Fine-tuning the diagnosis of angle closure

As our ability to identify angle closure expands, so does our understanding of the disease.

By Angelo P. Tanna, MD

On a global level, primary angle-closure glaucoma affects 16 million persons of whom 25% are legally blind.¹ Gonioscopy is the reference standard for the detection of angle closure; however, optical coherence tomography (OCT) and ultrasound biomicroscopic (UBM) imaging of the anterior chamber angle may add important information that can assist the ophthalmologist in making a better assessment of the angle anatomy.

CLASSIFICATION

Relationship to glaucoma

Before we proceed, please notice that the word “glaucoma” is not in the title of this article. Despite the long history of terms such as “acute angle-closure glaucoma” in the medical literature, a recent revision in the nomenclature dictates that we use the term “glaucoma” only in the presence of a glaucomatous optic neuropathy.

A patient with typical risk factors for angle closure such as Asian ethnicity, female, and hyperopia who presents with an IOP of 50 mm Hg, corneal edema, a closed anterior chamber angle, no secondary features, and an occludable angle in the fellow eye has acute primary angle closure, not acute angle-closure glaucoma. Somewhat surprisingly, most patients who present with acute primary angle-closure recover without the development of glaucomatous optic neuropathy.

The focus of this article is on the detection of the asymptomatic forms of primary angle closure.

Three types

These definitions represent the most widely accepted modern nomenclature for the diagnostic classification of primary angle closure.

Primary Angle Closure Suspect: ≥ 180 degrees iridotrabecular apposition identified on nonindentation gonioscopy in the setting of statistically normal IOP (≤ 21 mm Hg) and in the absence of peripheral anterior synechiae (PAS).

Primary Angle Closure: ≥ 180 degrees iridotrabecular apposition identified on nonindentation gonioscopy with statistically elevated IOP (> 21 mm Hg) or PAS or both.

Primary Angle-Closure Glaucoma: primary angle closure, as defined above, with glaucomatous optic neuropathy.

GONIOSCOPY

When to perform

Despite modern imaging technology such as OCT and UBM, gonioscopy remains the most common method for angle closure detection. Studies show gonioscopy is often not performed in patients with glaucoma, as recommended by the AAO’s Preferred Practice Patterns.²

Gonioscopic view of the left eye of a patient with a history of narrow angles for which she was treated with laser iridotomy in both eyes. Despite the presence of a patent iridotomy, she continues to experience episodes of pain and blurry vision in the left eye.
(A) Nonindentation gonioscopy discloses a closed iridocorneal angle.
(B) Indentation gonioscopy shows peripheral anterior synechiae (PAS) at 5 o’clock (red arrow indicates location of PAS); however, the remainder of the inferior angle can be opened to the ciliary body band. Note the corneal striae that result from indentation, slightly diminishing the quality of the view of the angle.

In my opinion, comprehensive ophthalmologists should perform gonioscopy on any patient whose anterior chamber angle appears shallow, as determined by slit lamp biomicroscopy; they should also perform it on hyperopic patients and patients with glaucoma and those under suspicion of glaucoma.

Patient comfort

Successful gonioscopy requires patient cooperation. Before you start, make sure the patient understands what will happen during the examination. Explain that the lens will touch their eye and that he will feel the lens touch his eyelids, but he will not have pain. I often tell patients that the natural response is to reflexively blink, but they must use “brain power” to overcome this reflex.

Test in the dark

For detecting a narrow angle, I prefer using a gonioprism with four-mirror lenses. These devices allow the examiner to perform indentation gonioscopy, a technique that allows differentiation angle closure due to PAS from appositional angle closure. The examination must be performed in a dark room.² The examiner must minimize the amount of light entering the pupil by using a low level of slit lamp illumination and a short, narrow beam. Excessive light exposure during gonioscopy will result in pupil constriction and, possibly, a false assessment of the anterior chamber angle as not occludable.

After applying the lens to the ocular surface, the examiner must verify the absence of corneal striae — for two important reasons. First, the view of the angle will be degraded. Second, an otherwise closed angle may be opened by the force of indentation of the cornea.

