Ординатура / Офтальмология / Английские материалы / Clinical Pathways in Glaucoma_Zimmerman, Kooner_2001

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82 Primary Angle-Closure Glaucoma

Table 5–1. Differential Diagnosis of Secondary Angle Closure

Neovascular glaucoma

Central retinal vein occlusion

Uveitis

Iris bombé

Iridocorneal endothelial (ICE) syndrome

Following scleral buckling or panretinal photocoagulation

Malignant (ciliary block) glaucoma/aqueous misdirection

Ciliary body swelling, inflammation, or cyst

Phacomorphic glaucoma

Subluxated lens

Nanophthalmos

Posterior segment tumors

Under What Circumstances Does Primary Angle Closure

Occur? What Are Its Underlying Mechanisms?

RELATIVE PUPILLARY BLOCK

Relative pupillary block is, by far, the most common of the two mechanisms for primary angle closure.4 Predisposed eyes are usually small and hyperopic with crowded anterior segments. In such eyes, the contact between the lens and iris at the pupil is more snug than normal, as shown in Figure 5–1A. This lens–iris contact tightens with the enlargement of the crystalline lens as a normal consequence of aging. In predisposed eyes, at a critical pupillary diameter (4–6 mm), the resistance to the flow of aqueous from posterior chamber through the pupil and into the anterior chamber, called relative pupillary block, causes fluid pressure to build behind the iris as shown in Figure 5–1B. This pressure differential pushes the peripheral iris forward into the angle, against the trabecular meshwork, causing appositional and eventually permanent synechial angle closure, as illustrated in Figure 5–1C. As a result, the intraocular pressure (IOP) rises.

The possibility of inducing acute angle closure with pharmacologic mydriasis has contributed to a reluctance among primary care physicians to dilate the pupil for diagnostic ophthalmoscopy. In a predominantly black and Caucasian population, the risk of inducing angle closure by dilating the pupil is less than 1% and is approximately 0.3% if patients are screened for family history of glaucoma and for shallow anterior chamber with a penlight.5 The recognition of retinal disorders is greatly enhanced by mydriasis. Therefore, it would appear that the benefits of earlier detection of such a common blinding condition as diabetic retinopathy alone outweigh this small risk of angle closure from pharmacologic mydriasis.

Obviously, a peripheral iridectomy, as shown in Figure 5–2, eliminates relative pupillary block by providing an alternative route for aqueous to flow from the posterior chamber into the anterior chamber, thereby equalizing the pressure difference between the two. This allows the iris to fall away from the angle structures, relieving the angle closure in areas where it has not yet become synechially attached to the trabecular meshwork.

84 Primary Angle-Closure Glaucoma

As the name suggests, the iris plane in plateau iris is flat and not convex. As a result, the axial anterior chamber depth is normal, or nearly so, whereas the peripheral iris contour is abnormally convex and lies in close proximity or is apposed to the trabecular meshwork, as shown in Figure 5–3A. When the pupil dilates in such an eye, iris tissue is pushed against the trabecular meshwork, closing the angle. Ultrasound biomicroscopic studies have shown that the underlying anatomic mechanism for plateau iris is abnormally anteriorly placed ciliary processes.6,9 These ciliary processes, which lie just underneath the peripheral iris roll, cause plateau iris by holding the peripheral iris forward, even after iridectomy. Because plateau iris syndrome has nothing to do with resistance to flow of aqueous through the pupil, iridectomy does nothing to resolve it.

A B

C

Figure 5–3. Plateau iris configuration and syndrome (A) In most eyes with an iris in plateau configuration, this is the appearance of the iris prior to iridectomy. (B) The predominant mechanism for angle closure is actually relative pupillary block and is therefore relieved by iridectomy. (C) In those rare cases where angle closure/closability persist after iridectomy, the term plateau iris syndrome is used. (Modified from Shields MB: Textbook of Glaucoma, 4th ed. Baltimore: Williams & Wilkins, 1998:179.)

Terminology can be confusing, but is useful and important. When a plateaulike iris is observed with slit-lamp biomicroscopy and gonioscopy prior to iridectomy, as shown in Figure 5–3A, it is termed plateau iris configuration. Despite this appearance of the iris and chamber angle, and the surgeon’s suspicion that iridectomy may fail to open the angle, relative pupillary block is usually the predominant mechanism for the angle closure in a majority of these eyes and, as illustrated in Figure 5–3B, iridectomy is curative of the angle closure stimulus. If plateau iris and angle closability persist after iridectomy, this rare situation, shown in Figure 5–3C, is termed plateau iris syndrome. Plateau iris syndrome is rare, but should be ruled out following iridectomy in all eyes with primary angle closure. In addition, the surgeon should have a heightened index of suspicion for the presence of plateau iris in younger and/or myopic patients with primary angle closure.

