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Editors Selection IGR 16-3

Anatomical structures: Angle configuration changes

Comment by Noel Chan on:

58618 Longitudinal changes of angle configuration in primary angle-closure suspects: the Zhongshan Angle-Closure Prevention Trial, Jiang Y; Chang DS; Zhu H et al., Ophthalmology, 2014; 121: 1699-1705

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Laser peripheral iridotomy (LPI) is considered a standard treatment in acute or chronic angle closure glaucoma.¹ However, without prior history of primary angle closure (PAC), the benefit of LPI in asymptomatic eyes with narrow angles has been inconclusive. The Zhongshan Angle-Closure Prevention trial was initiated in 2008 to shed light in this area and hopefully help guide future management of primary angle closure suspects (PACS). In this longitudinal cohort of 775 PACS subjects, one eye of each participant was randomized to receive LPI while the fellow eye remained untreated and served as a control. Changes in angle configuration between the two eyes were compared at two weeks, six months and 18 months after LPI using gonioscopy and anterior segment optical coherence tomography (AS-OCT). This was a well-conducted study with strengths including large sample size, randomization, uniform cohort, control with fellow eye and reasonable follow-up duration. The use of ASOCT for angle assessment also ensured more objective and reproducible measurements.

"This [study] has provided further evidence to the existing theory that non-pupil block mechanisms play a considerable role in causing PAC."

Two weeks after LPI, treated eyes were found to have a wider drainage angle than control eyes or baseline. Together with a significant reduction in iris curvature, the results further proved the effect of LPI in eliminating pupil block mechanism. This result was expected and consistent across existing literature.^2-4 However, six months after LPI, the angle width decreased over time in all treated eyes while the untreated eyes experienced a decrease in angle width in a more rapid fashion (1.2°/year versus 1.6°/ year). This has provided further evidence to the existing theory that non-pupil block mechanisms play a considerable role in causing PAC.⁵ Not surprisingly, 25% of treated eyes in this study were found to have persistent angle closure despite successful iridotomies. One of the interesting results from this study was a significant increase in AS-OCT angle width in both treated and untreated eyes at two weeks post-LPI. Despite the postulated explanation of systemic absorption of pilocarpine administered prior to laser, there was no significant difference in pupil diameter observed before and two weeks after LPI in both groups. Another interesting finding was that, compared with controls, treated eyes had significantly greater lens vault at 18 months post-LPI. The authors suggested that apart from aging, LPI might have additional effect on the crystalline lens, especially the contour of its anterior surface. Although the study has demonstrated beneficial effect of LPI in angle widening in PACS eyes, some of these interesting results were yet to be answered. I look forward to the authors' follow-up studies investigating any difference in the development of PACG between the two eyes.

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