Foster and associates have published a classification of angle-closure that has been widely used in prevalence studies and epidemiological research [7]. It specifies three stages: Primary angle-closure suspect (PACS), Primary angle-closure (PAC) and (PACG) in the progression of angle-closure from ITC and from signs of disease, such as elevated intraocular pressure and peripheral anterior synechia, to frank optic nerve damage as the result of chronically elevated pressure.

Ritch and Lowe [8] proposed a classification based on the angle anatomy and mechanisms of outflow obstruction. Primary and secondary angle-closures can also be classified mechanistically by the presence or absence of pupillary block and whether the iris is anatomically “pushed forward” or “pulled forward” to the trabecular meshwork (Table 14.2). Four successive anatomic levels of angle-closure have been described: iris (pupillary block), ciliary body (plateau iris), the lens (phacomorphic glaucoma), and vectors posterior to the lens (malignant glaucoma). Angle-closure may result from blockage of outflow with one or more of these anatomical changes, with one or more mechanisms involved. Pupillary block may occur to some degree in other forms of glaucoma and must be ruled out. A consensus statement from the 3rd Global Association of International Glaucoma Societies (AIGS) Consensus Meeting on Angle-Closure Glaucoma concluded the following: “Although the amount of pupillary block may vary among eyes with angle closure, all eyes with angle closure require treatment with iridotomy” [3].

The possibility to visualize the anterior segment structures with imaging techniques such as ultrasound biomicroscopy (UBM) and optical coherence tomography (OCT) has enhanced our ability to classify angle-closure glaucoma better anatomically, determine the mechanisms involved, and institute proper therapy. Imaging can often clarify nebulous situations, particularly if one clinician has found the angle to be open when another has not.

Plateau iris configuration and plateau iris syndrome are conditions that are often confused with pupillary block and PAC. Plateau iris configuration is an anatomically abnormal anterior segment configuration that has the potential to result in angle-closure. On gonioscopy in plateau iris, the root of the iris may be short and inserted more anteriorly on the ciliary face. This results in a plateau configuration with a shallow peripheral angle and a sharp drop-off of the peripheral iris. The anterior chamber may be of normal depth centrally and the iris only slightly convex.

Plateau iris syndrome may develop spontaneously or after pupillary dilation and may present with symptoms identical to an acute angle-closure (pupillary block) attack. In some cases, there may also be an additional element of relative pupillary block. Ultrasound biomicroscopy (UBM), when available, is especially useful in the assessment and differentiation of pupillary block and plateau iris configurations. Imaging under both light and dark conditions is helpful. In a recent study, Filho and associates compared the UBM findings between plateau iris configuration (PIC) and primary open-angle glaucoma with narrow angles (POAGNA) [9]. They found that PIC eyes are characterized by a more crowded anterior segment compared with POAGNA eyes. However, when the same parameters were evaluated between light and dark circumstances, no changes occurred.

The etiology of a glaucoma attack may not be appreciated without imaging. The episode is therefore often treated with laser iridotomy. An iridotomy may not open the angle or may only open it partially. An eye with an open laser iridotomy and plateau iris configuration may ultimately undergo an acute attack, confirming the diagnosis.

Laser peripheral iridoplasty can open the angle in plateau iris syndrome [10]. This technique is not readily embraced by all ophthalmologists – some voicing discomfort over the inflammatory changes created by the application of the laser to the iris. This technique employs argon laser burns of low power and large spot size to the peripheral iris adjacent to the angle to physically pull open the angle. The eye is pretreated with apraclonidine or brimonidine. The argon laser treatment parameters are set to produce contraction burns (500 μm spot, 0.5–0.7 s, 80–100 mW). The Abraham lens is used to place the burns as peripherally as possible. The laser power should be adjusted accordingly so that the spots produce contraction – not penetration. Failure to see any contraction is an indication of power being too low or that PAS is holding the iris to the sclera and preventing contraction. A full treatment requires from 20 to 24 spots over 360°. Overtreatment should be avoided. Approximately two spot diameters should be left between each spot, and radial iris vessels should be avoided. Postoperatively, the patient is treated with topical steroid drops with the pressure monitored as with any other glaucoma laser procedure [11]. A primary treatment of combined peripheral iridoplasty and laser iridotomy performed sequentially has also been proposed [12]. A patient with plateau iris configuration is susceptible to further shallowing of the anterior chamber with aging and may also develop pupillary block.

