The dark room provocative test revisited: The role of Ultrasound Biomicroscopy (UBM)

Purpose. To quantify the difference in angle recess area (ARA) under dark and light illumination in eyes with narrow angles. Methods. UBM and A-scan biometry were performed on 11 eyes of 11 previously untreated patients with relative pupillary block (RPB) and 7 eyes of 7 patients with plateau iris configuration (PIC). PIC was defined on the basis of absence of a ciliary sulcus on UBM. A perpendicular was drawn from a point on the corneal endothelium 750 μm anterior to sclerar spur to the iris surface. The angle recess was defined as the triangle demarcated by this line. Area measurements were achieved for each image using a custom-designed program capable of tracing irregular borders. Results. Although PIC patients tended to be younger (p=0.07), refractive error (p=0.48) and axial length (p=0.91) were similar. In dark conditions, the angle narrowed in 10/11 RPB (mean ARA, 0.07 ± 0.04 vs. 0.04 ± 0.03 mm²; p=0.001, paired t-Test) and 6/7 PIC eyes (0.10 ± 0.05 vs. 0.06 ± 0.03 mm²; p=0.06, paired t-Test). 6/11 (55%) and 2/7 (29%) of RPB and PIC eyes with anatomically open angles in lighted conditions developed appositional closure under dark conditions. Conclusion. UBM can detect small differences in angle configuration and angle-closure during dark room provocation. Dark room gonioscopy provides a better assessment of angle occludability than does gonioscopy under lighted conditions.