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Y. Yang, J. Zhao, Q. Zhou, J. Mao, R. Sui, X. W. Liu, Y. Zhang, R. Jiang, X. L. Liu; The Prevalence and Pathogenesis of Angle Closure in Eyes With Primary Angle Closure After Laser Peripheral Iridotomy. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2464.
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Primary angle closure (PAC) is thought to be caused by pupillary block. Since laser peripheral iridotomy (LPI) can eliminate pupillary block, it is widely used as an early intervention for PAC. However, some cases were intractable. In this study, we used ultrasound biomicroscopy (UBM) to evaluate the prevalence of angle closure in eyes with PAC after LPI and determine the pathogenesis of this condition.
(1) Prophylactic LPI was performed in 45 patients with appositional PAC (Plateau iris was excluded). UBM examination was carried out before and 2 weeks after LPI in these eyes at 8 different clock positions radially. 1 randomly selected eye of each subject was measured. UBM parameters before LPI were compared with those after LPI, including central anterior chamber depth (ACD), iridotrabecular contact (ITC), iris-ciliary process contact (ICPC), angle opening distance (AOD), trabecular-ciliary process distance (TCPD), iris distance (ID), scleral spur-ciliary process distance (SSCPD) and trabecular-ciliary process angle (TCPA). (2) The PAC eyes were classified into two groups according to the severity of angle closure after LPI, severe ( ≥4 clock positions, 27 eyes) and mild ( ≤3 clock positions, 18 eyes). UBM parameters of the PAC groups after LPI were compared with the group with normal anterior chamber depth (20 eyes), including ACD, ID, TCPD, TCPA, SSCPD.
(1) 82% (37/45) PAC eyes had wider angles after LPI . However, the proportion of eyes with UBM-identified ITC in ≥1 clock position after LPI was 87% (39/45). (2) TCPD and TCPA were significantly smaller in the severe angle closure group compared to the mild angle closure group as well as the normal group (P=0.0001). ACD was significantly smaller in PAC eyes than normal ones (P<0.0001), however, there was no significant difference in ACD within the PAC groups (P=0.7170). There were no significant differences among the three groups in ID and SSCPD (P>0.05). The correlation coefficient between angle closure range and TCPD, TCPA after LPI were -0.4291 (P=0.0037) and -0.3785 (P=0.0103) respectively.
Our study showed that angle closures were still present in most of the PAC eyes after LPI, due to the anteriorly positioned ciliary processes which held peripheral iris from going backwards after LPI. Peripheral iris thickness did not show significant correlation with angle closure. It suggested that anteriorly positioned ciliary processes might be another important factor in the pathogenesis of PAC in some Asian eyes besides pupillary block.
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