Angle-closure glaucoma needs further understanding, more targeted treatment

Issue: March 25, 2013

Recent data show that the prevalence of primary angle-closure glaucoma is higher than previously estimated, not only in Asia but also in Europe and among Caucasians, in general, according to one specialist.

In a keynote lecture at the European Glaucoma Society meeting held in Copenhagen, Denmark, Paul Chew, MD, said that laser iridotomy alone does not seem to provide sufficient control of primary angle-closure glaucoma (PACG), and further studies are needed to find alternative ways of addressing the disease.

“We need to clarify the underlying mechanisms of the disease to find more specific, long-lasting strategies,” he said.

Prevalence

PACG is estimated to affect 30 million individuals worldwide, 87% of whom are in Asia. In China, 1.7 million people are bilaterally blind from glaucoma, 91% due to angle closure. Singapore has the highest reported prevalence: 12.2/100,000 per year in people aged 30 years or older. Japan has a reported prevalence of 0.6%.

The prevalence is lower in Western countries. However, it is now two to four times more common than previously reported. It currently affects 0.4% of patients older than 40 years of age. Approximately 1.6 million people in Europe are affected, with a further 9% increase predicted within the next decade. Three-quarters of those affected are women.

“From epidemiological data, we are learning that shallow anterior chamber, short axial length, thick crystalline lens, female sex and Chinese ethnicity are the most prominent risk factors,” Chew said.

Angle closure mechanism

Pupil block, angle crowding, plateau iris configuration and lens thickness are possible causes of primary angle closure and PACG and may occur alone or in any combination, Chew said. Laser peripheral iridotomy is currently the standard treatment protocol but is not successful in all patients; appositional angle closure persists after treatment in approximately 20% to 30% of patients with primary angle closure or PACG.

“It is important to determine angle closure mechanism to tailor the treatment accordingly. [Anterior segment optical coherence tomography] is a useful tool and may assist clinicians to plan a more targeted treatment,” Chew said.

Treatment should also be prompt and aggressive, he said.

“Studies have found that the duration of symptoms before presentation and the time taken to abort acute attacks is significantly associated with the development of PACG,” he said.

The socio-economic conditions of some parts of Asia probably account for the inferior outcomes, and more recent studies already show improvement, with a longer duration of the IOP-lowering effects and good visual acuity outcomes.

A 2004 study demonstrated a 58% rate of relapse, largely occurring just 6 months after laser peripheral iridotomy, with one out of five patients becoming blind within 6 years. In a more recent study, relapse occurred in 21% of patients within 1 year. At final follow-up, IOP was well-controlled without medications, and visual acuity was between 20/20 and 20/40 in 90% of eyes.

As an alternative to laser peripheral iridotomy, iridoplasty has been shown to be useful in primary angle closure unresponsive to medical treatment but has not been studied adequately, Chew said. Its limited and unsustained effect in many cases of primary angle closure may be due to severe and progressive angle crowding.

Generally speaking, a better understanding of the nature and mechanisms of angle closure is needed to improve outcomes. The Singapore-Swiss Narrow Angle Study will compare the prevalence of Swiss and Singaporean angle closure to describe the natural history of the disease and characterize the underlying mechanism of angle closure and the difference in treatment response of each group. The same cohort and additional patients will then be included in a longitudinal study for a minimum of 3 years.

“Preliminary [ultrasound biomicroscopy] findings have shown that in both the Singapore and Swiss cohorts, angle closure is more often caused by a combined mechanism, — 72% and 55%, respectively — than by a single mechanism,” Chew said. “Pupillary block, alone or in combination with lens or iris-related factors, is the most common cause. Iridotomy does eliminate pupillary block, but is not always effective.” – by Michela Cimberle

References:

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For more information:

Paul Chew, MD, can be reached at the Department of Ophthalmology, Yong Loo Lin School of Medicine, National University of Singapore, 5 Lower Kent Ridge Road, Singapore 119074; email: pcglaucoma@gmail.com.
Disclosure: Chew has no relevant financial disclosures.