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Shields > SECTION II - The Clinical Forms of Glaucoma >

12 - Pupillary Block Glaucomas

Authors: Allingham, R. Rand

Title: Shields Textbook of Glaucoma, 6th Edition Copyright ©2011 Lippincott Williams & Wilkins

> Table of Contents > SECTION II - The Clinical Forms of Glaucoma > 12 - Pupillary Block Glaucomas

12

Pupillary Block Glaucomas TERMINOLOGY

Primary versus Secondary Angle-Closure Glaucomas

Angle closure is characterized by apposition of the peripheral iris against the trabecular meshwork, resulting in obstruction of aqueous outflow (see Chapter 7). The term glaucoma is used if there is evidence of glaucomatous optic nerve damage. Traditionally, some forms of angle-closure glaucoma have been referred to as primary angle-closure glaucoma because the mechanisms of angle closure were not thought to be associated with other ocular or systemic abnormalities or because the mechanisms were not well understood. Conditions that have been included in this group are pupillary block glaucoma, plateau iris, and combined-mechanism glaucoma. Other forms of angle-closure glaucoma

have been called secondary angleclosure glaucoma because of associated ocular or systemic abnormalities or because of more apparent mechanisms of angle closure, such as contracting membranes or inflammatory precipitates that pull the angle closed or space-occupying lesions that push it closed. As continued research has expanded our knowledge of the associated abnormalities and mechanisms of primary angle-closure glaucomas, the distinction between the primary and secondary forms has become increasingly artificial, and the concept should probably be abandoned.

One example of how increased knowledge has progressively blurred the distinction between primary and secondary glaucomas is seen in the condition called plateau iris (1, 2 and 3). This condition has traditionally been included with the primary angle-closure glaucomas. However, because of information regarding the mechanism of plateau iris, it is now considered to belong with the glaucomas associated with disorders of the iris and ciliary body (see Chapter 17).

Figure 12.1 Pupillary block glaucoma. A functional block between the lens and iris (A) leads to increased pressure in the posterior chamber (arrows) with forward shift of the peripheral iris and closure of the anterior chamber angle (B).

In this chapter, we consider several forms of glaucoma that share the common mechanism of pupillary block and that have traditionally been grouped as primary angle-closure glaucomas. The conditions that have been called secondary angleclosure glaucomas are considered in subsequent chapters in this section.

Pupillary Block Glaucoma

Pupillary block glaucoma is the most common form of angleclosure glaucoma. The initiating event is thought to result from increased resistance to flow of aqueous humor between the pupillary portion of the iris and the anterior lens surface (4), which is associated with mid-dilatation of the pupil (5). The functional block produces increased fluid pressure in the posterior chamber, causing a forward shift of the iris. Anterior movement of the peripheral iris can result in closure of the anterior chamber angle (4, 5 and 6) (Fig. 12.1). Four forms of pupillary block glaucoma may be distinguished on the basis of symptoms and clinical findings (7): acute angle-closure glaucoma, subacute angle-closure glaucoma,

chronic angle-closure glaucoma, and combined-mechanism glaucoma. Acute Angle-Closure Glaucoma

In acute angle-closure glaucoma, the symptoms are sudden and severe, with marked pain, blurred vision, and a red eye. The patient may also have nausea and vomiting.

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Subacute Angle-Closure Glaucoma

Subacute angle-closure glaucoma is thought to have the same pupillary block mechanism as the acute form, but symptoms are mild or absent (8). The condition has also been called intermittent, prodromal, or subclinical (9). Patients with subacute angle-closure glaucoma may have repeated subacute or subclinical attacks before finally having an acute attack or developing peripheral anterior synechiae with chronic pressure elevation (8).

Chronic Angle-Closure Glaucoma

In chronic angle-closure glaucoma, portions of the anterior chamber angle are permanently closed by peripheral anterior synechiae, and the intraocular pressure (IOP) is chronically elevated (9, 10). The synechial closure may result from a prolonged acute attack or repeated subacute attacks of angle-closure glaucoma. A variation of this condition has been called shortening of the angle or creeping angle-closure glaucoma (11, 12). It is important to look carefully for evidence of exfoliation syndrome, because exfoliation can predispose to pupillary block in some patient populations (see Chapter 15). Combined-Mechanism Glaucoma

In some eyes, the glaucoma appears to have open-angle and angle-closure mechanisms. The diagnosis is usually made after an acute angle-closure glaucoma attack in which the IOP remains elevated after a peripheral iridotomy, despite an open, normal-appearing angle.

