26

Angle-Closure Glaucoma

Evaluation and Treatment After Iridotomy

Mina Pantcheva, MD; Malik Y. Kahook, MD; and David L. Epstein, MD, MMM

ROUTINE FOR EVALUATION OF PATIENT AFTER LASER IRIDOTOMY

The steps of handling patients’ eyes before and immediately after laser iridotomy are detailed in Chapter 56.

In brief, eyes are pretreated with 1% to 2% pilocarpine to stretch and thin the iris and to aid in peripheral placement of the iridotomy; they are also given alpha-adrenergic agonist to blunt a potential intraocular pressure (IOP) spike post-treatment by decreasing aqueous humor formation and to lessen the chance of iris bleeding with the yttrium-aluminum-garnet (YAG) laser by a vasoconstrictive action (see Chapter 12). Patients are then postoperatively treated with mild anti-inflammatory agents, such as weak steroids or nonsteroidal anti-inflammatory agents 4 times a day for 5 days and appropriate antiglaucoma therapy. The following section deals with the conceptual steps in the subsequent post-laser management.

Management begins with an evaluation before the laser as to the likely final diagnosis (ie, the likelihood of a combined open-angle and angle-closure mechanism) and thus the likelihood of a laser-induced IOP spike in the short term and residual open-angle glaucoma in the long term (see Chapter 23). This tentative understanding also aids in planning the needed frequency of patient visits after the laser procedure (Table 26-1).

The patient is seen the day after the iridotomy and every several days if the IOP is substantially elevated (in which case gonioscopy should be performed). Anti-inflammatory therapy can be extended if needed. Then, the patient is seen 7 to 10 days later when routine follow-up gonioscopy is performed. This visit is a convenient time to perform a prophylactic laser iridotomy on the fellow eye, assuming there are no residua in the first eye. The patient is routinely asked if the first eye is back to baseline before performing a prophylactic iridotomy on the fellow eye. (This is modified if there are urgent reasons to proceed more quickly with laser iridotomy in the second eye.)

Gonioscopy identifies the need for argon laser gonioplasty that might be planned a few weeks later and also allows correlation of the amount of synechiae with the measured IOP. IOP may be elevated for a few weeks after laser (and also surgical) iridotomy by an open-angle mechanism due to pigment or debris and the use of corticosteroids. Therefore, short-term antiglaucoma therapy (usually aqueous humor suppressants) is used only to protect against acute optic nerve damage, and an observed slightly high IOP, if safe for the optic nerve in the short term, might be tolerated for a few weeks to evaluate, at a subsequent visit, the true steady state. On the other hand, if more vigorous antiglaucoma therapy is initiated and the IOP later decreases into a range below the target, the need for continuation of such strong therapy should later be reevaluated.

The patency of the iridotomy is assessed. At any visit during the 4- to 6-week post-laser period, late closure of the iridotomy may occur. This is much more common after argon laser iridotomy, but is still occasionally observed after YAG iridotomy. (If patent at the 6-week visit, it is rare for any laser iridotomy to close subsequently, except in patients with uveitis or neovascularization.) However, even if obviously patent, an iridotomy may be sequestered in the sense that there are adhesions between the posterior iris surface and the crystalline lens so that there is not free communication between the posterior and the anterior chamber. The iridotomy may be too central (especially if pre-laser pilocarpine was not used or the pupil was semi-dilated and fixed from the acute angle-closure attack) and, therefore, may not clear the equator of the crystalline lens. The iridotomy very rarely might be too small in size (less than 50 μm) or filled with iris stromal strands or some potentially plugging iris material on the posterior border. Many of these complications were more commonly encountered after argon laser iridotomy than YAG laser iridotomy, but are still sometimes observed.

Therefore, in addition to observing the apparent direct patency of the iridotomy, the functional status needs to be assessed separately by observing the contour of the iris. Has the relative pupillary block been alleviated? If so, and there is resulting free communication between the posterior and anterior chambers through the iridotomy, the iris contour configuration should no longer be convex forward (an effect of increased fluid pressure in the posterior chamber). Sometimes, the crystalline lens convexity itself will hold the central iris forward from direct pressure, but the contour of the peripheral iris needs to be assessed by gonioscopy. Similarly, the peripheral chamber depth on slit-lamp examination (Van Herick’s rule1) should have also deepened, reflecting the induced loss of iris convexity. If these findings are not observed, then the clinician needs to entertain the possibility that there is not a functionally patent iridotomy or that the patient has some other form of angle-closure glaucoma, such as plateau iris, or some entity with direct peripheral pressure on the peripheral posterior iris surface (eg, ciliary body cysts or detachment).

If pupillary block has not been alleviated, then the angle may still appear closed by gonioscopy. Thus, apparent synechiae may not be true synechiae but merely continued appositional closure. Therefore, repeat indentation gonioscopy after iridotomy because, if there is a patent iridotomy, then fluid pressure cannot be holding the peripheral iris in appositional closure over the trabecular meshwork (TM). Thus, with a patent iridotomy, indentation should not change the apparent amount of angle closure, in which case it would have to represent peripheral anterior synechiae formation. If indentation does open the angle, then either the iridotomy is not patent or there is some secondary cause of the closure.

Mirrored lenses, unfortunately, despite their advantages, have their greatest weakness in this post-laser iridotomy assessment of peripheral iris contour. Although there is free communication between anterior and posterior chambers, sudden indentation displacement of the anterior chamber contents with the Zeiss-style indentation lenses does seemingly cause a temporary posterior indentation of the iris in many, but not all, patients. (The volume displaced by the indentation from the anterior chamber cannot pass quickly enough through the iridotomy into the posterior chamber, and thus posterior iris movement is commonly produced.) This induced posterior movement of the iris makes it easier to see into the angle, but should not thereby change the functional status of the angle if there is a patent iridotomy. Such persisting posterior movement of the iris after iridotomy has led to much confusion for the glaucoma student. In an eye with a patent iridotomy and no other cause for angle closure except primary pupillary block, appositional closure of the angle cannot exist by definition. If it looked that way with this indirect approach, it was because the mirrored gonioscopy lens did not present a true view of the angle (commonly because there is a large crystalline lens holding the central half, but not the peripheral portion, of the iris forward). It is crucial to distinguish between central iris convexity, due directly to the position of the crystalline lens, and peripheral iris convexity, due to increased fluid pressure in the posterior chamber, because at this post-laser visit one must be sure that relative pupillary block is no longer present (Figure 26-1). If the examiner is uncertain, Koeppe gonioscopy should be performed, as it readily allows such discrimination.

If pupillary block has been eliminated, but the angle remains either closed or very narrow and therefore occludable, and this is not due to a misinterpretation from an indirect mirrored view or a large crystalline lens, then other diagnoses should be entertained at this post-laser visit. The possibility of peripheral anterior synechiae, or secondary direct mechanical closure from the ciliary body (see Chapter 29) producing continuing appositional closure, or a plateau iris should be considered (Figures 26-2 and 26-3). A mydriatic (using a sympathomimetic not a cycloplegic drug) provocative test to one eye can be performed, either at the 1-week visit or more often at a visit several weeks later, to rule out plateau iris.

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