Primary angle-closure glaucoma (ACG) affects an estimated 16 million people worldwide.1 Although ACG is only about one-third as prevalent as open angle glaucoma (OAG), the number of people blind from ACG is nearly equal to the number blind from OAG.2 Risk factors for ACG include old age, Asian or Inuit descent, hyperopia, and female gender.3,4 Due to the high prevalence of visual morbidity in ACG, the global public health burden it poses is substantial. Unfortunately, in Western nations, ACG is often misdiagnosed as OAG. The key to avoiding this pitfall is to use diagnostic gonioscopy and imaging techniques appropriately.

ANATOMY

Two main mechanisms are hypothesized to be responsible for angle closure: pupillary block and plateau iris. In the former, contact between the iris and the lens at the pupillary margin increases resistance to the flow of aqueous into the anterior chamber. When the pressure in the posterior chamber exceeds that in the anterior chamber, the iris—particularly the peripheral and midperipheral iris— moves forward and contacts the trabecular meshwork. Thus, there is aqueous blockage at two levels: the pupillary margin and the trabecular meshwork. Pupillary block is involved in the vast majority of cases of angle closure.

In plateau iris syndrome, the ciliary body is anteriorly positioned or rotated forward, resulting in the anterior displacement of the peripheral iris into the angle. The condition is characterized by either persistent angle closure or angle closure and elevated IOP upon pupillary dilation despite the presence of a patent iridotomy or iridectomy. Recent studies have shown that plateau iris, once thought to be a rare cause of angle closure, may be present in up to a third of cases of angle closure.5 Many of these eyes also possess an element of pupillary block.

CLASSIFICATION AND CLINICAL PRESENTATION

Angle-closure Nomenclature
A primary angle-closure suspect has a potentially “occludable” angle characterized by at least 180º of invisible posterior trabecular meshwork on gonioscopy without indentation.

Primary angle closure involves at least 180º of iridotrabecular contact and elevated IOP or the presence of synechiae. Closure of the angle may be caused by pupillary block, plateau iris, or a combination thereof.

The term primary ACG indicates primary angle closure in the presence of glaucomatous optic neuropathy.6

Acute Versus Chronic
Acute angle closure involves sudden and severe closure of the angle with very high IOP (often, 50-80 mm Hg), decreased visual acuity, corneal edema, pain, nausea, and vomiting. Even when the duration of extremely elevated IOP is short, rapid and significant damage can occur to the optic nerve, iris, and lens. Immediate intervention is therefore required.

Chronic angle closure, in contrast, is insidious. This form of the disease is more prevalent than acute primary angle closure and may cause more extensive glaucomatous damage. In a less subtle form, repeated episodes of relative pupillary block with subclinical attacks may produce intermittent symptoms of acutely elevated IOP and, over time, the development of peripheral anterior synechiae, at which point the presentation cannot be differentiated from more typical chronic angle closure.

Both acute and chronic angle closure frequently present and progress bilaterally but in an asymmetric fashion.

Secondary Versus Primary
ACG can occur secondary to other conditions such as anterior segment neovascularization, inflammation, developmental abnormalities, uveal effusion syndrome, or mass lesions that push the peripheral iris into the angle. Examples of these lesions include ring melanomas or iris and ciliary body cysts, iridocorneal endothelial syndrome, or retinopathy of prematurity. Secondary ACGs are pathologically different from and require alternative treatments than primary ACG.

HOW CLASSIFICATION WILL GUIDE TREATMENT

The treatment of angle closure has two goals: (1) to eliminate the mechanism of angle closure and (2) to control any persistent IOP elevation. An effective therapy should both control IOP and prevent further damage to the trabecular meshwork by eliminating apposition between the iris and the trabecular meshwork.

Laser Peripheral Iridotomy
Laser peripheral iridotomy (LPI) is considered the firstline treatment for primary angle closure (with or without glaucoma and with or without a component of plateau iris). Among the secondary causes of angle closure, LPI is only effective in the setting of pupillary block. During LPI, the surgeon uses an argon and/or Nd:YAG laser to create a hole in the peripheral iris, thus allowing aqueous to bypass the area of pupillary block. In cases of suspected angle closure, an LPI is often used as a prophylactic measure in an effort to prevent further progression of the angle closure. Studies, however, show that, despite a patent LPI, a large percentage of patients who actually have angle closure (as opposed to suspects) still require medication to control their IOP.7

Lens Extraction
If the patient has a coexisting cataract, lens extraction is the first-line treatment. This procedure not only removes the cataract, but it also relieves pupillary block by replacing the thick, convex crystalline lens with a thinner, artificial IOL. In addition, lens extraction may effectively treat plateau iris. Studies have shown that lens extraction opens the angle (to a greater degree than LPI), thereby improving anatomy.8 Also, patients who undergo lens extraction require fewer medications to control their IOP after surgery. 9 These advantages have led surgeons to perform lens extraction as a primary treatment for angle closure, but the use of this technique to treat angle-closure patients without coexisting cataract is controversial. Randomized clinical trials are needed to determine if lens extraction is a superior initial treatment for angle closure compared with LPI.

IMAGING

Although gonioscopy is the gold standard for assessing angle anatomy, the technique is subjective and difficult to reproduce. While it is unlikely gonioscopy will ever be completely replaced, several imaging techniques now available offer excellent reproducibility and quality in their detection of angle anatomy.

Ultrasound biomicroscopy (UBM) can image the anterior chamber and the ciliary body, and it can be used to diagnose plateau iris without the performance of an LPI. Because UBM is a contact technique and depends on the angle at which the technician holds the probe, however, quantitative measurements are not adequately reproducible for clinical use.

Anterior segment optical coherence tomography (AS-OCT) is also used to image the anterior chamber. Unlike UBM, this quick, noncontact technique does not require a highly skilled technician. Thus, AS-OCT could be used to screen patients for primary angle closure. Additionally, AS-OCT provides reproducible quantitative angle parameters. In the next few years, it is likely that eye care providers will be able to use AS-OCT to monitor the angle configuration and determine the most beneficial time for treatment as well as to distinguish primary angle closure from suspected primary angle closure more easily (Figure).

CONCLUSION

ACG represents a spectrum of disease, as does OAG. Both UBM and AS-OCT are very helpful in the diagnosis and clinical management of the angle-closure spectrum of disease, but properly performed gonioscopy remains essential.

Supported in part by National Eye Institute Vision Core Grant P30EY010608, a Challenge Grant to The University of Texas Medical School at Houston and an unrestricted grant to Northwestern University from Research to Prevent Blindness, and the Hermann Eye Fund.

Robert M. Feldman, MD, is the Richard S. Ruiz, MD distinguished university chair as well as professor and chairman of the Ruiz Department of Ophthalmology and Visual Science and the Robert Cizik Eye Clinic, The University of Texas Medical School at Houston. Dr. Feldman may be reached at (713) 559-5239; rfeldman@cizikeye.org.

Angelo P. Tanna, MD, is vice chairman and director of glaucoma service for the Department of Ophthalmology, Feinberg School of Medicine, Northwestern University, Chicago. Dr. Tanna may be reached at (312) 908-8152; atanna@northwestern.edu.

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