Primary Angle-Closure Glaucoma


Background

In the past, variable and sometimes conflicting terminology has been used to describe different forms of angle-closure glaucoma. The problem arose from the fact that terminology was developed prior to the advent of indentation gonioscopy and laser iridotomy, when the mechanisms of angle-closure glaucoma were poorly understood. [12]

In the era of surgical iridectomy, an attack of acute angle-closure glaucoma (AACG) could arise in an eye that had developed peripheral anterior synechiae (PAS) because of gradual angle closure prior to the development of the attack. Conversely, a prolonged acute attack or a series of subacute attacks could lead to progressive PAS formation. Patients undergoing surgical iridectomy were dilated routinely after surgery, and shallow anterior chambers were not uncommon. Patients undergoing surgical iridectomy for AACG who were dilated postoperatively and had shallow anterior chambers not infrequently formed PAS. [34Prolonged apposition or repeated subacute attacks lead to gradual PAS formation. These usually begin in the superior angle, which is narrower than the inferior angle, as pinpoint synechiae, reaching to the midtrabecular meshwork and gradually expanding in width. [5]

Primary angle-closure suspect (PACS) was defined as nonvisibility of the filtering trabecular meshwork for 180° or more in the absence of PAS with normal intraocular pressure (IOP). Primary angle closure (PAC) can be further classified as synechial or appositional. Primary (appositional) angle closure refers to an eye with raised IOP (>21 mm Hg) associated with obstructed filtering trabecular meshwork of more than 180° in the absence of PAS, disc damage, or field changes. On the other hand, primary (synechial) angle closure (PAC) refers to an eye in which portions of the anterior chamber angle are closed permanently by PAS with more than 180° of iridotrabecular contact with or without raised IOP. The term primary angle-closure glaucoma (PACG) is used to denote PAC eyes with glaucomatous optic nerve damage or visual field loss. [6]

Pathophysiology

Eyes with progressive PAS formation eventually may develop AACG when pupillary block results in closure of the remaining portions of the angle unaffected by PAS. However, many patients develop gradual angle closure, elevated IOP, and glaucomatous damage in the absence of symptoms. The presentation is similar to that of PACG, with progression of glaucomatous cupping and visual field loss. [7]

PAS also may form during an acute attack, remaining after iridotomy has opened the unaffected portions of the angle. These PAS are usually high and broad. When first observed at this stage, it is impossible to determine whether the PAS formed before or during the attack, or at both times.

In eyes with darker irides, a second mechanism of progressive angle closure is more common. The closure is circumferential and begins in the deepest portion of the angle. Closure occurs more evenly in all quadrants, so that the angle progressively becomes shallower. The appearance over time is of a progressively more anterior iris insertion. Lowe has termed this creeping angle closure. [8The PAS gradually creep up the ciliary face to the scleral spur and then to the trabecular meshwork.

Combined mechanism glaucoma

Combined mechanism glaucoma refers to situations in which both open-angle and angle-closure components are present. Most commonly, angle-closure glaucoma is treated successfully with iridotomy, eliminating all appositional closure, and IOP still remains elevated, with or without the presence of PAS of any extent.

Conversely, an eye with open-angle glaucoma may later develop angle closure, either because of the natural development of pupillary block or because of exacerbation by miotic therapy.

Exfoliation syndrome commonly predisposes to combined mechanism glaucoma. [9In this case, open-angle glaucoma can develop independently years after iridotomy for angle closure, with progressive blockage of the trabecular network. In all of these cases, the residual open-angle component is treated as open-angle glaucoma.

Mixed mechanism glaucoma

This term often is used interchangeably with combined mechanism glaucoma, but should not be, because it creates additional confusion. It is better to reserve this term to describe an eye with angle closure due to more than one contributory mechanism. When pupillary block is eliminated by iridotomy and the angle opens to a greater degree than before the iridotomy, an appositional closure remains on the basis of plateau iris, phacomorphic glaucoma, or malignant glaucoma, a mixed mechanism may be present.

Plateau iris

Plateau iris refers to an anatomic configuration in which the iris root angulates forward and then centrally. [101112The iris root often is short and inserted anteriorly on the ciliary face, so that the angle is shallow and narrow, with a sharp drop-off of the peripheral iris at the inner aspect of the angle. The iris surface is relatively flat and the anterior chamber is not unusually shallow.

When appositional angle closure develops in the presence of a patent iridotomy or iridectomy, either spontaneously or after pupillary dilation, in an eye with this anatomic configuration, plateau iris syndrome is present. [13Some patients may develop AACG. The risk of postoperative pupillary dilation after iridectomy or iridotomy frequently is realized.

Until recently, plateau iris syndrome was considered rare. Two subtypes have been differentiated. In the complete syndrome, which is rare, IOP rises when the angle closes with pupillary dilation. In the incomplete syndrome, IOP does not rise. The differentiating factor is the height of the plateau with respect to the angle structures. If the angle closes to the upper meshwork or Schwalbe line, IOP rises because aqueous outflow is blocked completely, whereas, if the angle closes partially, leaving the upper portion of the filtering meshwork open, aqueous humor can still exit the eye. This condition is far more common, and its detection is important; these patients can develop PAS up to years after a successful iridotomy produces what appears as a well-positioned angle.