Although it is usually detected during gonioscopy shortly after iridectomy, plateau iris syndrome may also appear years later. For this reason, careful gonioscopy should be performed periodically for the remainder of the patient’s life after iridectomy for primary angle closure, to detect progressive closure/ closability of the angle due to plateau iris syndrome. The plateau iris syndrome may vary in its anatomic degree, depending on the physical height of the iris plateau relative to the adjacent angle structures. If the plateau is opposite the anterior trabecular meshwork or Schwalbe’s line, when the angle is crowded, the trabecular meshwork is obstructed and the IOP rises. However, in some cases the plateau may only be as high as the scleral spur or posterior trabecular meshwork so that angle crowding does not cause trabecular obstruction and elevated IOP.

Epidemiology and Importance

What Factors Anatomically Predispose Eyes to Primary

Angle Closure?

AGE

The prevalence of increased relative pupillary block and primary angle closure increases with age, in tandem with the natural increase in volume of the crystalline lens and decrease in resting pupil diameter. The prevalence of primary angle-closure glaucoma peaks in the sixth decade, earlier than with primary open-angle glaucoma.

RACE

Among Caucasians, 75 to 90% of glaucoma cases are due to primary openangle glaucoma, affecting 0.5 to 2.16% of the adult population.10 This is in sharp contrast to the much lower prevalence of primary angle-closure glaucoma in this population, ranging from 0.09 to 0.17%. Population-based studies demonstrate that this relationship is reversed in Eskimos: 2.12 to 2.9% for primary angle-closure glaucoma compared to 0.01 to 0.4% for primary open-angle glaucoma.11–16 The prevalence of primary angle-closure glaucoma is 20 to 40 times higher among Eskimos than Caucasians.

86 Primary Angle-Closure Glaucoma

Primary angle-closure glaucoma in Asian populations has also been studied, albeit less extensively than in Eskimos. It appears that the prevalence of primary angle-closure glaucoma among Asians is intermediate between that in Caucasians and Eskimos. It has been estimated that primary angle-closure glaucoma affects more than 30 million people worldwide, at least as many as primary open-angle glaucoma.17

Primary angle closure is less common in blacks than Caucasians. When angle closure does occur in black patients, the chronic form is the most common.

SEX

Primary angle closure in Caucasians and especially among Eskimos, is more common in females, perhaps due to a smaller anterior segment. In black patients, the incidence of primary angle closure is equal in males and females.

REFRACTIVE ERROR

Refractive error definitely influences the likelihood of primary angle closure. Because hyperopes have smaller anterior segments than emmetropes or myopes, increased relative pupillary block and primary angle closure are more common in hyperopic eyes. In myopic eyes with primary angle closure, especially in younger patients, plateau iris syndrome should be suspected as a mechanism.

FAMILY HISTORY

Primary angle closure is believed to be inherited in some cases, although a positive family history does not predict the likelihood of a future attack of acute angle-closure glaucoma.

How Is Gonioscopy Most Effectively Used in the

Diagnosis and Management of Primary Angle Closure?

Gonioscopy should be performed on all patients with glaucoma, on all glaucoma suspects, and on all individuals suspected of having narrow angles. Without it, identification of the underlying mechanism and therefore the appropriate treatment of any glaucomatous condition is impossible. Skillful gonioscopy is important in the diagnosis of glaucoma, but also in its treatment, for example, in performing laser trabeculoplasty and laser gonioplasty.

Visualization of the angle structures requires a contact lens. Table 5–2 lists the common gonioscopic techniques with their respective advantages and disadvantages.

KOEPPE GONIOSCOPY

Koeppe gonioscopy is a direct method of visualizing the chamber angle by using a dome-shaped goniolens, an illumination system, and a hand-held biomicroscope.

88 Primary Angle-Closure Glaucoma

GOLDMANN AND INDENTATION GONIOSCOPY

Goldmann and indentation gonioscopy are indirect methods of visualizing the chamber angle in the mirror of a gonioprism with a slit-lamp microscope. Indirect gonioscopy provides an inverted image, but the right-left and updown orientations are maintained.

