapsulated blebs are localized, elevated, and tense filtering blebs with vascular engorgement of the overlying conjunctiva and a thick connective tissue. This type of bleb commonly appears within 2 to 4 weeks after surgery. Encapsulation of the filtering bleb is associated with a rise in IOP after an initial period of pressure control after glaucoma surgery. They can interfere with upper eyelid movement and tear film distribution, leading to corneal complications, such as dellen and astigmatism. Often, it is seen through the eyelid, simulating a lid mass.

The frequency of bleb encapsulation after trabeculectomies without antimetabolites is 8.3% to 28%. In trabeculectomies with postoperative 5-FU, the reported incidence is frequently higher. The frequency of encapsulated blebs after guarded filtering procedures is lower with mitomycin-C (MMC) than with 5-FU.

Predisposing factors may include male sex and the use of gloves with powder, as well as previous treatment with sympathomimetics, argon laser trabeculoplasty, and surgery involving the conjunctiva. The causes of encapsulation are not clearly identified, but inflammatory mediators are probably involved in their development. The long-term prognosis for IOP control in eyes that develop encapsulated bleb is relatively good.

Symptomatic blebs

Filtering blebs are usually asymptomatic. Some patients experience discomfort, which is most common with large nasal blebs extending onto the cornea. Tear film abnormalities with dellen formation and superficial punctate keratopathy may occur. Corneal astigmatism, visual field defects, and monocular diplopia have been described in patients in whom large filtering blebs migrated onto the cornea.

Artificial tears and ocular lubricants can be helpful, especially in patients with abnormal tear film. Several chemical and thermal methods have been used to shrink blebs. A temporary medial tarsorrhaphy can alleviate symptoms of a nasal bleb by shifting it superiorly. Large blebs that extend onto the cornea can be freed by blunt dissection. The corneal extension can be excised with a cut parallel to the limbus, usually with excellent results. Partial surgical excision and conjunctival flap reinforcement are usually helpful, though bleb failure is possible.

Ulrich and coworkers described three patients in whom full-thickness glaucoma filtering procedures were complicated by marked extension of the bleb over the cornea, with subsequent symptoms that required surgical intervention. [41] The surgical management in each case involved blunt dissection of the bleb from the cornea, with revision of the remaining portion of the bleb differing in each case according to the intraoperative findings. Light microscopic examination of one surgical specimen revealed a markedly attenuated epithelium covering hydropic corneal stroma. The authors postulate that the mechanism of formation involves aqueous humor dissection between corneal epithelium and stroma, leading to abnormal hydration of the superficial lamellae.

Cataract formation

Cataract formation and progression of preexisting cataract can occur after filtration procedures. The reported incidence is 2% to 53%. Lens opacification is the main cause of early visual loss after filtration surgery. Intraoperative lenticular trauma is possible and can be recognized shortly after surgery.

A postoperative flat anterior chamber with lens-corneal touch rapidly precipitates cataract formation. Other probable risk factors include age, presence of exfoliation, use of air to reform the anterior chamber, profound hypotony, use of miotics and topical steroids, and inflammation.

Cataract extraction can be associated with an impairment of the function of the filtering bleb. Phacoemulsification of the lens with a corneal incision induces less conjunctival inflammation than large scleral incisions, and, theoretically, it may be the best method to preserve bleb function. Postoperative subconjunctival injections of 5-FU can be considered. [42, 43] If IOP control is borderline, a combined cataract extraction and filtration procedure may be the best choice.

Bleb-related ocular infection

Ocular infections related to filtration procedures can occur months to years after the initial surgery. The incidence of bleb-related ocular infections after filtration procedures ranges from 0.06% to 13.2%. Inferior filtering blebs, the use of antifibrotic agents during filtration surgery, thin walled avascular blebs, contact lens use, chronic bleb leak, blepharitis, and conjunctivitis increase the probability of bleb-related ocular infections.