Plateau iris occurs because large and/or anteriorly positioned ciliary processes hold the peripheral iris up against the trabecular meshwork. [1415Iris cysts also may cause a situation equivalent to plateau iris. When dynamic gonioscopy is performed in such an eye, the ciliary processes prevent posterior movement of the peripheral iris. As a result, a sinuous configuration results (ie, double hump sign), in which the iris follows the curvature of the lens, reaches its deepest point at the lens equator, and then rises again over the ciliary processes before dropping peripherally. Much more force is needed during gonioscopy to open the angle than in pupillary block because the ciliary processes must be displaced, and the angle does not open as widely. In a morphometric study of the ciliary sulcus, Orgul et al proposed that the displacement of the pars plicata from the peripheral iris to the iris root during embryogenesis may be incomplete in eyes of shorter axial length. [16]

Patients with plateau iris tend to be female, younger (30s-50s), and less hyperopic than those with relative pupillary block. They often have a family history of angle-closure glaucoma. Except in the rare younger patients (20s-30s), some element of pupillary block also is present. If plateau iris was not diagnosed before iridotomy and IOP is elevated postlaser, careful gonioscopy should be performed. If the angle is open, secondary damage to the trabecular meshwork or pigment liberation with dilation are the most likely causes. If the angle is closed, the differential diagnosis, besides plateau iris, should include malignant glaucoma, in which the anterior chamber is extremely shallow; PAS, which can be ruled out by dynamic gonioscopy; or incomplete iridectomy.

Miotic-induced angle-closure glaucoma

Prolonged miotic treatment in eyes with open-angle glaucoma and narrow angles may lead to pupillary block and angle-closure glaucoma. [17PACG has been seen to develop after several years of miotic therapy in eyes that initially had wide-open angles. In some eyes, zonular relaxation occurs more readily than in other eyes, so that anterior lens movement and an increase in axial lens thickness may facilitate pupillary block and angle closure.

In other eyes, little change in the lens occurs, but progressively increasing pressure in the posterior chamber gradually pushes the peripheral iris against the trabecular meshwork. It is believed that eyes with exfoliation syndrome are particularly prone to develop miotic-induced angle closure. In these eyes, the iris is thicker and stiffer than normal because of deposition of exfoliation material within the stroma. In addition, zonular weakness allows the lens to move forward, leading to pupillary block.

Less commonly, miotic therapy can have a pronounced effect on lens position and trigger malignant glaucoma. [181920Unequal anterior chamber depths, a progressive increase in myopia, or progressive shallowing of the anterior chamber are clues to the correct diagnosis.

Epidemiology

Frequency

Worldwide

The worldwide prevalence of PACG among persons aged 40 years and older was estimated to be 0.69% in 2010, as compared to 1.96% for primary open-angle glaucoma (POAG), with China having the highest prevalence of PACG, at 1.26%. The number of people with PACG in the world was estimated to be over 15 million in 2010 (compared with >44 million for POAG), with 47.5% of these patients in China. By 2020, the number of patients with PACG in the world may increase to over 21 million. [21]

Europe and  United States

The current evidence-based estimate of PACG prevalence in European-derived populations is suggested to be 130,000 people in the United Kingdom, 1.60 million people in Europe, and 581,000 people in the United States. Accounting for aging population structures, cases are predicted to increase by 19% in the United Kingdom, 9% in Europe, and 18% in the United States within the next decade. [22]

Asia

The overall pooled prevalence of PACG among adult Asians was 0.75%. Ethnicity-specific pooled prevalence estimates were 0.97% in the Middle East group, 0.66% in the Southeast Asia group, 0.46% in the India group, 1.10% in the China group, and 1.19% in the Japan group. [23]

Mortality/Morbidity

If IOP is not controlled, glaucomatous optic neuropathy and visual field loss may progress.

Race

The prevalence of PACG appears to be highest among Chinese (1.26% among those ≥40 years), according to a review of worldwide statistics. The prevalence of PACG in whites of European ancestry is around 0.25%. The prevalence of PACG appears to be lowest among Africans and people of Middle Eastern ancestry (0.16%). [21]

Among the subtypes of angle closure, creeping angle closure is uncommon in whites, but it is much more prevalent in Asians, in whom it ranks high as a cause of blindness. Black patients with angle closure also tend to have this form.

Sex

Patients with PACG and plateau iris tend to be female.

Age

Patients with PACG tend to be elderly, often with coexisting cataract or at least lens thickening.

Patients with plateau iris tend to be in their fourth to sixth decade of age.

Prognosis

The prognosis is favorable with control of the IOP. [24]

Factors associated with disease progression in PACG eyes include large IOP fluctuations [25 and a thin central corneal thickness. [26]

Patient Education

For excellent patient education resources, visit eMedicineHealth's Eye and Vision Center. Also, see eMedicineHealth's patient education articles Glaucoma OverviewGlaucoma FAQsGlaucoma Medications, and How to Instill Your Eyedrops.


