Pretutorial
Tutorial
Introduction
Pupillary Block Glaucoma
Epidemiology
Clinical Picture
Examination and Diagnosis
Provocative Testing
Treatment
Bibliography
Primary Angle-Closure Glaucoma
Bryan C. Hainline, MD
Worldwide, glaucoma is the second leading cause of blindness. Estimates have been made demonstrating that one-half of the 67 million people diagnosed with glaucoma have primary angle-closure glaucoma (PACG). In addition, the need to diagnose and treat glaucoma early in its progression is made manifest by the statistic that 6.7 million people globally have irreversible blindness secondary to glaucoma. In PACG, the iris obstructs the trabecular meshwork impairing subsequent outflow of aqueous humor. This obstruction of outflow in PACG exceeds that seen in primary open-angle glaucoma (POAG) such that the rise in intraocular pressure (IOP) can be acute in onset and substantial in intensity. PACG is differentiated from secondary angle-closure glaucoma as angle closure in PACG arises from mechanisms not associated with ocular or systemic abnormalities. Secondary angle-closure glaucoma is characterized by mechanisms associated with contracting membranes or inflammatory precipitates drawing the iris forward or forces pushing the iris from behind (such as tumors). PACG includes pupillary block glaucoma, plateau iris syndrome, and combined mechanism glaucoma. Pupillary block glaucoma is the most common subtype among the forms of PACG.
In pupillary block glaucoma, the angle closure is believed to stem from the pupillary portion of the iris coming into contact with the anterior lens surface and forming a functional or physical block to aqueous humor flow. It has been postulated that the musculature of the iris exerts a back pressure on the lens that subsequently increases the resistance of aqueous flow into the anterior chamber. Consequently, aqueous humor increases in volume in the posterior chamber causing the peripheral iris to bulge forward to physically occlude the trabecular meshwork. This bulge of the peripheral iris can be visualized with a slit lamp and is termed iris bombé (Slide 1).
The theory that POAG is more common than PACG does not apply to the Eskimos of Canada, Alaska, Greenland as well as populations in East Asia.
This relationship relates to the theory that East Asians and the Inuit Eskimos (Canada, Alaska, and Greenland) share the same genetic lineage of the Sino-Mongoloid race. Population-based surveys have revealed a 0.4% prevalence of PACG in white Americans, 2.6% to 5% in Inuit Eskimos, and 1.4% in Beijing Asians. The difference in prevalence observed in these races is commonly attributed to the shallow anterior chamber observed in the Inuit as compared to whites. In contrast, PACG is less common in black Americans, which has been attributed to thinner average lens thickness and generalized weaker response to mydriatics leading to a decreased force that the pupil is able to exert on the lens.
General risk factors for developing PACG include advanced age, female sex, hyperopia, family history, and diabetes. The elderly have been noted to have an increased incidence of PACG presumably due to anterior chamber size decrease secondary to increased crystalline lens thickness and decreased pupillary diameter. Women have been reported to have an increased incidence of PACG, which is similarly believed to arise from a shallower anterior chamber in women as compared to men. As decreased depth and volume of the anterior chamber correlate with the degree of hyperopia, an increased incidence of PACG is seen in hyperopic patients. In addition, a study has shown that 20% of 95 combined first- and second-degree relatives of patients with angle-closure glaucoma had potentially occludable angles. Positive correlations have been calculated that suggest that type II diabetes mellitus or abnormal glucose-tolerance tests relate to decreased anterior chamber depth.
Three different forms of pupillary block glaucoma have been described based on presenting symptoms and clinical findings.
Acute Angle-Closure Glaucoma
Patients with acute angle-closure glaucoma can appear markedly ill when they present. The patients may experience sudden severe
pain in a trigeminal nerve distribution, blurred vision, nausea, vomiting, bradycardia, and diaphoresis. The patient may also show an
extreme decrease in central visual acuity. Conjunctival hyperemia is present, which consists of a ciliary flush and congestion in the
conjunctiva. The cornea may be edematous and the pupil is typically irregular, vertically oval, in a mid-dilated position, and fixed.