Bleb-related ocular infections can affect three compartments: the subconjunctival space, the anterior segment, and the vitreous cavity. The spread of infection usually proceeds in that order. Because the fluid within the bleb is continuous with the anterior chamber, the bleb may be considered an exteriorized portion of the anterior chamber. Therefore, an infection of the bleb affecting the subconjunctival space (blebitis) has the potential to rapidly spread posteriorly. The bacteria that cause bleb-related endophthalmitis certainly arise from the ocular flora. The most commonly involved organisms include Streptococcus species, Haemophilus influenzae, and Staphylococcus species.

Patients with bleb-related ocular infection usually present with ocular pain, blurred vision, tearing, redness, and discharge. Examination often reveals conjunctival and ciliary injection (most intense around the bleb edge); purulent discharge; variable intensity of periorbital chemosis; corneal edema; and anterior chamber reaction, including keratic precipitates and, in some cases, hypopyon. The bleb typically has a milky-white appearance with loss of clarity; a pseudohypopyon within the bleb can be observed. A positive result on the Seidel test is common. Some patients may have a substantial leak, hypotony, and even a flat anterior chamber. Alternatively, increased IOP is possible because of internal closure of the sclerostomy site with purulence and debris. Vitreous reaction is not evident in early cases of blebitis, but, if untreated, the infection spreads to the posterior segment.

Bleb-related ocular infections have been classified into three different stages. In grade I, only bleb involvement is present. Erythema around the bleb and the milky-white appearance of the bleb with loss of clarity is observed. In grade II, the infection has extended into the anterior chamber, and cells and flare are noted. Hypopyon may be seen. In grade III, the vitreous is involved. If the media is not clear (ie, dense cataract), B-scan ultrasonography can be helpful to detect involvement of the retrolental area.

Complications of cyclodestructive procedures

The use of various forms of cyclodestructive procedures typically is restricted to eyes with recalcitrant and end-stage glaucoma because of the limited predictability. Some eyes require multiple treatments to achieve lower pressure, whereas other eyes become hypotonus or phthisical after a single session.

The cyclodestructive procedures that are currently used are cyclocryotherapy, noncontact Nd:YAG laser cyclophotocoagulation (CPC), contact Nd:YAG laser CPC, contact diode CPC, and endophotocoagulation. The latter techniques offer the potential of a more controlled destruction of the ciliary body processes and a lower incidence of complications compared with cyclocryoablation. For example, the 810-nm semiconductor diode laser possesses the theoretic advantages of good penetration and selective absorption by the pigmented tissues of the ciliary body. Endophotocoagulation offers the possibility of selectively treating the ciliary body epithelium with relative sparing of surrounding tissues.

Complications of cyclocryotherapy include severe pain, elevated IOP, hyphema (common in eyes with neovascular glaucoma), visual loss (wipeout fixation in patients with advanced optic nerve damage), choroidal detachment, retinal detachment, chronic hypotony, cystoid macular edema, anterior segment necrosis, vitreous hemorrhage, aqueous misdirection, cataract, lens subluxation, and phthisis. Pain often occurs during the first 2 days after cyclocryotherapy, and strong analgesics for pain control should be used. Laser cyclodestructive procedures do not usually result in as much pain.

A major concern after cyclodestructive procedures is the possibility of phthisis bulbi (0-7%). Phthisis bulbi is more common in patients with neovascular glaucoma and in patients who underwent cyclocryotherapy in four quadrants; it is least common after diode laser CPC. The possibility of sympathetic ophthalmia after cyclodestructive procedures is also a concern. Sympathetic ophthalmia has been reported after noncontact Nd:YAG laser CPC and contact Nd:YAG laser CPC.

Complications of cyclodialysis

Cyclodialysis is not a popular procedure because of its unpredictability. Some ophthalmologists still use it, especially in aphakic and pseudophakic glaucoma. After the procedure, miotics are used to maintain an open cleft; cycloplegics should be avoided. Cyclodialysis initially lowers the IOP by increasing uveoscleral outflow and then by decreasing the formation of aqueous humor.

Common complications of cyclodialysis are intraoperative bleeding and hyphema, which may limit its long-term success. Postoperative hypotony is associated with the accumulation of fluid between the ciliary body and the sclera. If the accumulation of fluid extends posteriorly, it may reach the macula, impairing visual acuity. The degree of hypotony is not related to the length of the cleft in the angle that is observed gonioscopically.

