Quantitative Evaluation of Iris Convexity in Primary Angle Closure

Purpose In eyes with primary angle closure (PAC), we quantitatively evaluated anterior bowing of the iris by means of ultrasound biomicroscopy (UBM). Design Retrospective, observational, and consecutive case series. Methods A total of 203 phakic eyes with PAC that had not undergone any surgical or laser treatment were included. Using UBM, we measured anterior chamber depth (ACD) and iris convexity (IC): the maximum distance from the posterior surface of the iris to the iris plane passing through the pupillary margin of the iris and iris root. Results The average IC was 0.22 ± 0.1 mm, although there was considerable individual variation. The IC value was correlated weakly, albeit significantly, with age ( r = 0.22, P < .01), and strongly with ACD ( r = −0.57, P < .0001). Conclusions In eyes with PAC, older age and a more shallow ACD appear to be important causes of increased forward bowing of the iris resulting from pupillary block.