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Editors Selection IGR 24-3

Surgical treatment: Angle closure after peripheral iridotomy

Comment by Minguang He on:

13071 Prevalence and mechanism of appositional angle closure in acute primary angle closure after iridotomy, Yeung BY; Ng PW; Chiu TY et al., Clinical and Experimental Ophthalmology, 2005; 33: 478-482

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Yeung et al. (971) reported a high proportion rate of appositional closure in acute primary angle closure (APAC, 18 eyes) and their fellow eyes (14 eyes) even after a patent laser peripheral iridotomy (LPI). This finding was then used to explain the high positive rate of provocative test among the iridectomized eyes found in Chinese. Based on the comparison of UBM quantitative measurement between the APAC eyes and normal controls, the authors proposed the anteriorly positioned ciliary body as a possible mechanism of appositional closure in APAC after LPI. However, the study may be subject to methodological problems. The appositional closure was not correctly defined. Appositional closure should be a reversible temporary contact between peripheral iris and trabecular meshwork, it can be suggested by 'static' gonioscopy without indentation and may be better to confirm by UBM in the dark. The authors defined this as "closed angle, Schwalbe's line not visible or only Schwalbe's line visible," using Posner indentation gonioscopy. The authors also used the visible angle structure that occupied more than 180 degree of circumference to represent the eye. Those eyes with this characteristic could be synechial closure (in fact, the authors reported 10 out of 18 APAC eyes had 90 to 180 degree of PAS), hence, the peripheral iris obscuring the visibility of trabecular meshwork alone in gonioscopy does not imply appositional closure. The UBM comparison of APAC or fellow eyes with normal controls is also problematic - this comparison is only valid to interpret the anatomical basis of narrow angle but not the mechanism of high rate of appositional closure after iridotomy. To correctly interpret this, the authors should compare the UBM

After peripheral iridotomy a high rate of appositional angle closure was seen

findings in the eyes with appositional closure with those without after LPI. In fact, based on the UBM figures 2 and 3 presented in the result section, anterior iris insertion and thick peripheral iris are determining factors for post-iridotomy angle closure but not anteriorly located ciliary body because ciliary sulcus apparently exists. The high rate of appositional closure in the fellow eyes is a real interesting finding because it suggests a large number of angles remaining close in the eyes with high risk but without acute episode even after LPI. Finally, an anatomically appositional closure after LPI does not exclusively imply a failure of LPI in the controls of IOP, this will require a prospective well-designed study (including a trial), and need to enrol much more APAC patients with sufficient variation on disease severity and staging.

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