Trabecular meshwork

The anterior chamber angle should be systematically examined to determine if the trabecular meshwork is visible. In most patients the posterior portion of the trabecular meshwork is pigmented to varying degrees. If the posterior portion of the trabecular meshwork is not visible, this may represent iridotrabecular apposition or PAS. One must differentiate between these by performing indentation. If PAS are present, indentation of the cornea will not open that portion of the angle.

COMMON ERRORS

Lightly pigmented trabecular meshwork

Ophthalmologists may encounter two common pitfalls in the detection of angle closure. In eyes with a particularly lightly pigmented trabecular meshwork, ophthalmologists sometimes misinterpret the anatomy and think the angle is closed. Indentation will disclose the scleral spur if it is not already visible and that will allow the examiner to confirm the angle is, in fact, open.

Sampaolesi’s line

Sampaolesi’s line represents pigment deposition anterior to the trabecular meshwork. If confused for the trabecular meshwork itself, the examiner may falsely conclude the angle is open. The examiner should make sure the scleral spur is visible. Visualizing and identifying all the angle structures may require indentation.

Continuing education

The art of gonioscopy is difficult to teach and difficult to learn. Readers interested in enhancing their abilities in practicing this important examination technique would be well served to review the website gonioscopy.org, run by the University of Iowa’s Lee (Wallace L.) Alward, MD. The site is replete with instructive videos of gonioscopic views of anterior chamber angle images.

MECHANISM

Pupillary block

The most common underlying mechanism for the development of primary angle closure is pupillary block. Many anatomical characteristics have been associated with an increased risk for angle closure, including a shallow anterior depth and short axial length as well as many newly identified factors such as iris thickness, lens vault, and others.³

Plateau iris

It is becoming increasingly clear, however, that many eyes with angle closure have persistent iridotrabecular contact even after the creation of a patent iridotomy with the elimination of pupillary block. This condition, known as plateau iris, sometimes requires additional treatment.

Plateau iris can only be reliably diagnosed after creation of a laser iridotomy. In plateau iris configuration, the central anterior chamber is usually of normal depth. The iris configuration is flat (as opposed to anteriorly bowed in the setting of pupillary block) as it extends peripherally; however, just prior to its insertion into the anterior chamber angle there is a roll in the iris and it bends steeply posteriorly. Indentation gonioscopy often discloses a “double hump sign.” Pupil dilation results in neither angle closure nor an IOP elevation in the setting of plateau iris configuration. In plateau iris syndrome, however, although the gonioscopic appearance is the same, dilation results in angle closure and IOP elevation.⁴

ADVANCED IMAGING

OCT imaging

OCT and UBM imaging of the anterior chamber angle represent a major advance in our ability to understand the underlying pathophysiology of angle closure and to help properly diagnose and classify difficult cases such as plateau iris. In general, OCT imaging (Figure 1, page 59) allows visualization of the structures of the anterior chamber angle and allows quantification of various structural features of the angle. Those capabilities make this technology a powerful tool for research. I believe it is also helpful for demonstrating the anterior chamber angle anatomy for clinicians not proficient with gonioscopy.

Figure 1: Anterior segment OCT image of an eye with a narrow angle.
COURTESY ROBERT M. FELDMAN, MD

UBM IMAGING

UBM can be used to image the ciliary body, its relationship to the iris and its effect on the iridocorneal angle. It is particularly useful for determining if the anatomical characteristics of plateau iris syndrome are present, such as anterior displacement of the ciliary body (Figure 2). Additionally, it is useful for the detection of ciliary body effusions associated with secondary nonpupillary block-angle closure, for example, in the idiosyncratic reaction that may occur in patients on topiramate (Topamax, Janssen Pharmaceuticals).

UBM of the anterior chamber angle (Figure 2) discloses a closed angle and an anteriorly situated ciliary body, characteristic of plateau iris syndrome.

Despite modern technology, gonioscopy remains the most important examination technique for assessment of the anterior chamber angle and detection of primary angle closure. For the benefit of their patients, ophthalmologists should aim to master this skill. OM

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About the Author
	Angelo P. Tanna, MD, is vice chairman and associate professor of ophthalmology and director of the glaucoma service at the Northwestern University Feinberg School of Medicine in Chicago. Disclosure: Dr. Tanna has no relevant conflicts to disclose.