EPIDEMIOLOGY

In most populations, pupillary block glaucoma is considerably less common than chronic open-angle glaucoma. However, there is a reversal in the ratio of angle-closure and open-angle glaucoma cases among Canadian, Alaskan, and Greenland Eskimos, with the former disorder occurring in approximately 0.5% of the general population and in 2% to 3% of those older than 40 years of age, with a predilection for women (13, 14, 15 and 16). A similar observation was made in population studies from China, Singapore, Mongolia, and South India and a mixed ethnic group in South Africa, in which the prevalence of angleclosure glaucoma was 2.3%, compared with 1.5% for chronic open-angle glaucoma (17, 18, 19 and 20). This prevalence of angle-closure glaucoma may be caused by a smaller corneal diameter and anterior chamber depth and a thicker, more anteriorly placed lens in affected individuals (21, 22 and 23). A study among Alaskan Eskimos also showed a rapid increase in hyperopia after age 50, reaching 71.5% in persons older than 80 years (24).

Studies of the anterior chamber angle in various populations provide an impression of the prevalence of those at increased risk for pupillary block glaucoma. In two large studies, 5% to 6% of those screened had suspicious anterior chamber angles, but only 0.64% to 1.1% were considered to have critically narrow angles (25, 26). In a Vietnamese population residing in the United States, 8.5% had critically narrow angles and were considered to be at high risk for occlusion (27).

Figure 12.2 Pupillary block glaucoma (A) contrasted with the plateau iris syndrome (B). In the latter situation, notice the relatively deeper central anterior chamber, the flat iris plane, patent iridectomy, and bunching up of peripheral iris in the anterior chamber angle.

CLINICAL FEATURES

The diagnosis of pupillary block glaucoma has several facets. During the course of every ocular examination, the physician must consider general risk factors in the medical history and look for anatomic features that may predispose to angle closure. The gold standard examination is gonioscopy, which is essential in identifying eyes with some form of angle closure or those at increased risk for angle-closure glaucoma (i.e., occludable angles). In other situations, the patient may present with signs and symptoms suggesting angle-closure glaucoma, and the correct diagnosis will depend on an understanding of the symptoms, predisposing circumstances, physical findings of the disease, and the differential diagnosis (Fig. 12.2). The various aspects of diagnosing potential or manifest pupillary block glaucoma are considered in this chapter.

Risk Factors

General Features of Patients

Several factors influence the configuration of the anterior chamber angle and the risk for pupillary block glaucoma.

Age

The depth and volume of the anterior chamber diminish with age (28), which may result from thickening and forward displacement of the lens (29, 30). Consequently, the percentage of individuals with critically narrow angles is higher in older agegroups. The prevalence of pupillary block glaucoma also increases with age, although it may peak earlier in life, compared with chronic open-angle glaucoma. One study found a bimodal pattern, with the first peak at ages 53 to 58 years and the second at 63 to 70 years (29). However, it can occur at any age, including rare cases in childhood (31).

Race

The relative prevalence of pupillary block glaucoma among all the glaucomas is increased in various populations of Inuit and

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individuals with Far Eastern Asian extraction (13, 14, 15, 16, 17 and 18). Acute angle-closure glaucoma is less common among blacks, but subacute or chronic angle-closure glaucoma is not uncommon and appears to be a regularly missed diagnosis (32, 33 and 34). The explanation for this difference is

uncertain. One study suggested that it might be caused by a thinner average lens thickness (33), although another investigation revealed the anterior chamber depth in Nigerian blacks to be equivalent to that of whites (35). The weaker response to mydriatics observed among African blacks could indicate that darker irides are less able to exert the force that may lead to acute pupillary block (36). Angle-closure glaucoma also has a reduced prevalence among American Indians and is often caused by a swollen lens when it does occur in this group (34).

Sex

There is a statistically significant predominance of females in populations with pupillary block glaucoma, which is probably because of the shallower anterior chamber among women in general (13, 14, 16, 28).

Refractive Error

The depth and volume of the anterior chamber are related to the degree of ametropia, with smaller dimensions occurring in those with hyperopia (28). However, the presence of myopia does not eliminate the possibility of angle-closure glaucoma because rare cases have been reported in such patients (37), possibly indicting a spherical or anteriorly displaced lens or an increase in corneal curvature (38). Family History

The potential for pupillary block glaucoma is generally believed to be inherited (see Chapter 8). In one study, 20% of 95 relatives of patients with angle-closure glaucoma were thought to have potentially occludable angles (39). However, aside from a few reported families in which many members developed angleclosure glaucoma, the family history is not very useful in predicting a future angle-closure attack (40).

Systemic Disorders

Researchers in one study found an inverse correlation between type 2 diabetes or an abnormal result on a glucose tolerance test and the anterior chamber depth (41). The same investigators also suggested that angle-closure glaucoma may be associated with an increased prevalence of denervation supersensitivity to autonomic agonists (42).

Findings on Routine Examination

Certain observations during the course of a routine ocular examination can help to establish the potential for angle closure.

Intraocular Pressure

Unless the patient has angle closure at the time of the examination, the IOP is usually normal. One study, however, found a larger-than-normal amplitude in the diurnal IOP curve, which the investigators thought might have prognostic value (43). Tonography also characteristically reveals normal outflow facility before or between attacks, unless peripheral anterior synechiae are present (5).

