Asians fare worse after treatment for angle-closure, study says

Long-term sequelae were different in Asians compared with white patients. Peripheral iridotomy appeared less effective in maintaining IOP control.

Issue: April 1, 2001

SINGAPORE — There is a markedly different course for Asian patients treated for acute angle-closure compared with white patients, a retrospective comparative study found. A high proportion of Asian eyes with acute primary angle closure developed an increase in intraocular pressure (IOP) on long-term follow-up, the study found. A literature review found that white patients had better results.

First author Tin Aung, FRCS, FRCOphth, and colleagues reviewed the charts of consecutive patients who presented for care after suffering attacks of acute angle-closure glaucoma between 1990 and 1994 at the National University Hospital here.

Response to LPI

After review of 96 patient charts (111 eyes), the investigators determined that 64 eyes (58%) failed to respond adequately to laser peripheral iridotomy (LPI) alone, and more than one-third would eventually require trabeculectomy. IOP would become elevated in 49 of 64 eyes (76%) within 6 months or less.

Patient age ranged from 39 to 94, (mean age 63.7). Most were female. Presenting IOP ranged from 28 mm to 80 mm Hg with a mean of 52.8. Fifteen percent of patients had bilateral involvement. All except one eye received patent sequential argon-Nd:YAG laser iridotomies resulting in arrest of the acute angle-closure emergency. IOP in all eyes was reduced below 21 mm Hg in the immediate post-treatment period.

Singapore is alleged to have the greatest incidence of acute angle-closure glaucoma of any country studied, the authors note. In east Asia, primary acute angle-closure glaucoma is a major form of glaucoma, compared to Europe and North America, and the high incidence of angle-closure in Singapore makes it ideal for the long-term study of the outcome for the disease after different treatment modalities,” the paper says.

LPI and medications

LPI, even when combined with medical therapy, seemed to confer a different benefit to Asian patients versus British subjects, according to the study.

“In this series of Asian eyes with acute primary angle-closure, only 41.8% of eyes with acute primary angle-closure were successfully treated with laser peripheral iridotomy alone, and did not develop a subsequent increase in IOP on follow-up after resolution of the acute episode,” the authors said.

A randomized controlled study in the United Kingdom, however, showed “IOP control without further treatment in 70.4% of eyes after laser iridotomy.”

When the response to LPI was suboptimal, the addition of ocular anti-hypertensive medication seemed to again affect the two groups differently. In white patients, “if additional medication was used, IOP control was achieved in 84% to 99% of eyes, contrasted with 65% of east Asians receiving additional medication to control IOP,” the study said.

Elevated IOP despite patency

Almost 76% of the Asian eyes that exhibited increased IOP (greater than 21 mm Hg) after LPI alone did so within 6 months or less. Thirty-six eyes had elevated IOP “very early within the first month,” they reported.

“The mechanism of progression from acute into chronic angle-closure is not yet well understood,” Dr. Aung told Ocular Surgery News.

These findings “emphasize the need to monitor IOP closely in the first few months after acute primary angle-closure in order to detect any subsequent increase in IOP early,” Dr. Aung said.

The patient is likely to be asymptomatic and maintain a patent iridotomy despite elevated IOP, he said.

“These patients with a very early increase in IOP could possibly have had subacute angle-closure or an underlying chronic angle-closure that went unnoticed until the acute attack for which the patient sought an ophthalmic solution,” the report said.

Sharp contrasts

“The findings of this study thus contrast sharply with those of non-Asians,” the authors determined.

“It seems that in Asian patients, laser peripheral iridotomy alone is not able to prevent the majority of eyes from developing a clinically significant increase in IOP on follow-up after acute primary angle-closure. Many eyes also tend to become medically uncontrollable in a very short period of time after the acute episode, and filtering surgery (trabeculectomy) was required in 36 eyes ( 32.7%). In contrast, only 1% to 13% of eyes were reported to eventually require filtering surgery in studies in Caucasians,” the report said.

“Many Asian patients may have further glaucomatous visual damage if this trend is not detected,” the authors continue, “This is a serious problem that merits further research and attention because it is a potential cause of blindness affecting a large proportion of the world’s population.”

Other factors

The study suggests several factors that could explain why acute angle-closure seems more refractory to treatment in east Asians, including genetic and anatomic predisposition. Asian eyes may be more prone to formation of peripheral anterior synechiae than eyes of other races, leading to chronic or creeping angle-closure, according to the study.

Noting that the length of symptoms averaged 6.5 days, the authors said they believe the closure attacks are longer and more debilitating than in other groups, with more damage to aqueous outflow mechanisms affecting long-term prognosis.

“Such severe attacks of acute primary angle-closure may cause angle damage resulting in diminished outflow and increased IOP weeks to months later,” the authors said.

Additionally, the irides of east Asians might be a factor. “Chinese eyes have thick dark-brown irides, and laser peripheral iridotomy in such eyes require much more laser energy to penetrate the iris. It is possible that the inflammation and pigment release from doing the laser peripheral iridotomy in such eyes could also have worsened the trabecular damage and contributed to the subsequent failure of IOP control,” the report said.

LPI, the study authors noted, helped break the acute attack and prevented further acute angle-closure emergencies in all patients.

For Your Information:

Tin Aung, FRCS, FRCOphth, can be reached at Flat 15, Boddoington House, 40, Trinity Church Rd., Barnes, London SW13 8 EB England; fax: (44) 208-7486272; e-mail: tin11pacific.net.sg.

Reference:

Aung T, Ang LP, et al. Acute primary angle-closure: Long-term intraocular pressure outcome in Asian eyes. Am J Ophthalmol. 2001;131:7-12.