The reproducibility of mechanism categories of angle closure using ultrasound biomicroscopy and anterior segment optical coherence tomography

Abstract

Background Angle closure is the pathological basis of primary angle-closure disease (PACD). Understanding different types of angle closure mechanisms is significant for evaluation of risk factors, prevention, diagnosis and treatment of PACD.Ultrasound biomicroscopy (UBM) is commonly used for investigating the types of angle closure mechanisms in clinical works.However, UBM is a contact examination, which limits its application.Anterior segment optical coherence tomography (AS-OCT) is a non-contact examination of segment imaging, through which qualitative and quantitative evaluations of the chamber angle can be made. Objective This study was to investigate the reproducibility of mechanism categories of angle closure based on AS-OCT images and UBM images. Methods Cross-sectional study was performed.PACD outpatients from September to October in 2013 in Beijing Tongren Hospital were enrolled and received both UBM and AS-OCT examinations.UBM images were obtained in superior, inferior, nasal and temporal quadrants of the chamber.AS-OCT images were obtained in the anterior segment quadrant mode at 0-180, 45-225, 90-270, and 135-315 degree meridians.UBM and AS-OCT images were categorized into three dominant angle closure mechanisms: pupil block, located ciliary body and thick peripheral iris roll, separately.And the same mechanism of at least two UBM/AS-OCT images of one eye was defined as the angle closure mechanism of this eye.If both eyes of one PACD patient were eligible for inclusion, the right eye was selected for analysis.The reproducibility of two examinations was evaluated by Kappa coefficients. Results Finally 40 PACD patients (40 eyes, 27 right eyes and 13 left eyes) were enrolled for analysis.Based on UBM images, 12 eyes (30.0%) were classified as pupil block, 23 eyes (57.5%) as located ciliary body and 5 eyes (12.5%) as thick peripheral iris roll.Based on AS-OCT, 12 eyes (30.0%) were classified as pupil block, 21 eyes (52.5%) as located ciliary body and 7 eyes (17.5%) as thick peripheral iris roll.The Kappa coefficient for the classification of angle closure mechanisms was 0.870. Conclusions Criterion of angle closure mechanism categories based on AS-OCT images was established.Mechanism categories obtained from AS-OCT and UBM images showed a good reproducibility. Key words: Angle closure mechanism; Anterior segment optical coherence tomography; Ultrasound biomicroscopy; Reproducibility