Abstract
Purpose::
To compare UBM, SL-OCT and gonioscopy for assessment of anatomically narrow angles (ANA).
Methods::
Eyes with ANA (Shaffer grade ≤ 2) were imaged under light and dark conditions using SL-OCT and UBM. Angle opening distance at 500 microns (AOD 500) was recorded using each device for superior and inferior angles. SL-OCT and UBM images and gonioscopy under dark conditions were assessed for iridotrabecular contact (ITC). Sensitivity, specificity and predictive values were evaluated; Kappa statistic was used to measure reproducibility between devices.
Results::
Mean patient age was 59.2 ± 12.6 (SD) years and mean refractive error was +1.4 ± 1.2 D (range -0.50 to +4.50 D). In both superior and inferior angles, AOD 500 was less when measured by UBM compared to SL-OCT. Differences between instruments were highly significant in the inferior angle in light and dark conditions (paired t-test, all p<0.0001). In the superior angle, a highly significant difference was seen in light (p=0.002), but not in the dark (p=0.153). When controlled for light and dark conditions, differences remained highly significant for superior (p=0.006) and inferior angles (p<0.001, two-way analysis of variance). Specifying UBM as the gold standard for ITC, SL-OCT had 80% sensitivity and 87% specificity in the superior angle; sensitivity was 100% with 62% specificity in inferior angle. Gonioscopy had 95% and 85% sensitivity in the superior and inferior angles, respectively, with a specificity of 67% in both locations. Both UBM and SLOCT showed good reproducibility with kappa values ranging from 0.65 to 0.47.
Conclusions::
Multiple factors influence the appearance of the angle, including method of assessment, the software used to process images, illumination, patient posture and contact during the procedure. SL-OCT appears to underestimate the frequency of ITC. Differences in detection of ITC among devices require careful investigation, especially if SL-OCT is to be considered as a screening tool or a gold-standard for the detection of angle-closure.
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • anterior segment • imaging/image analysis: clinical