History

Primary angle-closure glaucoma (PACG) is usually asymptomatic because of its slow onset, as opposed to acute angle-closure glaucoma (AACG), which presents with pain and nausea due to the rapid intraocular pressure (IOP) increase. However, patients with PACG may report transient eye pain, headache, and/or halo visualization.

Physical

Insertion of the iris at or anterior to the scleral spur is rare in young individuals, and, in many eyes with angle-closure glaucoma that have such an insertion, creeping angle closure is the underlying reason. It occurs in eyes with slightly deeper anterior chambers than are found in AACG. Gradual shortening of the angle in the presence of iris bombé brings the peripheral iris close to the external angle wall more anteriorly, narrowing the gap between the iris and the trabecular meshwork. Eventually, AACG may supervene, or PAS may permanently occlude the trabecular meshwork and lead to elevated IOP and glaucomatous damage.

The IOP in eyes with primary angle closure (PAC) may be normal or elevated. As peripheral anterior synechiae (PAS) formation progresses in the absence of intermittent attacks, IOP rises gradually as less and less functional meshwork becomes available. In eyes with intermittent attacks, IOP rises more rapidly relative to the extent of PAS formation caused by recurrent damage to the trabecular meshwork by the transient angle closure.

Other signs 

Blotches of pigment on the meshwork, particularly in the superior angle, or deposits of black pigment in the angle of a lightly pigmented iris are highly suggestive of previous appositional closure. If the angle opens, this deposited line of pigment shows the extent of previous angle closure and sometimes can be a helpful diagnostic feature.

The anterior chamber is quiet and usually deeper than in eyes with AACG.

The pupil is normal.

The gradual elevation of IOP does not result in corneal endothelial decompensation, and corneal edema is rare. The IOP is usually less than 40 mm Hg and does not reach the levels found in AACG. Symptoms are absent until the pressure rises high enough to affect the cornea or until extensive visual field damage has occurred. Although iridotomy will eliminate the pupillary block, IOP often remains elevated, and further medical treatment or surgery is required.

Causes

Causes of PACG include PAS formation, plateau iris, combined mechanism glaucoma, mixed mechanism glaucoma, and miotic-induced glaucoma.


Diagnostic Considerations

Glaucoma associated with shallow anterior chamber

Primary angle closure

Plateau iris syndrome

Relative pupillary block (most common)

Secondary angle closure

Choroidal hemorrhage (acute)

Ciliochoroidal effusion

Acquired immunodeficiency syndrome (AIDS)

Arteriovenous malformations

Inflammation

Nanophthalmos

Trauma

Tumor

Uveal effusion syndrome

Cystinosis

Drug-induced acute transitory myopia (eg, diuretics, sulfonamides)

Elevated episcleral venous pressure associated with arteriovenous fistula

Hemorrhagic retinal

Hyperglycemia (acute)

Inflammation

Iridocyclitis with posterior synechiae and iris bombé

Posterior scleritis

Intraocular tumor (posterior segment melanoma, metastatic carcinoma, retinoblastoma, medulloepithelioma)

Lens dislocation

Luetic interstitial keratitis

Maroteaux-Lamy syndrome (MPS VI)

Multiple cysts of the iris and ciliary body

Nanophthalmos

Persistent hyperplastic primary vitreous (PHPV)

Phakic pupillary block

Postoperative panretinal photocoagulation

Postoperative scleral buckle

Retinal dysplasia

Differential Diagnoses


Imaging Studies

Spectral-domain optical coherence tomography

In patients with glaucoma, analysis of serial retinal nerve fiber layer thickness (RNFL) maps generated with spectral-domain optical coherence tomography (OCT) can aid in the detection of RNFL progression. [27 

Other Tests

Intraocular pressure (IOP) assessment

Goldmann applanation tonometry remains the criterion standard.

The accuracy of the measurement may be affected by the central corneal thickness, so the measurement of the corneal thickness (usually via ultrasound pachymetry) is important.

Gonioscopy

Static and dynamic (indentation) gonioscopy is used to evaluate and document the extent, the nature (appositional versus synechial), and the cause of the angle closure.

Optic nerve head and RNFL assessments

Qualitative: Slit-lamp biomicroscopy examination using noncontact lenses (eg, 90-D lens) or contact lenses (eg, central lens in Goldmann 3-mirror lens); green filter (red-free light) may aid in the identification of RNFL thinning; fundus photography for documentation (stereoscopic or nonstereoscopic)

Quantitative: GDx VCC nerve fiber analyzer; Heidelberg retinal tomography (HRT); OCT

Visual fields  [28]

Threshold testing by automated perimetry

Special programs, such as SWAP, may help identify early visual field losses.