Evaluation of Peripheral Anterior Chamber

Photogrammetric studies of all forms of angle-closure glaucoma have revealed anterior chamber depths, volumes, and diameters that are smaller than those of matched controls (44). Anterior chamber depth and volume have also been shown to have diurnal variation, with lower values in the evening (45), although a correlation between diurnal variations of chamber depth and IOP is not clear. In any case, the most important step in the diagnosis of potential or manifest angle-closure glaucoma is to evaluate the anterior chamber depth and especially the configuration of the anterior chamber angle. Although this is best accomplished by gonioscopy, there are preliminary screening measures that may be useful in some situations and techniques of quantifying the anterior chamber depth.

Penlight Examination

When a slitlamp and goniolens are not available, the anterior chamber depth can be estimated with oblique penlight illumination across the surface of the iris. With the light coming from the temporal side of the eye, a relatively flat iris is illuminated on the temporal and nasal sides of the pupil, whereas an iris that is bowed forward has a shadow on the nasal side (46) (Fig. 12.3).

Slitlamp Examination

The central anterior chamber depth may be estimated during examination with the slitlamp, and several techniques for quantitating this parameter have been proposed (47, 48 and 49). However, the central

anterior chamber depth only weakly correlates with the angle width (50), and the parameter of greater diagnostic value in the context of angle-closure glaucoma is the peripheral anterior chamber depth. van Herick and colleagues (51) developed a technique for making this estimation with the slitlamp by comparing the peripheral anterior chamber depth to the thickness of the adjacent cornea (Figs. 12.4 and 12.5). This is commonly referred to as the van Herick technique. When the peripheral anterior chamber depth is less than one fourth of the corneal thickness, the anterior chamber angle may be potentially occludable.

Gonioscopy

When the peripheral anterior chamber depth is thought to be shallow (i.e., less than one fourth of the corneal thickness by van Herick slitlamp examination), careful gonioscopic examination of the angle is required. This is best accomplished with a Zeiss four-mirror lens or similar goniolens. A 180-or-more- degree closure of the angle (i.e., trabecular meshwork is not visible) constitutes an occludable angle, and it is important to use compression gonioscopy to determine whether the closure is appositional or synechial. The patient should be examined in a dark room and with the use of a short, narrow slit-beam to avoid constricting the pupil and artifactually opening the angle. The examiner also should take care to avoid extra pressure on the cornea so that the angle does not deepen artifactually. If necessary, the goniomirror on the Goldmann three-mirror lens

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can be used to avoid artifactual deepening of the chamber angle. If the peripheral iris is prominent, or the iris is very convex and it is difficult to see angle structures, it is often helpful to have the patient look in the direction of the mirror being viewed so that a more accurate assessment of what angle structures are visible can be made.

Figure 12.3 Oblique flashlight illumination as a screening measure for estimating the anterior chamber depth. A: With a deep chamber, nearly the entire iris is illuminated. B: When the iris is bowed forward, only the proximal portion is illuminated, and a shadow is seen in the distal half.

Figure 12.4 The slitlamp technique of van Herick and colleagues (51) is used for estimating the depth of the peripheral anterior chamber (PAC) by comparing it with the adjacent corneal thickness (CT). The PAC here is about 1 CT.

visible angle structures (52). A: Root of the iris. B: Ciliary body band. C: Scleral spur. D: Trabecular meshwork. E: Schwalbe line.

Other investigators think that any single criterion cannot fully describe the anterior chamber angle. Becker (53) proposed combining an estimation of the anterior chamber angle width and the height of the iris insertion, whereas Spaeth (26) suggested an evaluation of three variables: angular width of the angle recess, configuration of the peripheral iris, and apparent insertion of the iris root (Fig. 12.8). Whatever system the clinician prefers to use to document the appearance of the anterior chamber angle, it is important to pay close attention to these three aspects of the angle. One study proposed a relatively simple method for measurement of the distance from the iris insertion to the Schwalbe line using a reticule based in the slitlamp ocular during gonioscopy (54). The investigators called this technique biometric gonioscopy and found that it correlated well with other measures of anterior chamber angle, showing a higher degree of interobserver reliability than conventional gonioscopy. Additional features of the angle should also be studied and documented, such as peripheral anterior synechiae and degrees or abnormalities in pigmentation. One study found that patients with narrow angles may have a

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predominance of trabecular meshwork pigmentation in the superior quadrant, rather than the more common inferior location, which the investigators thought might be caused by rubbing between the peripheral iris and the meshwork (55).

Figure 12.7 The Shaffer gonioscopic classification of the anterior chamber angle is based on the angular width of the angle recess (1). The angular width and clinical interpretation are given for each of the examples. A: Wide open (20 to 45 degrees): closure improbable. B: Moderately narrow (10 to 20 degrees): closure possible. C: Extremely narrow: closure possible. D: Partially or totally closed: closure present.