What Questions Should Be Answered with Gonioscopy in Primary Angle-Closure Glaucoma?

Three questions should be answered with gonioscopy when evaluating a patient for angle closure:

IS THE ANGLE OPEN OR CLOSED IN ITS NATURAL POSITION?

The ideal method of observing the angle in its natural position is Koeppe gonioscopy.18 However, special instruments are required and so, from a practical point of view, indirect gonioscopy is more convenient for most ophthalmologists. Clinicians should use the method with which they are most comfortable and confident. The avoidance of artificial distortion of the angle during gonioscopy, especially with indentation lenses, is crucial to the evaluation of the natural position of the angle.

IF ANGLE CLOSURE EXISTS, IS IT APPOSITIONAL (REVERSIBLE)

OR SYNECHIAL (PERMANENT)?

Indentation gonioscopy, as described by Forbes,19,20 is a technique wherein one uses a contact lens (Zeiss, Posner, Sussman, etc.) with a small area of corneal contact to push aqueous from the central to peripheral anterior chamber to artificially open the angle. Areas of appositional closure of the angle, in which the peripheral iris is resting upon but is not yet adherent to the trabecular meshwork, can be opened by moving the iris away from the angle structures with this dynamic indentation gonioscopy. This maneuver brings into view any peripheral anterior synechias where the iris is adherent to the angle.

The extent of synechial versus appositional closure is of critical importance because, following relief of relative pupillary block with iridectomy, the control of intraocular pressure will depend on the fraction of trabecular meshwork circumference not yet closed with synechias. Areas of synechial closure remain closed following relief of the angle closure mechanism and are therefore permanently unavailable for aqueous outflow except in certain cases of acute angle closure where fresh peripheral anterior synechias can be successfully broken with laser gonioplasty or surgical goniosynechialysis.21–23 The extent of appositional versus synechial angle closure was a much more serious issue prior to the introduction of laser iridectomy, when surgical peripheral iridectomy was required to relieve pupillary block. In cases where surgical iridectomy failed to control the IOP, a second trip to the operating room for a filtration operation was then necessary.

IF OPEN, IS THE ANGLE CLOSABLE?

It is not always possible to determine with gonioscopy if an angle is definitely closable. The examiner’s judgment and experience play a large role. In this situation, one is left with the option of proceeding with laser iridectomy or using other criteria, such as provocative testing, to try to assess the risk of future angle closure.

What Role, If Any, Does Provocative Testing Play in the Management of Primary Angle-Closure Glaucoma?

Provocative testing has little, if any, role. Before the availability of modern laser iridectomy techniques, the relief of pupillary block required a surgical iridectomy. Although relatively safe, this procedure poses the usual uncommon but unavoidable risks of intraocular surgery. In the past, to minimize unnecessary surgical iridectomies, provocative tests were employed to try to estimate the closability of the angle in a particular eye by inducing angle closure artificially. Although provocative tests are rarely used today, it is useful to be aware of their existence and physiologic bases.24–26

The ideal provocative test for angle closure would be physiologic, simple, not time-consuming, reproducible, and safe. No provocative test meets all of these criteria. A positive provocative test is no guarantee that a patient will indeed develop angle closure, just as a negative test does not assure immunity from a subsequent angle closure attack. Why, then, should one bother with provocative testing? These tests can be used as adjuncts to bolster one’s clinical impression, and they are useful in the rare circumstance where laser iridectomy is unavailable or not possible. Ultimately, the decision to treat an asymptomatic patient with laser iridectomy because of narrow angles rests on the clinical judgment of the ophthalmologist. If the ophthalmologist decides that laser iridectomy is not necessary in a patient with narrow angles, the patient should be alerted to the symptoms and dangers of acute and subacute angle closure and should have periodic examinations including careful gonioscopy. The role of provocative testing in answering the question of closability of the angle is minor, especially when one considers the availability and safety of modern laser iridectomy.

Diagnosis and Differential Diagnosis

How Does the Patient with Primary Angle Closure

Present to the Ophthalmologist?

Primary angle closure presents one of three clinical pictures: acute, subacute, or chronic:

ACUTE PRIMARY ANGLE-CLOSURE GLAUCOMA

Acute angle-closure glaucoma presents as an emergency with abrupt onset and rapid elevation in IOP. The striking signs and symptoms are listed in Table 5–3. The differential diagnosis of acute primary angle-closure glaucoma, as shown