Further investigations to delineate the mechanism of angle closure

Ultrasound biomicroscopy examination [2930]

Anterior segment OCT (AS-OCT) [31]

Histologic Findings

Peripheral anterior synechiae (PAS) across chamber angle, pigment deposition in trabecular meshwork

Staging

There is no formal staging for primary angle-closure glaucoma (PACG), but grading systems (eg, Shaffer, Spaeth) exist to allow a more objective documentation of the openness of the drainage angle.


Medical Care

It is important to recognize early stages of appositional angle closure in the absence of peripheral anterior synechiae (PAS) and to recognize deep, circumferential angle closure.

Laser iridotomy is indicated for primary angle closure (PAC) and primary angle-closure glaucoma (PACG). Laser iridotomy involves the creation of a hole in the peripheral iris by laser. [3233The hole provides an alternative pathway for aqueous to flow from the posterior chamber into the anterior chamber, bypassing the pupil. Therefore, iridotomy eliminates pupillary block and prevents forward bowing of the iris as a result of the pressure difference between the two chambers. Iridotomy opens those areas of the angle not involved by PAS and prevents further synechial closure.

Miotic treatment may enhance the development of PACG in the absence of an iridotomy. When miotic-induced angle closure occurs, the approach to treatment should be determined by assessing the medications necessary to control the glaucoma. If a patient is taking dipivefrin, discontinuation may be enough to open the angle and allow the patient to remain on miotics, assuming that intraocular pressure (IOP) remains under control. If the patient has been treated with miotics alone, substitution of aqueous suppressants may suffice. If the patient requires miotics for IOP control, laser iridotomy is warranted.

If the angle remains appositionally closed or spontaneously occludable after laser iridotomy, argon laser peripheral iridoplasty (ALPI) is indicated to prevent progressive damage to the angle or further appositional and/or synechial closure of the angle. [34353637If, after iridoplasty, some of the angle still remains appositionally closed, low-dose pilocarpine, such as pilocarpine 2% at bedtime, often suffices to maintain the patency of the angle.

The level of IOP and the extent of glaucomatous damage determine the need for continued medical treatment after iridotomy. Treatment is similar to that of open-angle glaucoma. Repeated gonioscopy is necessary. The need for further surgery cannot be predicted from the level of initial IOP or the gonioscopic changes.

Argon laser trabeculoplasty (ALT) has been reported to be both successful and unsuccessful after iridotomy in combined-mechanism glaucoma; however, overall, it has been found to be reasonably successful. [3839Selective laser trabeculoplasty (SLT) delivers laser energy to pigmented cells in the trabecular meshwork avoiding thermal damage to adjacent cells. In a multicenter prospective study on PACG eyes with high IOP despite iridotomy but with at least 90° of gonioscopically visible pigmented trabecular meshwork, it has shown 20% or more IOP reduction in 54% of eyes at 6 months. The authors suggested selective laser trabeculoplasty to be a safe and effective method of reducing IOP in PACG in which there is a sufficient extent of visible trabecular meshwork. [40However, long-term therapeutic effectiveness of selective laser trabeculoplasty in PACG eyes will have to be determined. Possible side effects include reduced endothelial cell count, IOP spike, and persistent uveitis. [41]

If the pressure remains uncontrolled and glaucomatous damage develops, filtration surgery is indicated. An increased chance of developing malignant glaucoma is present following filtration surgery in patients who have had angle-closure glaucoma.

Surgical Care

The two main challenges in the management of PACG are, firstly, to prevent progression of the angle closure and, secondly, to prevent progression of the glaucomatous optic neuropathy by controlling IOP. Various surgical procedures have different roles in meeting these challenges.

The diminishing role of surgical iridectomy

To prevent progression of the angle closure, all eyes with angle closure or very narrow drainage angles should undergo iridectomy or iridotomy to eliminate pupillary block. Nowadays, laser iridotomy has largely succeeded surgical iridectomy, except in exceptional circumstances. [4243]

Laser iridotomy has many advantages over surgical iridectomy. Laser iridotomy is noninvasive, so there is no inherent risk of endophthalmitis and wound complications, such as wound leak. With sequential laser techniques, the wound edge of the iridotomy is well coagulated and the risk of hemorrhage from iris tissue is much reduced. The movement of fluid when the iris is penetrated is a good sign of iris penetration, and the chance of an incomplete iridotomy is minimal. Furthermore, as no ocular incision is required, there is no risk of further shallowing of the anterior chamber and causing iridocorneal adhesion and damage, PAS and permanent closed angle, or precipitating malignant glaucoma. Laser iridotomy can also be conveniently performed on an outpatient basis, and it does not require operating room facilities.

As laser equipment and expertise have become widely available, the role of surgical iridectomy in the management of angle-closure glaucoma is now limited to situations in which laser iridotomy is not possible or effective, for example, in patients with significant corneal opacity. The inability of patients to cooperate may also be a relative indication for surgical iridectomy, which can be performed under sedation or even general anesthesia. Severe anterior chamber inflammation may repeatedly occlude a laser iridotomy, while the relatively larger iridectomy created by surgery is much more likely to remain open under such circumstances.

