Anterior chamber angle imaging with swept-source optical coherence tomography: comparison between CASIAII and ANTERION

Abstract

This study compared the test-retest variabilities and measurement agreement of anterior chamber angle (ACA) dimensions measured by two anterior segment swept-source optical coherence tomography (SS-OCT)-the ANTERION (Heidelberg Engineering, Heidelberg, Germany) and CASIAII (Tomey, Nagoya, Japan). Thirty-eight subjects, 18 patients with primary angle closure and 20 healthy participants with open angles, were included. The mean age was 54.7 ± 15.8 years (range: 26-75 years). One eye of each subject was randomly selected for anterior segment imaging by ANTERION and CASIAII, using the same scan pattern (6 evenly spaced radial scans across the anterior segment for three times) in the same visit. The between- and within-instrument agreement and repeatability coefficients of angle open distance (AOD500), trabecular-iris space area (TISA500), lens vault (LV), scleral spur-scleral spur distance (SSD), anterior chamber depth (ACD), and pupil diameter (PD) were measured. The anterior and posterior boundaries of the cornea, iris, and lens were automatically segmented by the SS-OCT instruments; the scleral spur was manually located by a single masked observer. There were significant differences between ANTERION and CASIAII measurements; the SSD, PD, and ACD were smaller whereas AOD500 and TISA500 were greater in ANTERION compared with CASIAII (P < 0.001). Anterior segment measurements obtained from the two SS-OCT instruments showed strong associations (R² ranged between 0.866 and 0.998) although the between-instrument agreement was poor; the spans of 95% limits of between-instrument agreement were ≥ 1.5-folds than the within-instrument agreement for either instrument. Whereas both SS-OCT instruments showed low test-retest measurement variabilities, the repeatability coefficients of AOD500, TISA500, ACD, and PD were slightly smaller for CASIAII than ANTERION (P ≤ 0.012).

Figure 1

Bland–Altman plot: comparison of different anterior segment parameters. (A) Between-instrument agreement (ANTERION vs. CASIAII). (B) Within-instrument agreement (ANTERION). (C) Within-instrument agreement (CASIAII).

Figure 2

Regression analysis of the anterior segment parameters measured from ANTERION and CASIAII. ACD, anterior chamber depth; PD, pupil diameter; SSD, scleral spur-scleral spur distance; LV, lens vault; angle open distance 500 (AOD500); trabecular-iris space area 500 (TISA500).

Figure 3

An eye with open angle (A) and an eye with primary angle closure (B) imaged by the ANTERION and CASIAII. The scleral spur locations were manually marked (middle panel); the anterior and posterior boundaries of the cornea and the lens were automatically segmented by the respective instruments (right panel). ACD, anterior chamber depth; PD, pupil diameter; SSD, scleral spurs distance; LV, lens vault; AOD, angle opening distance at 500 µm; TISA, trabecular iris space area at 500 µm. Only the horizontal scan (0°–180°) are shown.