Angle-closure glaucoma has two pathophysiologic etiologies. The final common mechanism of each type is appositional obstruction of the trabecular meshwork by peripheral iris. This results in an impairment of aqueous outflow accompanied by a sudden (acute) or gradual (chronic) IOP increases. Raised IOP and subsequent glaucomatous damage to the optic nerve result either from mechanisms that push the iris forward from behind or from mechanisms that pull the iris forward into contact with the trabecular meshwork. Degrees of closure range from ITC with normal IOP and eventual to total trabecular outflow occlusion with elevated pressure and eventual PAS.

Primary angle-closure is caused by pupillary block that results in appositional and/or synechial closure of the anterior chamber angle. Conditions that were previously classified as primary angle-closure glaucoma, such as plateau iris, are generally associated with anatomic abnormalities of the anterior chamber. Conditions classified as secondary angle-closure glaucoma are associated with other ocular or systemic abnormalities.

In cases of primary acute angle-closure attack or an acute secondary angle-closure, the IOP can rapidly elevate to a dangerous level. Prompt diagnosis and treatment are paramount as blindness may ensue quickly.

Gonioscopy is essential to identifying the underlying anatomy and pathophysiology of angle-closure in order to properly classify the type of glaucoma and initiate treatment. Gonioscopy as a technique to visualize the anterior chamber angle was devised by Trantas in the 1880s [13]. His method employed indenting the sclera and viewing with a direct ophthalmoscope. Koeppe gonioscopy, a method rarely used today both because of the elaborate setup it requires and because it is time-consuming to perform, is an excellent method of “direct” gonioscopy. A dome-shaped Koeppe lens is applied to each eye with the patient in the exam chair in the recumbent position. The directly through the lens with a handheld source of magnification and illumination (Fig. 14.1a, b). The advantages of this method are that there is no distortion of the anatomy and that corresponding area of the angle in each eye can easily be compared by placing a lens on each eye and then viewing back and forth. The disadvantages of Koeppe lenses are that they require extra diagnostic equipment, cannot be used at the slit lamp, and do not allow for compression gonioscopy that would allow dynamic manipulation of the anterior chamber angle. Because the lens remains on the eye without any pressure from the examiner’s hands, there is no possibility that the act of holding the lens on the eye can deform the angle. Deformation of the angle is a common problem by novice gonioscopists.

Current commonly employed methods of gonioscopy are termed “indirect” because the lenses are mirrored and the portion of the angle viewed is 180° away, as seen through the mirror. The widespread use of gonioscopy following the introduction of the Goldmann lens in 1938 greatly improved the understanding of anterior chamber anatomy and the pathogenesis of the angle-closure glaucoma. The three-mirror Goldmann lens (Fig. 14.2) is the most versatile Goldmann-type lens because in addition to the mirror for examining the angle, the other portions of the lens can also be used to view the posterior pole and more peripheral retina. The two-mirror Goldmann and single-mirror Goldmann lenses are smaller and easier to manipulate at the slit lamp. The advantage of the Goldmann type of lens is that it does not distort the appearance of the angle. The disadvantage is that viscous gonio solution must be employed as a coupling agent between the lens and the patient’s corneal surface.