Trabeculectomy

Trabeculectomy is effective for PACG. [4445464748Trabeculectomy has been shown to have an overall success rate of 68% in controlling IOP. However, compared to primary open-angle glaucoma (POAG), any aqueous-draining procedure in an eye with a shallow anterior chamber and a chronic closed angle poses the risk of further shallowing the anterior chamber or precipitating malignant glaucoma. Trabeculectomy in PACG is associated with a higher risk of filtration failure, shallow anterior chamber, and malignant glaucoma/aqueous misdirection. As the incidence of PACG increases with age, many patients with PACG have co-existing cataract. Trabeculectomy increases the rate of cataract progression, and a significant proportion of patients will soon need cataract extraction after trabeculectomy.

Furthermore, future cataract extraction may result in loss of the functioning filter. It has been reported that 30-100% of previously functioning blebs required antiglaucoma medications to control IOP after extracapsular cataract extraction (ECCE). Therefore, trabeculectomy alone is not the ideal surgical option in medically uncontrolled PACG.

In theory, adjunctive antimetabolite should be used with trabeculectomy when performed in eyes with a high risk of filtration failure or when a very low target pressure needs to be attained. However, the risk factors for filtration failure specific to angle-closure glaucoma and the target pressure in angle-closure glaucoma have not yet been clearly defined. Trabeculectomy is associated with various complications, both early and late, including bleb leaks and bleb-related infections. These risks are further increased by adjunctive antimetabolite.

Lens extraction—alone or in combination with trabeculectomy

Lens position and thickness both play important roles in the etiology of angle-closure glaucoma. [49Lens extraction significantly increases anterior chamber depth and width of the drainage angle. Lens extraction has been actively studied and reported in recent years in the treatment of PACG. The lens may narrow the angle by pushing the peripheral iris anteriorly, and this effect will be more marked if the lens is cataractous. Both traditional extracapsular cataract extraction and phacoemulsification have been reported to lower IOP in PACG. Phacoemulsification alone has also been shown to normalize IOP in PACG.

Hayashi has shown that the depth of the anterior chamber and the width of the drainage angle in eyes with angle-closure glaucoma increased significantly after cataract extraction and intraocular lens implantation, which may lead to the decrease in IOP seen in the postoperative period. It has been postulated that removal of a large cataractous lens from an eye with a crowded anterior segment may improve aqueous outflow. It has also been postulated that during phacoemulsification, the irrigating fluid flushes cellular debris from the trabecular meshwork, decreasing resistance to aqueous outflow.

A multicenter, randomized controlled clinical trial comparing lens extraction versus laser iridotomy in patients with newly diagnosed PAC or PACG is being conducted by The Effectiveness in Angle-closure Glaucoma of Lens Extraction (EAGLE) Study Group. [50This ongoing study is aimed at evaluating the effect of cataract extraction with regards to IOP, quality of life, and cost in angle-closure glaucoma at 3 years.

Randomized controlled surgical trials by Tham et al in Hong Kong directly compared cataract extraction alone by phacoemulsification against combined phaco-trabeculectomy in PACG eyes with coexisting cataract. Their first study focused on PACG eyes that were adequately controlled by glaucoma drugs before surgery, [51while their second study focused on PACG eyes that were medically uncontrolled. [52In both clinical scenarios, it was demonstrated that phacoemulsification alone could significantly reduce IOP, as well as the requirement for glaucoma drugs, for at least two years after surgery. Combined phacotrabeculectomy resulted in even greater IOP and drug reductions, but was associated with more complications and additional surgery to manage the complications. [53Based on these initial results, the authors concluded that in medically controlled PACG with cataract, phacoemulsification alone may be considered as an initial treatment. In PACG eyes with cataract, higher preoperative IOP and increased requirement for glaucoma drugs correlate with failure to control IOP after phacoemulsification or phacotrabeculectomy. In medically uncontrolled PACG with cataract, either phacoemulsification alone or combined phacotrabeculectomy may be considered, depending on patient factors. [51525354]

In situations where medically uncontrolled PACG coexisted with an optically clear lens, a third randomized controlled trial by Tham et al compared the outcomes of clear lens extraction by phacoemulsification versus trabeculectomy alone. [55In this study, both phacoemulsification and trabeculectomy reduced IOP by over 30% at 24 months after surgery. Phacoemulsification reduced the requirement for glaucoma drugs by 60% and trabeculectomy by 89% at 24 months after surgery. Trabeculectomy was associated with more complications. Compared to trabeculectomy, clear lens extraction resulted in a significant reduction in synechial angle closure and an increase in anterior chamber angle width and anterior chamber depth in PACG eyes without cataract. [56The authors concluded that, with available data, either surgery could be considered for medically uncontrolled PACG eyes without cataract, depending on patient factors.

