Healio
Healio
August 22, 2011
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Treating Angle-Closure Glaucoma

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Narrow angles are found in a spectrum of disease. Primary angle-closure suspects (PACS) exhibit narrow angles without any anatomic or functional evidence of pathology. Primary angle closure (PAC) is characterized by narrow angles with eitherperipheral anterior synechiae or elevated IOP. Primary angle-closure glaucoma (PACG) is distinguished by narrow angles with optic nerve injury.

Angle-closure glaucoma comprises about 25% of glau-coma cases, yet is responsible for nearly 50% of all glaucoma-related blindness. Prevalence data from Mongolia and Singapore suggest that the bilateral blindness rate for angle-closure glaucoma is 3-fold to 10-fold higher than for open-angle glaucoma, reaching almost 40% in Mongolia.1 However, a 5-year population survey in India showed that only about 20% of patients with PACS will progress to PAC, and just under 30% of patients with PAC will further progress to PACG.2,3 Thus, the challenge is to identify which patients need treatment and how efficacious those treatments are. The purpose here is to discuss the major surgical treatment options: iridotomy/iridectomy, iridoplasty and lens extraction.

Iridotomy

The importance of an iridectomy in treating “congestive glaucoma” (i.e., acute angle closure) was first recognized just before the turn of the 20th century. In 1920, Edward Curran was the first to treat and cure patients with acute or chronic angle-closure glaucoma with an iridotomy using a fine Knapp knife-needle.4 Nearly a century later, iridotomy has become the standard of care for patients with acute and chronic angle closure.

Evidence supporting the use of iridotomy in the fellow eyes of patients with acute angle-closure attacks is abundant. The first nonrandomized retrospective analysis of fellow eyes treated with observation, pilocarpine or surgical iridectomy was reported in 1962.5 Of the 113 eyes not treated with an iridectomy, 58 went on to develop an angle-closure attack (in some cases, as late as 15 years later) whereas of the 54 cases treated with iridectomy, only one case developed acute angle closure (with a non-patent hole).

By the mid-1990s, iridotomy using the Nd:YAG laser was clearly safer than iridectomy and equally efficacious, completely preventing acute attacks in fellow eyes.6,7 Chronic pressure elevations are also rare in fellow eyes treated with laser iridotomy.8 But 40% to 60% of the eyes that had the acute attack will develop chronic pressure elevations requiring eye drops, despite patent iridotomies.9-11

The utility of laser peripheral iridotomy for chronic forms of angle closure is less clear. Gonioscopy and ultrasound biomicroscopy in PACS have confirmed that asymptomatic narrow angles deepen with iridotomy, suggesting the role of a relative pupillary block.12,13 However, very few data demonstrate that laser iridotomy alters the course of angle-closure diseases from PACS to PACG. The Zhongshan Angle Closure Prevention trial underway in Guangzhou, China, is designed to evaluate both the natural history of untreated narrow angles and the effect of laser iridotomy in preventing elevated IOP, peripheral anterior synechiae and acute angle-closure attacks.14

Iridoplasty

Laser iridoplasty, first attempted in the 1970s, has evolved to use the argon laser to place multiple long, low-energy burns in the iris periphery and use the resulting stromal contraction to pull the iris root away from the trabecular meshwork. The technique can be performed with or without a contact lens, following application of 1% pilocarpine, and involves placing 20 to 30 spots, 360˚ around the iris, as peripheral as possible. The laser settings most commonly described and those used in our clinic, consist of a large spot size (500 μm), long-duration application (0.4 to 0.5 sec) and low starting energy (200 mW), with the latter titrated up until stromal contraction is observed. Although not commonly done in most practices, laser iridoplasty has found a niche in two clinical settings: acute angle closure not amenable to peripheral iridotomy and persistently narrow angles despite a patent peripheral iridotomy (with or without elevated IOP).

Figure. Iridotomy

Iridotomy has become the standard of care for patients with acute and chronic angle closure.
Source: David Friedman, MD

Click here for a larger view of this image.

In the acute angle-closure setting, severe corneal edema often precludes the use of the YAG laser to make a peripheral iridotomy. Although edema is theoretically alleviated by topical hypertonic agents, practicality and efficacy limit their utility. Moreover, iridotomy can be difficult in patients with thick iris stroma. As an alternative, iridoplasty can be considered. One study randomized patients with acute angle-closure attacks in which an iridotomy could not be performed, to either medical therapy using intravenous acetazolamide with mannitol as needed, or peripheral laser iridoplasty.15 While no difference in IOP was observed, iridoplasty did normalize the mean IOP within 1 hour of treatment—significantly faster than medical therapy.16,17 With sufficient peripheral chamber depth, iridoplasty can be considered as a treatment for acute angle closure when iridotomy is not possible.

