Musings of a Prospective Angle Closure Patient

My interest in angle closure disease is both professional and personal. As an Asian woman with a strong family history of glaucoma – my mother had bilateral acute primary angle closure (APAC) and my father is a primary angle closure suspect (PACS) – irido-trabecular contact seems written into my genetic code. When I first embarked on my residency 15 years ago, laser peripheral iridotomy (LPI) was regarded as the “gold standard” treatment for angle closure disease, even in the absence of glaucoma or raised IOP (1). Surveys show that 84.9 percent of ophthalmologists in Singapore (2) and 75 percent in the United Kingdom would advise LPI for asymptomatic PACS (3).

Though I had resigned myself to undergoing LPI at some point in my life, truthfully, I have never been a fan of the laser procedure. The efficacy and safety of prophylactic LPI has not been well established, and LPI has been associated with corneal decompensation, linear photopsia and raised IOP (1). In addition, LPI only eliminates pupil block, leaving other mechanisms unaddressed.

It is for this reason I welcome the findings of the Zhongshan Angle Closure Prevention (ZAP) Trial, which showed that, even with observation, the incidence of angle closure disease was very low among individuals classified as PACS (<1 percent per year). As the prophylactic effect of LPI was modest (albeit significant), widespread prophylactic LPI for asymptomatic PACS was not recommended on a population basis (4).

Even in the presence of raised IOP and/or glaucomatous optic neuropathy, LPI is no longer considered the treatment of choice. In the EAGLE trial, clear-lens extraction showed greater efficacy and was significantly more cost-effective than LPI. Significantly fewer participants in the clear-lens extraction group required any treatment to control IOP and the mean number of glaucoma medications required at 36 months was significantly lower compared with the LPI group (0.4±0.8 vs 1.3±1.0, p<0.0001). The frequency of complications associated with clear-lens extraction was low, though this may be because the surgeries were performed by experienced surgeons who had completed training in both general ophthalmology and glaucoma (5).

Comparing phacoemulsification alone with combined phacotrabeculectomy in the treatment of medically controlled primary angle closure glaucoma (PACG) with coexisting cataract, the combined procedure has been shown to reduce the requirement for topical glaucoma medications, but was associated with more complications and additional surgery in the postoperative period (6). MIGS procedures may have a role in reducing the glaucoma medication burden in PACG eyes, with reduced complications compared with trabeculectomy.

In an exploratory study, we have shown that combined iStent implantation with cataract surgery was effective in lowering the IOP and the number of glaucoma medications in eyes with primary angle closure disease for at least 12 months, with a favorable safety profile (7). Further randomized trials are required to determine the additional benefit of MIGS in PACG eyes undergoing cataract surgery.

A limitation of most studies, including the ZAP and EAGLE trials, is the exclusion of anterior segment imaging in the protocol, making it impossible to determine the mechanisms of angle closure. It is well established that PACG is a heterogenous disease with various mechanisms, including pupil block, bulky lens, plateau iris and thick peripheral iris roll. If a large proportion of study participants had bulky lenses, the results would likely favor lens extraction over LPI. These findings are unlikely to be applicable to eyes with a significantly convex iris configuration and minimal lens vault, which indicate a predominantly pupil block mechanism.

In the age of personalized medicine, I hope that angle closure treatment will evolve to address the specific anatomical characteristics and mechanism of each patient. Using pre-treatment anterior segment OCT scans, we have developed an algorithm that predicts the efficacy of LPI in PACS eyes, with predictive accuracy that is superior to fellowship-trained ophthalmologists (8). For personalized treatment to become a reality, further research into mechanism-specific treatment is required. And when I finally develop angle closure in the not-too-distant future, I certainly hope for management bespoke to my anterior segment anatomy.