Jiang, Y; (2015) Changes in Anterior Segment Configuration in Primary Angle-closure Suspects after Prophylactic Laser Iridotomy. Doctoral thesis , UCL (University College London).

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Text Yuzhen Jiang PhD Thesis--finalised-UCL Institute of Opthalmology.pdf Download (3MB) | Preview

Abstract

Aims To determine the immediate and longitudinal changes in anatomical configurations of the anterior chamber angle in primary angle-closure suspects eyes treated and untreated by laser peripheral iridotomy (LPI). This research project also aims at investigating associations of angle configuration, dynamic iris behaviours and factors associated with outcomes of prophylactic LPI in primary angle-closure (PAC) suspects. Methods Study subjects were participants in a prospective randomised controlled clinical trial. Each participant was treated by LPI in one randomly selected eye, with the fellow eye serving as a control. Angle configuration and iris configuration were assessed in a masked fashion using gonioscopy and anterior segment optical coherence tomography (AS-OCT) before and at 2 weeks, 6 months, 18 months, 36 months and 54 months after LPI. Anatomical features of angle-related structures were assessed with a qualitative grading system using standard ultrasound biomicroscopy (UBM) images. Results Of the 889 PAC suspects who were included into the current study, 735 were women. At baseline, compared to males, female participants appeared to have narrower gonioscopic angle width, wider range of appositional iridotrabecular contact, narrower limbal anterior chamber depth. In most of the eyes of primary angle-closure suspects in the current study, gonioscopic angle width measured in four quadrants followed the same sequence, namely: inferior > nasal > temporal > superior. Compared to eyes with wide open angles after LPI, a greater proportion of eyes with angles which remained narrow after LPI had medium or thick overall iris thickness (P values≤0.009). Relatively more eyes with angles which remained narrow after LPI had anterior iris insertion, especially in the superior quadrant (P<0.001). Eyes with residual narrowing of angles after LPI also tended to have anteriorly positioned ciliary process (P values≤ 0.002). No significant difference was found in baseline measures of angle configuration between treated and untreated eyes. At 2 weeks after LPI, the drainage angle on gonioscopy widened from a mean of 13.3⁰ at baseline to a mean of 25.5⁰ in treated eyes, which was also confirmed by significant increases in all AS-OCT angle width measures(P<0.001 for all variables). Between 2 weeks and 18 months following LPI, a significant decrease in angle width was observed over time in treated eyes (P<0.001 for all variables), although the change over the first 5.5 months was not statistically significant. In untreated eyes, angle width consistently decreased across all follow-up visits after LPI, with a more significant longitudinal trend for narrowing of angle configuration compared to treated eyes. In men and women, both treated and untreated eyes experienced a slight but statistically significant increase at 36 months after LPI, and then decreased once again with time toward 54 months after LPI. At baseline, in both men and women the cross-sectional area and volume of the iris significantly decreased when the illumination changed from light to dark (all differences were statistically significant, P<0.001). Two weeks after LPI, the relationship between iris cross-sectional area in dark and in light remained similar, although the magnitude of dynamic change in iris anatomy decreased significantly compared to the pre-LPI status. Conclusions Eyes with thicker overall or peripheral iris, more anterior insertion of the iris, and more anteriorly positioned ciliary body are more disposed to having persistent narrow angles following LPI. LPI resulted in remarkable increase in angle width of PAC suspects immediately after the procedure. However, this did not seem to change the trend for anterior chamber angle to narrow down over time, which was shown in our study cohort to be a shared feature in both treated and untreated eyes. The current research has also shown that decrease in illumination can result in significantly decreased iris cross-sectional areas in eyes of PAC suspects. This characteristic of iris dynamic behaviour in PAC suspects was compromised by the elimination of pupillary block in female angle-closure suspects.

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