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To determine clinical factors and ultrasound biomicroscopic (UBM) findings associated with a positive prone dark-room provocative test (DRPT) in patients with narrow angles after laser peripheral iridotomy (LPI).Seventeen eyes with a positive DRPT and 18 eyes with a negative DRPT were included in this comparative case series, based on chart review of patients diagnosed with narrow angles persisting after LPI who had undergone clinical evaluation with a 45-minute DRPT and UBM imaging. Subjects with a positive DRPT [an increase of intraocular pressure (IOP) of 6 mm Hg or more] were compared with a negative DRPT control group. Charts were reviewed for age, refraction and gonioscopic examination. UBM measurements obtained included the anterior chamber depth, angle opening distance at 500 μm, angle recess area, anterior chamber angle, trabecular-ciliary process distance, iris thickness, iris-ciliary process distance, height of plateau, and distance of iris-cornea contact.Mean increase in IOP was 11.1±3.5 mm Hg in the positive DRPT group (group A) and 0.9±0.1 mm Hg in the negative DRPT (group B). On indentation gonioscopy, patients in group A had significantly more synechial angle closure of 180 degrees or more (35% vs. 0%, P=0.008), more frequent double-hump sign (59% vs. 11%, P=0.005), and significantly more patients in this group had at least one of these findings, (13/16 vs. 2/15, P=<0.001). Mean age did not differ between groups (P=0.88). There were significantly more women in group B (58% men in group A and 83% women in group B, P=0.01). Mean refraction was +3.41±2.27 D in group A and +2.60±2.06 D in group B (P=0.32). There were no statistically significant differences in any of the UBM parameters between the 2 groups.A positive DRPT was found in patients presenting a more compromised drainage angle after LPI, due to anterior synechiae and/or an anteriorly positioned ciliary body as shown by the presence of a double-hump sign. DRPT may help identify patients at higher risk of intermittent increases in IOP among those presenting persistent narrow angles after LPI, and indentation gonioscopy remains an important step in evaluating these patients.