This position of the pupil is believed to be due to ischemia and paralysis of the sphincter pupillae. As IOP increases, there is subsequent
decrease in perfusion to the sphincter muscle. Slit lamp examination may reveal a shallow anterior chamber, aqueous flare, pigment
dispersion, sector atrophy of the iris, and glaukomflecken in the anterior aspect of the lens. Acute angle-closure glaucoma is seen
most often with the mid-dilated pupil as lens-iris contact is greatest at this position of the pupil. This observation has been used to
explain why dimly lit areas, emotional stress, and pharmacological dilation can precipitate episodes of acute angle-closure glaucoma.
The rise in IOP can be dramatic, four- to five-fold, reaching values of 40 mm Hg to 60 mm Hg and higher in minutes (Slide 2).
Subacute Angle-Closure Glaucoma
Subacute angle-closure glaucoma is often viewed to have the same mechanism as seen in AACG, but corresponding symptoms
may be mild or absent. Patients may suffer from repeated subclinical episodes that precede an acute attack or predispose to chronic
angle-closure glaucoma. Patients with subacute angle-closure glaucoma typically have few clinical indicators suggesting an attack of
angle closure. Patients may experience episodes of blurred vision with a concurrent headache. Another symptom is the perception of
seeing colored haloes around lights during an episode. Physical signs are typically absent except for a narrow angle in subacute
angle-closure glaucoma.
Chronic Angle-Closure Glaucoma
Chronic angle-closure glaucoma is typified by closure of peripheral portions of the anterior chamber by synechiae that subsequently
produce chronic elevations in IOP. Patients with chronic angle-closure glaucoma typically have an asymptomatic clinical course similar
to that observed in patients with POAG and often present with glaucoma in an advanced state.
During a routine examination, IOP will be normal in these patients unless angle closure is present. Some researchers have suggested that a greater amplitude in the diurnal IOP curve may have prognostic significance. In addition, tonography has shown normal aqueous outflow preceding and between episodes, unless anterior synechiae are present.
In patients with PACG, anterior chamber depths, volumes, and diameters are decreased when compared to matched controls in photogrammetric studies. Estimating the anterior chamber depth and determining the anterior chamber angle structure are the most important diagnostic evaluations that must be performed in patients with PACG.
There are many ways to estimate anterior chamber depth including a penlight, slit lamp examination, and gonioscopic examination. When a slit lamp or a goniolens is not available, a penlight may be used to estimate anterior chamber depth. When shining a penlight at an oblique angle from the temporal side of the eye, a flat iris, with a corresponding deep anterior chamber, will illuminate on each side of the pupil. An iris that is bowed forward, suggesting decreased anterior chamber depth, will produce a shadow on the nasal side upon penlight illumination.
When estimating the peripheral anterior chamber depth with a slit lamp, van Herick’s technique may be used to maximize diagnostic significance based on the observation that central anterior chamber depth correlates poorly with factors involved in angle closure. Van Herick’s technique uses slit lamp observations of peripheral anterior chamber depth and adjacent corneal thickness (Slide 3).
Table 1. The Grading System for Van Herick’s Technique.
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The diagnostic criterion standard for an occludable anterior chamber angle is gonioscopy. Traditionally, when a slit lamp examination of peripheral anterior chamber depth reveals van Herick grade 1 or 2, a gonioscopic examination should be performed. Scheie’s grading system relies on the extent of anterior chamber structures that can be visualized.
Table 2. Scheie’s Gonioscopic Classification of the Anterior Chamber Angle
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Shaffer’s gonioscopic classification of the anterior chamber angle relies on the angular width of the angle recess.
Table 3. Shaffer’s Gonioscopic Classification of the Anterior Chamber Angle
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Spaeth suggested that factors such as angular width of the angle recess, configuration of the peripheral iris, and insertion of the iris root should factor into estimation of the extent of angle closure. Other examination findings of peripheral anterior synechiae and abnormalities in pigmentation of the superior trabecular meshwork also provide clinical evidence suggesting a potentially occludable or occluded angle.
