This randomized controlled trial, also known as the Zhongshan Angle Closure Prevention (ZAP) trial, evaluated the efficacy of prophylactic laser peripheral iridotomy (LPI) in bilateral angle-closure suspects.
Study design
Patients aged 50 to 70 years old residing in urban China were screened to identify bilateral primary angle-closure suspects (PACS). Eligible patients had an appositional closure of 180° or greater on gonioscopy in the absence of elevated IOP, peripheral anterior synechiae (PAS) or glaucomatous damage.
Eight-hundred and eighty-nine eligible patients were randomized to receive laser iridotomy in 1 eye, while the other eye remained an untreated control. Patients were followed for 72 months. The primary outcome of primary angle closure (PAC) was defined as IOP greater than 24 mm Hg on 2 occasions, development of at least 1 clock-hour of PAS or an episode of acute angle closure.
Outcomes
Overall, PAC occurred in 4.19 per 1,000 eye-years in treated eyes and in 7.97 per 1,000 eye-years in untreated eyes (P=0.024). The primary outcome occurred in 19 treated and 36 untreated eyes during 72 months of follow-up (P=0.0041), mostly due to development of PAS. Of note, the incidence of the primary outcome was much lower than anticipated.
Limitations
One important exclusion criterion in this study was an IOP spike of greater than 15 mm Hg post-dilation or after a 15-minute dark room provocation test; this form of testing is not routinely done in clinical practice and may have excluded patients with a high likelihood of achieving the primary outcome. IOP measurements were completed using non-contact tonometry, and were only confirmed with applanation if IOP was greater than 24 mm Hg—thereby potentially missing cases in which IOP was erroneously measured below 24 mm Hg. This study was limited to Chinese patients, an ethnicity that has a high incidence of primary angle closure and may not be representative of other ethnicities.
Clinical significance
The risk of converting from PACS to PAC was low during this 6-year study in Chinese patients. Laser iridotomy decreases the risk of this conversion, although the incidence of PAC is remarkably low. This study suggests that perhaps laser iridotomy is not required in all angle-closure suspects, especially if they mirror the demographics of this study population.