For chronic angle-closure states, data supporting laser iridoplasty are lacking.18 Many patients with PAC continue to have elevated IOP after iridotomy, suggesting that non-pupillary block mechanisms contribute to the compromised outflow. One of these mechanisms is plateau iris syndrome, whereby the peripheral iris is held up against the trabecular meshwork by the ciliary body and, by definition, in the presence of a patent iridotomy. A retrospective case series reviewed 14 patients with plateau iris syndrome and showed that laser iridoplasty produced a sustained opening of the angle, but had no effect on IOP.19 The only randomized trial comparing laser iridotomy to iridotomy plus iridoplasty, in patients with PACG or synechial PAC, showed no difference in pressure lowering at 1 year.20 Thus, while anatomic features of the iris probably contribute to the non-pupillary block component of angle closure, whether iridoplasty effectively remedies any of them remains to be seen.

Cataract Surgery

The lens thickens and moves anteriorly with age, which shallows the anterior chamber depth and is thought to contribute to narrowing of the angle through both fluidic (i.e., relative pupillary block) and mechanical mechanisms (such as those that define plateau iris).21 Consistent with this process, ultrasound biomicroscopy has shown that removal of the lens leads to a deepening of the angle (unexpectedly, though, the mechanism may also involve posterior movement of the ciliary body processes).22

Numerous case series have reported angle widening and IOP lowering from cataract surgery in patients with PAC or PACG, but as yet, no randomized clinical trials have compared standard care to lens extraction.23,24 The best data so far come from two trials comparing phacoemulsification with combined phacoemulsification plus trabeculectomy in patients with either medically controlled or uncontrolled PACG.25,26 The results showed a trend toward greater IOP lowering and a statistically significant difference in the number of glaucoma drops needed to control IOP in the combined arms of the studies.

However, even cataract surgery alone led to a substantial reduction in IOP and use of glaucoma eye drops. The clinical equipoise certainly exists to determine whether cataract surgery (or even clear lens extraction) should be considered as an early treatment for chronic angle closure. The EAGLE trial in Asia and the United Kingdom is set to test this question by randomizing PACG patients to early lens extraction versus conventional therapy (iridotomy, medical therapy and then filtering surgery).27

As with iridotomy and iridoplasty, the data are better for lens extraction as a therapy for acute angle-closure attacks. Since IOP can rise after acute angle attacks, presumably from the formation of peripheral anterior synechiae or from microscopic trabecular meshwork damage, investigators asked what therapy could best prevent future elevations in IOP.10 The trial randomized patients with acute angle-closure attacks aborted by medical therapy to either early cataract surgery or laser peripheral iridotomy. While neither group had a repeat angle-closure attack, only 3.3% of those in the cataract arm developed a pressure over 21 mm Hg (off drops) in 18 months of follow-up as opposed to 46.7% of those in the laser peripheral iridotomy group. Although the results clearly favor early cataract surgery, the clinical significance is less clear. Both groups had mean pressures in the low to mid teens on medication, and therefore, the main advantage was a reduction in the number of eye drops. At the very least, early cataract surgery should be considered for patients with acute angle-closure attacks, particularly those presenting with very IOP.

The Best Procedure

Evidence for laser treatments in suspect and established angle-closure glaucoma is weak. The strongest evidence is in the case of acute angle-closure attacks where iridotomy for the fellow eye clearly prevents attacks and iridoplasty can break them. Cataract extraction appears to lower ocular pressure after acute attacks as well in the attack eye, and may also be a good approach for patients with established angle-closure glaucoma. Clinical trials underway will supply important pieces of evidence to help guide clinicians in treating these patients

References

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  2. Thomas R, George R, Parikh R, Muliyil J, Jacob A. Five-year risk of progression of primary angle closure suspects to primary angle closure: a population based study. Br J Ophthalmol. 2003;87(4):450–454.
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  4. Curran E. A new operation for glaucoma involving a new principle in the aetiology and treatment of chronic primary glaucoma. Arch Ophthalmol. 1920;49:131–155.
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