One study suggested that the IOP-lowering effect of lens extraction may be less pronounced in PACG cases with PAS covering three fourths or more of the angle. Therefore, lens extraction alone may have a role in improving IOP control in PACG, especially in cases with less extensive PAS and when the IOP is not grossly out of control. Good long-term IOP control has been found following lens extraction for PACG, and lens extraction should be considered in patients with PACG, especially those with hyperopia or a thick and anteriorly vaulted lens. [57]

Goniosynechialysis with/without lens extraction

Goniosynechialysis (GSL) is a surgical technique performed to strip the PAS from the trabecular surface in the angle and provide aqueous renewed access to the trabecular meshwork. [585960In eyes with minimal PAS, trabeculectomy is preferred because trabecular function in these eyes is expected to be poor and a fistula procedure would be more appropriate. On the other hand, there may be spikes of raised IOP during and after the GSL procedure leading to loss of vision. GSL is more suitable for eyes with a minimal to moderate degree of neuronal damage.

In the past, ophthalmologists have tried to sweep open a closed angle without direct visualization. This often failed because accurate instrument placement could not be achieved. In 1984, Campbell and Vela introduced a technique using direct intraoperative visualization of the angle and anterior chamber deepening with viscoelastic agents. [61Visualization has been further improved with the use of the Swan-Jacob lens. This specially-designed lens has a handle attached to a small diameter prism so that it will not obstruct the spatula from entering the anterior chamber at the limbus. When PAS has been present for less than 1 year, the overall success rate in terms of IOP control is approximately 80%. Irreversible damage to the meshwork may occur in areas of synechial closure, with proliferation of iris or fibrous tissue into the intertrabecular space. This may explain why GSL appeared to be less effective in closed angle of longer duration.

In order for GSL to be effective, it must be performed before there is irreversible histological change in the meshwork. The mechanisms causing the angle closure should also be eliminated by performing peripheral iridotomy, laser peripheral iridoplasty, or lens extraction, either alone or in combination, to minimize the possibility of recurrent closure. Tanihara et al reported success in using GSL followed by argon laser peripheral iridoplasty. [62]

The most common complication of GSL is intraoperative hemorrhage. Other complications include iridodialysis, cyclodialysis, and lens damage.

Teekhasaenee and Ritch have reported success with phacoemulsification combined with GSL, and Lai et al were successful with combined phacoemulsification and limited GSL, followed by diode laser peripheral iridoplasty, for PACG. [63The authors demonstrated with ultrasound biomicroscopy that lens removal in PACG would only deepen the peripheral anterior chamber, without actually opening up the angle, while GSL opened up the angle and allowed aqueous access to the trabeculum.

Nevertheless, both lens extraction and GSL performed alone have been shown to lower the IOP, although the mechanisms are uncertain and may or may not be common to both procedures. Combining GSL with lens extraction has the advantages of noticeable visual improvement after surgery, and the combined IOP-lowering effect of the two procedures. Furthermore, removal of the lens may decrease the possibility of recurrent angle closure. It has been shown that eyes undergoing combined phacoemulsification with GSL have a greater reduction in circumferential iridotrabecular contact area than eyes undergoing phacoemulsification alone. [64A 2015 prospective study, however, demonstrated that IOP-lowering effects of phacoemulsification and GSL do not differ significantly from those of phacoemulsification alone in medically well-controlled PACG with cataract. [65]

Cyclodestructive procedures

In 1950, Bietti introduced cyclocryotherapy. A temperature of -80°C was applied with a cryoprobe to destroy the ciliary body epithelium, stroma, and vasculature. The clinical usefulness of cyclocryodestruction is limited by its complications, which include hypotony, phthisis, hyphema, choroidal detachment, and retinal detachment.

In the past 10 years, transscleral diode laser cyclophotocoagulation (TSCPC) using the G-probe is becoming more popular and is used to treat many different types of glaucoma. [6667The semiconductor diode laser emits light of wavelength 810 nm, near the infrared spectrum. It is transmitted through the sclera and absorbed by melanin. The success rates of cyclodestruction vary among the different procedures and the types of glaucoma. Diode TSCPC was reported effective in controlling IOP to less than 21 mm Hg in 70-81% of pediatric and adult refractory glaucoma. However, there has been no large-scale study on its efficacy in the treatment of PACG. Since it decreases IOP by destroying the ciliary epithelium and reducing aqueous production, it should, theoretically, be effective even in eyes with complete synechial closed angle closure.

In a recent study, adjunctive diode TSCPC was effective in lowering IOP in 4 cases of PACG that were uncontrolled despite a glaucoma aqueous tube shunt and multiple medications. In another study, diode TSCPC appeared to be an effective and safe primary surgical treatment of medically-uncontrolled PACG, with IOP-lowering effect persisting up to two years.

The efficacy and relative safety, the portability of the equipment, the ease of learning, and the short duration required for performing this technique make diode TSCPC a potential primary or secondary surgical procedure in the future treatment of PACG. However, TSCPC is associated with some rare but potentially serious complications, and these should be balanced against its many advantages. Potential complications include uveitis, pupillary distortion, conjunctival burns, hyphema, chronic hypotony, cystoid macular edema, retinal detachment, phthisis bulbi, and scleral perforations.

