Point-Counterpoint: Laser Peripheral Iridotomy for Primary Angle-Closure Glaucoma

Point: Dr. Pathik Amin

Primary angle-closure glaucoma affects more than 20 million people worldwide and is known to have a greater likelihood of bilateral irreversible blindness compared with primary open-angle glaucoma.¹ The standard treatment for decades has been laser peripheral iridotomy, which is indicated to prevent or treat a suspected pupillary block by opening an alternative pathway for aqueous flow, thereby equalizing the pressure between the anterior and posterior chambers. Using a classification system for primary angle-closure disease spectrum is important for management considerations. Table 1 outlines the modern classification system for primary angle-closure disease.

In the setting of an acute angle-closure crisis with a pupillary block mechanism, laser peripheral iridotomy is a well-established treatment. This should be performed once the intraocular pressure is adequately lowered through medical glaucoma therapy, which can serve to improve clarity of the media and increase safety. The fellow eye of a patient with acute angle-closure crisis should also be evaluated for a prophylactic laser peripheral iridotomy as 50% of patients will suffer an acute angle-closure attack in the fellow eye within 5 years.^2,3

In primary angle-closure suspect eyes, laser peripheral iridotomy increases angle width and has a good safety profile; approximately 96% of patients do not need additional intervention.⁴ Although the Zhongshan Angle-Closure Prevention (ZAP) trial found an overall low risk of angle closure in this subset of patients with observation alone, there was significant effect for prophylactic laser peripheral iridotomy—reducing the risk of progression to primary angle closure by 50%. Given that the population was purely Chinese, the results may not be generalizable to patients of other racial and ethnic groups.

Patients with primary angle closure or primary angle-closure glaucoma strongly benefit from treatment, and historically that has been in the form of laser peripheral iridotomy.⁵ In the EAGLE study, clear-lens exchange showed a greater efficacy with intraocular pressure and quality of life measures and was more cost-effective than laser peripheral iridotomy in patients with presbyopic primary angle-closure glaucoma or nonacute primary angle closure with high intraocular pressure.⁶ However, the study did not address patients with primary angle closure with low intraocular pressure who met the classification criteria on the presence of peripheral anterior synechiae. Because complications arising from laser peripheral iridotomy are uncommon, patients presenting with peripheral anterior synechiae of less than 50% of the angle may do well with laser peripheral iridotomy alone. For patients with primary angle-closure glaucoma that are prepresbyopic, it remains reasonable to perform laser peripheral iridotomy and monitor until their risk elevates or cataracts develop. Similar considerations apply to patients with active retinal disease requiring frequent dilation or who are in more rural areas with lack of access to medical care. Future multicenter randomized controlled trials may help provide more definitive guidance on the management of such cases.

Counterpoint: Dr. Lisa M. Young

Laser peripheral iridotomies have long been the gold standard to prevent angle closure−related pupillary block. Historically, this procedure has been the primary intervention used throughout the entire spectrum of primary angle closure, theoretically increasing the angle width in order to prevent acute angle-closure events, lower intraocular pressure, and decrease risk of glaucoma progression. Although this procedure still plays a critical role in the angle-closure spectrum, the historically low threshold for its application has been recently challenged and requires us to evolve our thinking about laser peripheral iridotomy.

Although the literature suggests that this laser is most beneficial in primary angle-closure suspects,⁷ it has also been suggested that laser peripheral iridotomy may be overperformed, even for this particular subset. Data from the 6-year Zhongshan Angle-Closure Prevention trial demonstrated that we would need to treat 44 patients in order to prevent one conversion to primary angle closure, and the 14-year data suggest that we would need to treat 12.35 patients to prevent that one conversion. Given this low rate of progression, observation is now considered as a reasonable approach for the majority of primary angle-closure suspects. Subsequently, it has been recommended that laser peripheral iridotomy should be considered merely for high-risk populations, including those with higher intraocular pressure at baseline, a shallower limbal anterior chamber depth, or a smaller central anterior chamber depth⁸ or those living in regions with inadequate access to health care.

Laser peripheral iridotomy is less likely to suffice as the lone therapy for patients with primary angle closure, acute primary angle closure, and primary angle-closure glaucoma. These patients continue to need close monitoring following laser peripheral iridotomy, and many require subsequent treatments in order to adequately control progression of the disease. Recently, the EAGLE study demonstrated that clear lens extraction shows superior intraocular pressure lowering when compared with laser peripheral iridotomy plus subsequent topical therapy for patients with primary angle closure and primary angle-closure glaucoma, with 21% needing further treatment after clear lens extraction as compared with 61% of those that had laser peripheral iridotomy and continue to be treated with at least one glaucoma drop.⁶ In fact, patients undergoing initial clear lens extraction are 10× more likely to maintain drop-free good intraocular pressure control than those with initial laser peripheral iridotomy, subsequently leading to less need for surgical intervention.⁹ Not surprisingly, after having cataracts removed, clear lens extraction also improved visual function and spectacle independence, as well as provided an overall better quality of life for these patients,⁶ which as providers should resonate with us all.

The goal continues to be safe, efficacious, and cost-effective therapy in order to prevent optic nerve damage and progression of glaucoma. It is no longer justified to indiscriminately use laser peripheral iridotomy as a band-aid for the primary angle-closure spectrum. Literature now supports monitoring the majority of patients with primary angle-closure suspects, performing laser peripheral iridotomy only as indicated in high-risk primary angle-closure suspect cases, and performing clear lens exchange for patients with elevated intraocular pressure and/or optic nerve damage secondary to angle closure.