Table 4. Spaeth’s Gonioscopic Classification of the Anterior Chamber Angle
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Generally, gonioscopic examination using any classification system preferred by a clinician must always observe the full width of the trabecular meshwork to the scleral spur to conclude that the angle is functionally open. Epstein points out that if only part of the trabecular meshwork is visualized by gonioscopy, the part not visualized may be blocked, in part, by iris apposition, and this block may be significant enough to produce functional closure (Slide 8 and Slide 9).
Alternative techniques, such as handheld and slit lamp ultrasound, have been investigated as potential screening tools for determining anterior chamber depth measurement in potentially occludable angles. Devereux and colleagues concluded that optical pachymetry outperformed handheld and slit lamp ultrasound in determining anterior chamber for depth. The study revealed optical pachymetry an 85% sensitivity and an 84% specificity, 83% sensitivity and 81% specificity for slit lamp ultrasound, and 86% sensitivity and 73% specificity for handheld ultrasound, all at a screening cutoff of less than 2.22 mm for detecting occludable angles. Although handheld ultrasound appears to be a possible method of screening in the field, the investigators remarked that the false-positive rate was too high to permit use as a screening device.
If a patient is determined to a have potentially occludable angle, some surgeons may perform provocative testing to identify patients for whom prophylactic surgery would prove beneficial. A mydriatic may be used (e.g., tropicamide 0.5%) and a corresponding rise in IOP of 8 mm Hg is deemed a positive test. A dark room test may be used that involves placing the patient in a dark room for 60 to 90 minutes, keeping the patient awake, and subsequently assessing IOP in a minimally lit room. A rise in IOP of 8 mm Hg is considered a positive test. Prone provocative testing may also be used, which involves placing the patient prone for 60 minutes, with a positive test being a rise in IOP of 8 mm Hg or more. Others have suggested that combining the dark room test with the prone test can achieve even higher sensitivity. Pilocarpine 2% and phenylephrine 10% can be applied at the same time for three successive applications to dilate the pupil to the midposition. This test has not been shown to have consistent sensitivities and specificities adequate for provocative use.
The issue of provocative testing is controversial with many surgeons concluding that all of these tests do not produce high enough sensitivity or specificity to alter clinical judgment. Many ophthalmologists consider an accurate history and physical examination the tools to achieve the greatest results when evaluating patients with a potentially occludable angle.
Acute angle-closure glaucoma is a medical emergency. The definitive treatment for pupillary block angle-closure glaucoma is surgery. However, many ophthalmologists consider it necessary to medically manage the acute attack before attempting surgical intervention. This is evident when in an acute attack of angle-closure with high IOP, corneal edema and diminished anterior chamber depth may make surgery difficult. IOP should be lowered to prevent damage to the optic nerve head.
Medical management typically revolves around decreasing IOP and relief of angle closure. In an attempt to decrease IOP, oral or topical carbonic anhydrase inhibitors, topical beta-blockers, and alpha-2 agonists may be used. In cases of resistance to these agents, a hyperosmotic agent such as mannitol may be used. Often, these patients are extremely sick; a patient’s nausea and vomiting may complicate oral medication attempts, and intravenous infusions of hyperosmotic solutions and carbonic anhydrase inhibitors should be used. Relief of angle closure may be attempted once the IOP has been lowered to permit adequate perfusion of the iris. A low dose of pilocarpine 1% to 2% may be sufficient to relieve an attack of angle closure and should be used in small amounts to prevent paradoxical worsening of the angle closure or cholinergic toxicity. Even though alpha-antagonists would appear to have a therapeutic role, drugs such as thymoxamine have not been proven to be effective in relieving acute attacks when used alone. A contraindication to therapy is the use of strong miotics, such as echothiophate, as these agents may exacerbate the relative pupillary block by the induced smaller position of the pupil and forward movement of the lens-iris diaphragm.
