Prediction of Behind-Iris Structures by Use of Anterior Segment Optical Coherence Tomography Parameters

Abstract

Purpose: To evaluate whether the ultrasound biomicroscopy (UBM) parameters associated with structures behind iris can be induced using anterior segment optical coherence tomography (AS OCT) parameters in patients with primary angle closure (PAC). Study design: Retrospective, observational study Subjects: A total of 106 eyes of 106 PAC patients Methods: PAC eyes were imaged using both UBM and AS OCT under the same lighting conditions. Anterior chamber depth, anterior chamber area, lens vault, iris cross-sectional area, iris curvature, iris thickness at 750μm form the scleral spur (SS), angle-opening distance at 750μm anterior to SS, angel recess area at 750μm anterior to SS, trabecular iris space area at 750μm anterior to SS, and pupil diameter were estimated on AS OCT image; trabecular-ciliary process angle, trabecular-ciliary process distance, iris-ciliary process distance, ciliary body thickness 1mm posterior to SS were measured on UBM image using ImageJ software. UBM images were categorized into one of three angle closure mechanisms; pupillary block (PB), plateau iris configuration (PIC), and iridolenticular wrapping (WR). Outcome measure: Uni- and multivariate linear regression analysis were used for prediction of UBM parameters. Subgroup comparison was done with Kruskal-Wallis test, χ2-test and Mann-Whitney test. Results: Forty-nine eyes were categorized into PB group, 28 eyes into PIC group, and 29 eyes into WR group. In multivariate linear regression, LV, IC and IA were major parameters to predict behind-iris structure. Coefficients of determination of multivariate linear regression analysis for UBM parameter were 3.9~28.3%. PB group showed larger IC compared with the other groups. AOD750 in PIC group was longer than those in the other groups, and WR group had smaller ACD and larger LV compared with the other groups. Conclusions: AS OCT parameters alone are insufficient to predict and explain the UBM parameters. However, some AS OCT parameters are associated with subclassification using UBM images showing behind-iris structures, thus angle closure mechanism classification can be done by assist of AS OCT parameters.