An alternative to TSCPC is endoscopic cyclophotocoagulation (ECP), which involves laser treatment of the ciliary processes under direct visualization and is most commonly performed in combination with lens extraction in refractory cases. Endoscopic laser allows a more precise application of laser to the targeted ciliary tissue. An animal study has also shown that TSCPC is associated with a more persistent poor perfusion of the ciliary processes and therefore a higher risk of hypotony and phthisis. [68In an earlier retrospective study, it was reported to be able to achieve an IOP of less than 21 mm Hg in 90% of refractory glaucoma, including PACG eyes. [69Although hypotony and phthisical change were not reported in this series, reported complications of ECP included uveitis, hyphema, cystoid macular edema, visual loss, choroidal detachment and malignant glaucoma.

A more recent randomized prospective study has tried to compare the safety between combined cataract surgery with ECP and combined cataract surgery with trabeculectomy. [70With a mean follow up period of 2 years, 30% of ECP eyes achieved an IOP of less than 19 mm Hg without medication and 52% with medication. The authors suggested that combined cataract surgery with ECP to be a reasonably safe and effective alternative surgical option.

Glaucoma implants in primary angle-closure glaucoma

The use of a glaucoma implant for difficult-to-treat glaucoma is not new. There is a wide variety of such glaucoma drainage devices, from the early Molteno implant to the currently popular valve-equipped variety, such as the Ahmed implant. Overall, the success rates for controlling IOP for complicated cases range from 70-90%. However, because it is technically more difficult than trabeculectomy, and potentially serious complications can occur, the use of a glaucoma implant for PACG has been mainly confined to those patients in whom one or more previous filtering procedures have failed.

Among the studies that included PACG, the proportion of patients with PACG ranged from 1.7-9%. Aside from the small number of patients, another major problem with these studies is that only two published the results of the subgroup with PACG. One had only a single non-Asian patient with angle-closure glaucoma, who ended up with no light perception at 6 months, while the other included 10 patients of unspecified race, 7 of whom had successful surgery.

A more recent randomized study evaluated non-valved tube shunt surgery against trabeculectomy in patients with glaucoma who had previously failed trabeculectomy and/or cataract extraction with intraocular lens implantation. In this study, there were 18 eyes with PACG, with 7 randomized to the implant group and 11 to the trabeculectomy group. In the former study, there were 15 eyes (23%) with the diagnosis of PACG, iridocorneal endotheliopathy, and juvenile open-angle glaucoma treated with the 350 mmBaerveldt glaucoma implant. The immediate-term failure rate in this subgroup was 47%, compared with 19% in the group with POAG. Although this study did not provide a subgroup analysis for patients with PACG, the 1-year results found a higher success rate in the tube group compared to the trabeculectomy group. These results suggest a possible expanded role for the use of implants in eyes with previous ocular surgery.

Consultations

Glaucoma specialist

Complications

Cataract can occur with steroid and laser treatment.

Prevention

The risk factors for the development of angle-closure glaucoma are listed below. Individuals with such risk factors may consider ophthalmological screening.

  • Female
  • Asian descent
  • Increasing age
  • Hypermetropia
  • Positive family history
  • Cataract

An eye with previous acute primary angle closure (PAC) has over 50% chance of developing primary angle-closure glaucoma (PACG), despite laser peripheral iridotomy. These patients should be regularly monitored. Preventive measures, such as laser peripheral iridoplasty or lens extraction, may be indicated to lower this risk.

The fellow eye in a patient with a previous episode of acute PAC (acute glaucoma) has a 50% chance of developing acute PAC in 5 years and should be screened for narrow angle by gonioscopy. Prophylactic laser peripheral iridotomy is often indicated in the fellow eye to prevent acute or progressive angle closure


Medication Summary

The first step in the management of primary angle-closure glaucoma (PACG) is often a surgical procedure to open up, as far as possible, those segments of the drainage angle that are appositionally closed or narrow. Options may include laser peripheral iridotomy, argon laser peripheral iridoplasty, and lens extraction, depending on the mechanism(s) of angle closure. Intraocular pressure (IOP) may, however, remain increased after these procedures, which may be the result of extensive residual synechial angle closure. IOP-lowering medications are indicated if a safe IOP level cannot be reached after angle-opening procedures. [71]

In the past, timolol and pilocarpine were extensively used in PACG. Recent studies have demonstrated the superior IOP-lowering efficacy of prostaglandin analogue monotherapy over these conventional drugs, and even some combination therapies, in PACG. The IOP-lowering effect of prostaglandin analogues does not appear to be related to the degree of angle closure or to the extent of peripheral anterior synechiae (PAS). Once-daily prostaglandin analogue regimes are generally well tolerated by patients with PACG. Prostaglandin analogues have become an important member in the medical arsenal against PACG. [72]

Miotic agents

Class Summary

These agents directly stimulate cholinergic receptors in the eye, decreasing resistance to aqueous humor outflow.