The original Zeiss lens is a pyramidal, silvered glass, four-mirror lens with a shallow corneal curvature on its ocular surface. Non-silvered versions with high-index glass, which afford an excellent view, are now available. The traditional lens is clipped into a retaining fork on a metal handle that is held in the clinician’s fingertips (Fig. 14.3a, b). One advantage of this lens is that it is convenient to use during a routine slit lamp examination, as it is placed directly on the tear film and does not require a sticky gonio solution. At the conclusion of the gonio exam, the cornea remains clean; there is nothing to rinse off from the eye. Another major advantage is that the Zeiss lens may be employed to perform “compression gonioscopy.” Compression gonioscopy is the intentional depression of the cornea with the gonioscopy lens to force fluid into the peripheral angle open in an attempt to widen or open it (Fig. 14.4). This technique is useful to determine if the narrow angle has appositional closure, synechial closure, or both [14]. The findings from this “dynamic gonioscopy” can aid the clinician in determining whether the patient would best benefit from laser iridotomy, trabeculectomy, or other glaucoma procedure. The disadvantage of the Zeiss lens is that the clinician must be wary not to unintentionally compress the cornea when initially viewing the angle structures and thus erroneously overestimate the depth of the angle or its susceptibility for closure. The Zeiss lens (and its derivatives) requires more skill by the examiner, than does the Goldmann lens, to get an adequate view of angle structures.

The Posner lens (Fig. 14.5) is a variation of the Zeiss-type lens with the four-mirror lens mounted on a wand-shaped handle. The Sussman lens (Fig. 14.6a, b) is a similar four-mirror lens mounted in a retaining ring and is directly held in the fingertips as is the Goldmann lens. The Posner and Sussman lenses are used in a similar fashion as the Zeiss lens to view the anterior chamber angle and to perform compression. In some patients, the corneal ocular surface curvature of these types of lenses does not well match that of the patient’s cornea, and it is difficult to get the tear film to fill the interface appropriately. In these instances, a single drop of a thick artificial tear solution can often remedy this problem. With experience, most ophthalmologists easily master the technique of using these gonio lenses that use only tears as a coupling medium.

Various grading systems have been proposed to describe the appearance of the AC angle and its probability of closure [15].

The findings of the gonioscopy exam may be diagramed on a chart of concentric rings (Fig. 14.7a) with pathology such as closure or synechiae charted (Fig. 14.7b, c).

Gonioscopy lenses have therapeutic as well as diagnostic uses. In cases of acute angle-closure attacks, dynamic gonioscopy (with Zeiss, Posner, or Sussman lenses) can sometimes be used to interrupt the attack by compressing the cornea to relieve apposition and forcibly opening the peripheral angle after medical therapy has been initiated. The flat, nonsilvered portion of these lenses (between the mirrors) may also be applied to a filtering bleb after trabeculectomy surgery to compress the conjunctiva and visualize the underlying sutures to perform laser suture lysis when a lens dedicated for this purpose is not available. Gonioscopy is discussed in greater detail in Chap.​ 10.

Angle-closure results from appositional obstruction of the trabecular meshwork by the peripheral iris. This can be a consequence of an abnormal relationship between the size and position of the structures of the anterior segment and the relative pressure differential between the anterior and posterior chambers. Blockage of the meshwork may occur by forces acting at four successive anatomic levels, as proposed by Ritch et al. [8]. The first anatomic level described is at the iris. Mechanistically, this is the site of pupillary block. The next anatomic level is at the ciliary body, the level at which plateau iris syndrome occurs. The third level is the lens, which is involved in phacogenic mechanisms. The fourth anatomic level relates to forces posterior to the lens. This level has therefore been described as retinovitreal or uveal. Mechanistically this level is the site of malignant glaucoma and secondary angle-closure syndromes. Furthermore, each level of block can have some component of block of the level preceding it, creating a situation in which multiple mechanisms should be considered and treated. Anterior segment abnormalities – such as inflammatory, fibrotic, or fibrovascular conditions – can pull the peripheral iris forward to cause appositional and eventual synechial closure of the angle. Pupillary block, plateau iris, aqueous misdirection, or posterior segment abnormalities – such as choroidal swelling, choroidal hemorrhage, choroidal detachment, tumor, or space occupying lesions – can push the iris forward from behind to cause appositional and eventual synechial closure of the angle (Table 14.2). Of these various mechanisms, pupillary block is by far the most common. Further, the mechanisms are not mutually exclusive, and relative pupillary block may be present.

Primary angle-closure glaucoma is associated with relative pupillary block in most of the cases [23, 24]. It must be differentiated from plateau iris configuration and lens-induced secondary pupillary block. Risk factors for developing primary angle-closure glaucoma are well established and are discussed in the following sections.