If visual function is compromised, cryotherapy can be used to partially close the cleft. Cryotherapy may be ineffective, or it may induce complete closure of the cleft and elevate IOP. Surgical closure of the cleft may be necessary. Spontaneous closure of the cleft may occur months after a successful surgery, producing an acute rise in IOP and pain resembling an attack of acute angle-closure glaucoma. In some cases, intensive miotic treatment associated with phenylephrine can reopen the cleft.

Other possible complications include corneal opacity, injury to the Descemet membrane, iridocyclitis, corectopia, lens subluxation, cataract, vitreous loss, vitreous hemorrhage, retinal detachment, and myopic refractive shift.

Complications of trabeculotomy and goniotomy

Trabeculotomy and goniotomy are the first surgical options in treating infants with glaucoma. Trabeculotomy is preferred when the cornea is so clouded that the angle cannot be properly visualized. UBM can be used to evaluate the anterior chamber angle before and after surgery in infants with glaucoma and corneal opacity. Trabeculotomy can be a useful option in treating some adults with glaucoma.

Intraoperative complications during trabeculotomy can be attributed to difficulty in identifying the Schlemm canal, which is more difficult to locate in infants than in adults. The initial goal is to open the outer wall of the Schlemm canal without perforating the inner wall into the anterior chamber. If penetration into the anterior chamber occurs, the iris may prolapse. In this case, iridectomy may be necessary.

If the subciliary space is incorrectly probed, forward rotation into the anterior chamber is not possible unless considerable force is exerted, causing cyclodialysis and iridodialysis. If the tip of the trabeculotomy probe is held toward the cornea during rotation, a tear in the Descemet membrane can occur, but it is usually small and does not cause corneal edema.

Severe complications after trabeculotomy and goniotomy are rare. Moderate bleeding into the anterior chamber is common. Blood clots are usually resorbed within a few days.

Complications of glaucoma drainage devices (tube shunts)

Tube shunts are useful when trabeculectomy with MMC has failed; in patients with active uveitis, neovascular glaucoma unresponsive to laser photocoagulation, inadequate conjunctiva, aphakia, or pseudophakia; and in and contact lens wearers. The drainage devices have been reported to increase the risk of conjunctival erosion overlying tube shunt or plate, disturbance of the extraocular muscles due to its location between the rectus muscles, corneal endothelial damage from direct tube contact, shunt occlusion by the iris or vitreous, and plate migration. 


Outcome and Prognosis

The goal of glaucoma-filtering surgery is to arrest the progression of the disease via a reduction in intraocular pressure (IOP). Glaucoma-filtering surgery is successful in maintaining normal IOP in approximately 80% to 85% of patients; the remaining patients require either addition of medical therapy or reoperation for adequate control.

The Advanced Glaucoma Intervention Study (AGIS) was conducted to examine the relationship between IOP and progression of visual field damage over 6 or more years of follow-up. [15] According to the investigators, "eyes with 100% of visits with IOP less than 18 mm Hg over 6 years had mean changes from baseline in visual field defect score close to zero during follow-up." Results of this study support evidence from earlier studies showing the protective role of low IOP in limiting visual field deterioration.

The outcome of surgery is improved if the operation is undertaken before the increased IOP causes serious damage to the optic nerve fibers. The prognosis is poor if the surgery is performed in the late stages of this disease.


Future and Controversies

The current practice of filtration surgery, especially with the use of antifibrotic agents, creates risks for conjunctival leaks, infections, and problems due to filtration blebs. Nonpenetrating surgery may avoid these problems but is subject to long-term failures. Extensive investigational research is currently focused on providing minimally invasive glaucoma surgery (MIGS) approaches to control IOP in patients with mild to moderate glaucoma. Examples of MIGS procedures include the use of the trabectome, iStent, CyPass Micro Stent, XEN glaucoma implant, and the Hydrus microstent. Improvements in the surgical control of intraocular pressure (IOP) are expected in the future.


Long-Term Monitoring

Long-term follow-up in patients who have undergone glaucoma filtering procedures is imperative not only to monitor the IOP response but also to monitor for complications such as blebitis, endophthalmitis, and filtration failure, all of which can occur years after the original procedure.