Primary angle closure glaucoma (PACG) is a significant concern, especially for Asian populations who are at a much higher risk. This was the key theme at an engaging plenary session on Day 3 of the 7th Congress of the Asia-Pacific Glaucoma Society (APGC 2024) in Manila, Philippines. During the session, angle closure specialists explored the anatomical peculiarities, risk factors and treatment options tailored to the Asia-Pacific demographic.
The anterior segment and Asians
Dr. Shan Lin from the Glaucoma Center of San Francisco (USA) shared some intriguing insights into anterior segment findings among Asians, shedding light on why angle-closure glaucoma (ACG) is more prevalent among Asian populations.
“Asians have more glaucoma, particularly angle-closure glaucoma, and we’re exploring why that is,” Dr. Lin noted, humorously prefacing his presentation with, “The only relevant disclosure here is that I’m Asian.”
He explained that anterior chamber depth and width are generally smaller in Asians compared to Caucasians, leading to a more crowded anterior segment and increased ACG risk. “When we looked at the anterior chamber volume and its area, it was smaller in Chinese,” he said. Additionally, the iris thickens more in the dark in the Chinese population, further narrowing the angle.1,2
Different Asian subgroups show unique anatomical features. For instance, the Japanese have a slightly larger anterior chamber width, which offers some protection, while Koreans and Filipinos show higher risk traits but also have protective factors like smaller lens vaults.3,4,5
“A narrow angle, thicker iris, and greater curvature of the iris are common in the Filipino population, but their smaller lens vault may be protective,” Dr. Lin explained.
PACS progression
Dr. Tin Aung from the Singapore National Eye Centre (SNEC) discussed managing primary angle closure suspects (PACS), drawing insights from the ZAP and ANA-LIS trials. Reflecting on research data from the two studies, Dr. Aung emphasized the low risk of PACS progression.6,7
“The prevalence of angle closure suspects is much higher than angle closure glaucoma, suggesting that most won’t progress,” Dr. Aung highlighted.
“Observation remains a viable option, especially for patients with minimal cataracts,” he added, but cautioned against complacency, likening it to Singapore’s low crime rate. “Low risk doesn’t mean no risk,” Dr. Aung emphasized, urging patients to understand the nuances before deciding.
The trials underscored the importance of informed decision-making. “We discuss with the patient the options of observation versus laser peripheral iridotomy, quoting the data on progression incidence,” Dr. Aung explained. He also acknowledged cultural variations, citing London’s practice of discharging most PACS patients without laser intervention.
PACS risk assessment
Dr. Benjamin Xu from the University of Southern California (USA) provided insights into PACS risk stratification and the role of ocular biometrics. Despite its global prevalence, with three-quarters of cases occurring in Asia, PACS poses challenges in management and risk assessment.
Drawing from longitudinal studies like the aforementioned ZAP trial, Dr. Xu highlighted the limited progression rate of untreated PACS, suggesting that laser peripheral iridotomy may not be the most efficient use of resources. Instead, he emphasized identifying high-risk PACS eyes that warrant earlier intervention.
Patient history emerged as a valuable tool for risk assessment, with familial predisposition and older age being significant factors. Dr. Xu also explored the potential of ocular biometrics, particularly anterior segment OCT (AS-OCT), in predicting angle closure severity and progression.
“AS-OCT produces beautifully high-resolution images,” said Dr. Xu. “We can quantitatively analyze AS-OCT images and derive measurements of biometric parameters that describe the size, shape and configuration of the anatomical structures at the front of the eye.”
AS-OCT offers quantitative insights into anatomical structures, aiding in identifying eyes at higher risk. “AS-OCT imaging provides us with information that is not available using gonioscopy,” he stated, highlighting its significance in evaluating PACS.
Looking ahead, Dr. Xu outlined the need for longitudinal studies in diverse populations to refine risk assessment strategies. The ongoing Multiracial Angle Closure Progression Study (MAPS) aims to address these gaps by establishing OCT-based definitions of narrow angles and monitoring high-risk patients over time.
When lens extraction is not enough
When faced with PACG, deciding between phacoemulsification (phaco) alone or combining it with trabeculectomy (phaco-trab) can feel like choosing between a latte and a double espresso—both serve their purpose, but one packs a stronger punch. Dr. Clement Tham from The Chinese University of Hong Kong discussed when lens extraction alone is enough.
According to Dr. Tham, if you need only a modest drop in IOP, phaco might just do the trick. “If you only require a relatively small amount of IOP reduction, then probably lens extraction alone would be sufficient,” he explained.
If you’re aiming for a dramatic decrease in IOP, adding trabeculectomy to the mix might be necessary. “If you need dramatic, substantial IOP reduction, then you probably need to add something else,” Dr. Tham advised.
So, while phacoemulsification can be a straightforward solution for mild cases, phacotrabeculectomy might be the go-to for those needing maximum pressure relief. And for those in the middle, a study by Dr. Isabelle Lai (Hong Kong) found that phaco-ECP offers a balanced approach with moderate IOP reduction and very few additional risks.8
Ultimately, the best choice depends on various factors like the preoperative IOP, the number of medications the patient is on, the stage of glaucoma, and the patient’s overall health and preferences. As Dr. Tham put it, “It is very important that you sit down with your patient and go through the pros, cons and risks of each individual surgical option.”
Managing refractory PACG
Dr. Paul Healey from the University of Sydney in Australia shared strategies for managing refractory PACG, a condition where angle-closure glaucoma persists despite attempted interventions. “Refractory PACG occurs when primary angle closure persists after angle rehabilitation measures have failed,” he explained.
To target a very high IOP and dysfunctional trabecular meshwork, Dr. Healey suggested medical therapy as well as promising new treatments like laser trabeculoplasty and intraocular stents.
Editor’s Note: Reporting for this event took place during the 7th Congress of the Asia-Pacific Glaucoma Society (APGC 2024), held from May 24-26, 2024 in Manila, Philippines.
References
- Wang D, Huang G, He M, et al. Comparison of anterior ocular segment biometry features and related factors among American Caucasians, American Chinese and mainland Chinese.Clin Exp Ophthalmol. 2012;40(6):542-549.
- Wang D, He M, Wu L, et al. Dark-light change of iris parameters and related factors among American Caucasians, American Chinese, and mainland Chinese. Curr Eye Res. 2012;37:599-605.
- Pekmezci M, Vo B, Lim AK, et al. The characteristics of glaucoma in Japanese Americans. Arch Ophthalmol. 2009;127(2):167-171.
- Kang JM, Baek SU, Chansangpetch S, et al. Comparison of anterior segment parameters among Koreans, Chinese, and White persons. Ophthalmol Glaucoma. 2018;1(3):182-188.
- Sales CS, Lee RY, Agadzi AK, et al. Open-angle glaucoma in Filipino and white Americans: a comparative study. J Glaucoma. 2014;23(4):246-253.
- He M, Jiang Y, Huang S, et al. Laser peripheral iridotomy for the prevention of angle closure: A single-centre, randomised controlled trial. Lancet. 2019;393(10181):1609-1618.
- Baskaran M, Kumar RS, Friedman DS, et al. The Singapore asymptomatic narrow angles laser iridotomy study five-year results of a randomized controlled trial. Ophthalmology. 2022;129(2):147-158.
- Lai ISW, Chan NCY, Ling A, et al. Combined phacoemulsification-endoscopic cyclophotocoagulation versus phacoemulsification alone in primary angle-closure glaucoma: A pilot randomized controlled trial. Ophthalmol Glaucoma. 2021;4(6):589-596.