Pilocarpine ophthalmic (Isopto Carpine, Pilopine HS Gel)

Instillation frequency and concentration are determined by response. Individuals with heavily pigmented irides may require higher strengths.

If other glaucoma medication also is being used, at bedtime, use gtt at least 5 min before gel.

Patients may be maintained on pilocarpine as long as IOP is controlled and no deterioration in visual fields occurs.

Beta-adrenergic Blocker

Class Summary

Thought to decrease IOP by reducing aqueous formation; however, some studies observed increased outflow.

Timolol ophthalmic (Betimol, Istalol, Timoptic, Timoptic-XE, Tiimoptic Ocudose)

May reduce elevated and normal intraocular pressure (IOP), with or without glaucoma by inhibiting inflow. Available in various solutions and gels with varying recommended application frequency.

The brands Timoptic XE and Istalol are both administered once daily. However, Timoptic XE is a gel-forming solution while Istalol is an aqueous solution.

Prostaglandin, ophthalmic

Class Summary

Reduces IOP by increasing uveoscleral outflow.

Travoprost ophthalmic solution (Travatan Z)

Prostaglandin F2-alpha analog and selective FP prostanoid receptor agonist. Exact mechanism of action unknown but believed to reduce IOP by increasing uveoscleral outflow.

Latanoprost (Xalatan, Xelpros)

May decrease IOP by increasing outflow of aqueous humor.

Bimatoprost (Lumigan, Latisse)

Prostaglandin agonist that selectively mimics effects of naturally occurring substances, prostamides. Exact mechanism of action unknown but believed to reduce IOP by increasing outflow of aqueous humor through trabecular meshwork and uveoscleral routes. Used to reduce IOP in open-angle glaucoma or ocular hypertension.

Tafluprost (Zioptan)

Prostaglandin agonist that selectively mimics effects of naturally occurring substances, prostamides. Exact mechanism of action unknown but believed to reduce IOP by increasing outflow of aqueous humor through trabecular meshwork and uveoscleral routes. Used to reduce IOP in open-angle glaucoma or ocular hypertension.

Carbonic anhydrase inhibitor

Class Summary

Inhibits aqueous humor formation by inhibiting carbonic anhydrase 2 (CA-II).

Brinzolamide (Azopt)

Catalyzes reversible reaction involving hydration of carbon dioxide and dehydration of carbonic acid. May use concomitantly with other topical ophthalmic drug products to lower IOP. If more than one topical ophthalmic drug is being used, administer drugs at least 10 min apart.

Dorzolamide (Trusopt)

Reversible carbonic anhydrase inhibitor that may decrease aqueous humor secretion, causing a decrease in IOP. Presumably, it slows bicarbonate ion formation with subsequent reduction in sodium and fluid transport.

Systemic absorption can affect carbonic anhydrase in the kidney, reducing hydrogen ion secretion at renal tubule, and increasing renal excretion of sodium, potassium bicarbonate, and water.

Used concomitantly with other topical ophthalmic drug products to lower IOP. If more than one ophthalmic drug is being used, administer the drugs at least 10 min apart.

Acetazolamide (Diamox Sequels)

Reduces rate of aqueous humor formation by direct inhibition of enzyme carbonic anhydrase (CA) on secretory ciliary epithelium, causing in turn a reduction in intraocular pressure (IOP). More than 90% of CA must be inhibited before IOP reduction can occur. May reduce IOP by 40-60%. Effects are seen in about an hour, they peak in 4 h, and trough in about 12 h. Derived chemically from sulfa drugs. If one form is not well tolerated, another form may be better or lower dose of the drug may be better tolerated.

Used for adjunctive treatment of chronic simple (open-angle) glaucoma and secondary glaucoma and preoperatively in acute angle-closure glaucoma when delay of surgery desired to lower IOP

Alpha2-adrenergic agonist agent, ophthalmic

Class Summary

Reduces aqueous humor production and increases uveoscleral outflow.

Brimonidine (Alphagan P)

Relatively selective alpha2-adrenergic receptor agonist, decreases IOP by dual mechanisms. Reduces aqueous humor production and increases uveoscleral outflow. Has minimal effect on cardiovascular and pulmonary parameters. A moderate risk of allergic response to this drug exists. Caution should be used in individuals who have developed an allergy to Iopidine.

The brand Alphagan-P contains the preservative Purite and has been shown to be much better tolerated than its counterpart Alphagan.

Diuretic, Osmotic

Class Summary

These agents elevate glomerular filtrate osmolarity, resulting in decreased tubular reabsorption of water, thereby inducing diuresis.

Mannitol (Osmitrol)

Reduces elevated intraocular pressure when the pressure cannot be lowered by other means.

Initially assess for adequate renal function in adults by administering a test dose of 200 mg/kg, given IV over 3-5 min. Should produce a urine flow of at least 30-50 mL/h of urine over 2-3 h.

In children, assess for adequate renal function by administering a test dose of 200 mg/kg, given IV over 3-5 min. Should produce a urine flow of at least 1 mL/kg over 1-3 h.