In addition, some practitioners have succeeded in abating an acute attack by pressing on the central cornea with an applicator and rotating the cornea and sclera to force aqueous flow from the central to the peripheral anterior chamber. Compression gonioscopy with a gonioprism may also achieve the same end result or, if necessary, surgical iridectomy. If the IOP remains elevated despite medical therapy, emergent laser iridotomy should be performed. If corneal edema is present, laser pupilloplasty or peripheral iridoplasty are options to halt the acute attack and clear the cornea.
In a case of decreased IOP in response to medical therapy, the patient should undergo a repeat gonioscopic exam to evaluate the mechanism of the lowered IOP. An anterior chamber angle that is open without the use of compression gonioscopy indicates that the acute attack has subsided and surgery is not necessarily urgent. Laser iridotomy may still be performed immediately even if inflammation is present. If the anterior chamber is closed during repeat gonioscopy, the IOP decrease must be assumed to be secondary to decreased aqueous production and not relief of the closed angle. In this scenario, laser iridotomy should be performed immediately to reopen the closed angle, assuming that permanent synechiae have not yet formed.
Laser iridotomy is the preferred treatment in pupillary block glaucoma. Patients undergoing laser iridotomy alone may require additional medication or even filtering surgery in the future. If patients suffer from a prolonged acute attack of angle closure or have suffered some subacute angle closure previously, the former additional therapies may be required. For example, if gonioscopy reveals partial synechial closure of the anterior chamber angle, laser iridotomy should be performed. If the IOP fails to decrease after iridotomy, medication or filtering surgery is indicated. Filtering surgery should be undertaken with great care, as malignant glaucoma is a complication observed in patients with angle-closure glaucoma.
After an acute attack of angle closure in one eye, it is generally recommended that a prophylactic peripheral iridotomy should be performed on the opposite eye. Acute attacks of angle closure in the opposite eye are typically seen in the first year after the first episode of angle closure. This indicates the necessity of performing prophylactic surgery after episodes of angle closure. Exceptions to this prophylaxis include conditions with deep anterior chambers such as anisometropia, pseudophakia, aphakia, and a dislocated lens.
Plateau Iris Syndrome
The plateau iris syndrome form of PACG is less common than pupillary block and is observed most commonly in young adults.
Plateau iris syndrome is caused by forward displacement of the ciliary body with corresponding ciliary processes, which hold the
peripheral iris in an anterior position overlying the trabecular meshwork. The iris is commonly located on the same plane as Schwalbe’s
line and a recess is present in the peripheral angle. In contrast to pupillary block glaucoma, maximal pupillary dilation in patients with
plateau iris syndrome results in maximal closure of the anterior chamber angle.
Patients with plateau iris syndrome are characteristically asymptomatic until they experience an attack of acute angle closure or develop chronic angle closure. Patients with plateau iris syndrome demonstrate deep axial anterior chambers but narrow peripheral anterior chambers when examined with a slit lamp. This disparity between axial and peripheral anterior chamber depth is a diagnostic clue that plateau iris syndrome is present. On gonioscopic examination, the iris is flat instead of convex with a corresponding narrow anterior chamber angle. If indentation gonioscopy is used, the trabecular meshwork is visible with a sine wave appearance of the peripheral iris due to the iris hanging over the anterior ciliary processes.
Most cases of suspected plateau iris syndrome have at least some component of pupillary block and patients are treated with peripheral iridotomy. Plateau iris configuration occurs when the typical iris configuration is present but without angle closure. To definitively diagnose plateau iris syndrome, a peripheral iridotomy must be performed; an anterior chamber angle that remains occludable confirms plateau iris syndrome. A provocative pupillary dilation trial may be used next to confirm the diagnosis. If the diagnosis of plateau iris syndrome is confirmed, argon laser iridoplasty may be used to shrink the peripheral iris and relieve the closed angle
Combined Mechanism Glaucoma
A small subset of patients have glaucoma that has both open-angle and closed-angle components. This diagnosis is typically made
in a patient who experienced an acute attack of angle closure that was treated with a peripheral iridotomy. In these patients, IOP
remains elevated despite the presence of an open angle. Ensuing treatment is aimed at the open-angle component of the patient’s glaucoma.
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