Purpose: To assess the intraobserver and interobserver variability of new software for the analysis of anterior chamber-angle images obtained using ultrasound biomicroscopy (UBM).
Patients and methods: Consecutive UBM images of 4 quadrants (the superior, the nasal, the temporal, and the inferior) of 30 primary angle-closure suspects (PACSs) and 30 normal subjects with open angles were selected. Two observers used the new UBM image analysis software to calculate the following parameters on 2 separate occasions: angle opening distance (AOD), trabecular-iris angle (TIA), angle recess area (ARA), trabecular-ciliary process distance (TCPD), iris-ciliary process distance (ICPD), and iris thickness (IT). Intraobserver and interobserver reproducibility were measured using intraclass correlation coefficient (ICC) and Bland-Altman plots.
Results: For intraobserver measurements in PACS, the range of ICC for AODs, TIAs, ARAs, TCPDs, ICPDs, and ITs in the 4 quadrants were 0.77 to 0.94, 0.80 to 0.92, 0.82 to 0.94, 0.51 to 0.73, 0.42 to 0.78, and 0.76 to 0.89; in open angles, these were 0.83 to 0.94, 0.80 to 0.93, 0.84 to 0.93, 0.57 to 0.89, 0.57 to 0.84, and 0.70 to 0.95. For interobserver measurements in PACS, the range of ICC for AODs, TIAs, ARAs, TCPDs, ICPDs, and ITs in the same quadrants as above were 0.52 to 0.89, 0.65 to 0.92, 0.68 to 0.92, 0.22 to 0.80, 0.48 to 0.93, and 0.29 to 0.75; in open angles, these were 0.57 to 0.87, 0.60 to 0.86, 0.64 to 0.90, 0.27 to 0.94, 0.56 to 0.93, and 0.28 to 0.66.
Conclusions: Angle width (AOD, TIA, and ARA) and IT of both PACS and open angles could be reliably measured by the same observer; interobserver measurements and those related to the ciliary process (TCPD and ICPD) were more variable. For the current version of this software, we recommend measurements of anterior chamber parameters by the same observer.